One document matched: draft-bierman-netconf-rfc6536bis-00.xml
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<rfc category="std"
obsoletes="6536"
docName="draft-bierman-netconf-rfc6536bis-00"
ipr="trust200902">
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<front>
<title abbrev="NACM">
Network Configuration Protocol (NETCONF) Access Control Model
</title>
<author fullname="Andy Bierman"
initials="A.B."
surname="Bierman">
<organization>YumaWorks</organization>
<address>
<postal>
<street>685 Cochran St.</street>
<street>Suite #160</street>
<city>Simi Valley</city>
<region>CA</region>
<code>93065</code>
<country>USA</country>
</postal>
<email>andy@yumaworks.com</email>
</address>
</author>
<author fullname="Martin Bjorklund"
initials="M.B."
surname="Bjorklund">
<organization>Tail-f Systems</organization>
<address>
<email>mbj@tail-f.com</email>
</address>
</author>
<date month="October" day="26" year="2016" />
<area>Management</area>
<workgroup>Internet Engineering Task Force</workgroup>
<keyword>NETCONF</keyword>
<keyword>RESTCONF</keyword>
<keyword>YANG</keyword>
<keyword>XML</keyword>
<abstract>
<t>
The standardization of network configuration interfaces for use
with the Network Configuration Protocol (NETCONF) or RESTCONF
protocol requires a structured and secure
operating environment that promotes human usability and
multi-vendor interoperability. There is a need for standard
mechanisms to restrict NETCONF or RESTCONF protocol access for particular
users to a pre-configured subset of all available NETCONF or
RESTCONF protocol operations and content.
This document defines such an access control model.
</t>
<t>
This document obsoletes RFC 6536.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
The NETCONF and RESTCONF protocols do not provide any standard
mechanisms to restrict the protocol operations and content that
each user is authorized to access.
</t>
<t>
There is a need for interoperable management of the
controlled access to administrator-selected portions of the
available NETCONF or RESTCONF content within a particular server.
</t>
<t>
This document addresses access control mechanisms for the
Operations and Content layers of NETCONF, as defined in <xref
target="RFC6241"/>, and RESTCONF, as defined
in <xref target="I-D.ietf-netconf-restconf" />.
It contains three main sections:
<list style="numbers">
<t>Access Control Design Objectives</t>
<t>NETCONF Access Control Model (NACM)</t>
<t>YANG Data Model (ietf-netconf-acm.yang)</t>
</list>
</t>
<t>
YANG version 1.1 <xref target="RFC7950"/>
adds two new constructs that need special access control
handling. The "action" statement is similar to the "rpc"
statement, except it is located within a data node.
The "notification" statement can also be located within
a data node.
</t>
<section title="Terminology">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" in this document are to be interpreted as
described in <xref target="RFC2119"/>.
</t>
<t>
The following terms are defined in
<xref target="RFC6241"/> and
are not redefined here:
<list style="symbols">
<t>client</t>
<t>datastore</t>
<t>protocol operation</t>
<t>server</t>
<t>session</t>
<t>user</t>
</list>
</t>
<t>
The following terms are defined in
<xref target="RFC7950"/>.
and are not redefined here:
<list style="symbols">
<t>action</t>
<t>data node</t>
<t>data definition statement</t>
</list>
</t>
<t>
The following terms are defined in
<xref target="I-D.ietf-netconf-restconf"/>.
and are not redefined here:
<list style="symbols">
<t>data resource</t>
<t>datastore resource</t>
<t>operation resource</t>
</list>
</t>
<t>
The following terms are used throughout this document:
<list style="hanging">
<t hangText="access control:">
A security feature provided by the NETCONF server
that allows an administrator to restrict access to a
subset of all NETCONF protocol operations and data,
based on various criteria.
</t>
<t hangText="access control model (ACM):">
A conceptual model used to configure and monitor
the access control procedures desired by the administrator
to enforce a particular access control policy.
</t>
<t hangText="access control rule:">
The criterion used to determine if a
particular NETCONF protocol operation will be
permitted or denied.
</t>
<t hangText="access operation:">
How a request attempts to access a conceptual object.
One of "none", "read", "create", "delete", "update", or
"execute".
</t>
<t hangText="data node hierarchy:">
The hierarchy of data nodes that identifies
the specific "action" or "notification" node
in the datastore.
</t>
<t hangText="recovery session:">
A special administrative session that is given
unlimited NETCONF access and is exempt from all access
control enforcement. The mechanism(s) used
by a server to control and identify whether or not
a session is a recovery session are
implementation specific and outside
the scope of this document.
</t>
<t hangText="write access:">
A shorthand for the "create", "delete", and "update"
access operations.
</t>
</list>
</t>
</section>
<section title="Changes Since RFC 6535">
<t>
The NACM procedures and data model have been updated
to support new data modeling capabilities in the
version 1.1. of the YANG data modeling language.
The "action" and "notification" statements can be used within
data nodes to define data-model specific operations and
notifications.
</t>
<t>
An important use-case for these new YANG
statements is the increased access control granularity
that can be achieved over top-level "rpc" and "notification"
statements. The new "action" and "notification" statements
are used within data nodes, and access to the action or
notification can be restricted to specific instances
of these data nodes.
</t>
<t>
Support for the RESTCONF protocol has been added.
The RESTCONF operations are similar to the NETCONF operations,
so a simple mapping to the existing NACM procedures
and data model is possible.
</t>
</section>
</section>
<section title="Access Control Design Objectives">
<t>
This section documents the design objectives for the NETCONF
Access Control Model presented in <xref target="acm"/>.
</t>
<section title="Access Control Points">
<t>
NETCONF allows new protocol operations to be
added at any time, and the YANG Data Modeling Language
supports this feature. It is not possible to
design an ACM for NETCONF that
only focuses on a static set of protocol operations,
like some other protocols. Since few assumptions
can be made about an arbitrary protocol operation,
the NETCONF architectural server components need to
be protected at three conceptual control points.
</t>
<t>
These access control points, described in <xref
target="control_points"/>, are as follows:
<list style="hanging">
<t hangText="protocol operation:">
Permission to invoke specific protocol operations.
</t>
<t hangText="datastore:">
Permission to read and/or alter
specific data nodes within any datastore.
</t>
<t hangText="notification:">
Permission to receive
specific notification event types.
</t>
</list>
</t>
<t>
<figure anchor="control_points">
<artwork><![CDATA[ +-------------+ +-------------+
client | protocol | | data node |
request --> | operation | -------------> | access |
| allowed? | datastore | allowed? |
+-------------+ or state +-------------+
data access
+----------------+
| notification |
event --> | allowed? |
+----------------+]]>
</artwork>
</figure>
</t>
</section>
<section title="Simplicity">
<t>
There is concern that a complicated ACM will not
be widely deployed because it is too hard to use.
It needs to be easy to do simple things and possible to do
complex things, instead of hard to do everything.
</t>
<t>
Configuration of the access control system needs to be as
simple as possible. Simple and common tasks need to be easy
to configure and require little expertise or domain-specific
knowledge. Complex tasks are possible using additional
mechanisms, which may require additional expertise.
</t>
<t>
A single set of access control rules ought to be able
to control all types of NETCONF protocol operation invocation,
all datastore access, and all notification events.
</t>
<t>
Access control ought to be defined with a small and familiar
set of permissions, while still allowing full control
of NETCONF datastore access.
</t>
</section>
<section title="Procedural Interface">
<t>
The NETCONF protocol uses a remote procedure call model
and an extensible set of protocol operations.
Access control for any possible protocol operation is necessary.
</t>
</section>
<section title="Datastore Access">
<t>
It is necessary to control access to specific nodes and
subtrees within the NETCONF datastore, regardless of which
protocol operation, standard or proprietary, was used to
access the datastore.
</t>
</section>
<section title="Users and Groups">
<t>
It is necessary that access control rules for a single user or
a configurable group of users can be configured.
</t>
<t>
The ACM needs to support the concept of administrative groups,
to support the well-established distinction between
a root account and other types of less-privileged
conceptual user accounts.
These groups need to be configurable by the administrator.
</t>
<t>
It is necessary that the user-to-group mapping can be
delegated to a central server, such as a RADIUS server <xref
target="RFC2865"/><xref target="RFC5607"/>. Since
authentication is performed by the NETCONF transport layer
and RADIUS performs authentication and service authorization
at the same time, the underlying NETCONF transport needs to be
able to report a set of group names associated with the user
to the server. It is necessary that the administrator can
disable the usage of these group names within the ACM.
</t>
</section>
<section title="Maintenance">
<t>
It ought to be possible to disable part or all of the
access control model enforcement procedures without deleting any
access control rules.
</t>
</section>
<section title="Configuration Capabilities">
<t>
Suitable configuration and monitoring mechanisms
are needed to allow an administrator to easily manage all
aspects of the ACM's behavior. A standard data model,
suitable for use with the <edit-config>
protocol operation,
needs to be available for this purpose.
</t>
<t>
Access control rules to restrict access operations on specific
subtrees within the configuration datastore need to
be supported.
</t>
</section>
<section title="Identifying Security-Sensitive Content">
<t>
One of the most important aspects of the data model
documentation, and biggest concerns during deployment,
is the identification of security-sensitive content.
This applies to protocol operations in NETCONF, not just data
and notifications.
</t>
<t>
It is mandatory for security-sensitive objects
to be documented in the Security Considerations
section of an RFC. This is nice, but it
is not good enough, for the following reasons:
<list style="symbols">
<t>
This documentation-only approach forces administrators to
study the RFC and determine if there are any
potential security risks introduced by a new
data model.
</t>
<t>
If any security risks are identified, then
the administrator must study some more RFC text
and determine how to mitigate the security risk(s).
</t>
<t>
The ACM on each server must be configured to
mitigate the security risks, e.g., require
privileged access to read or write the
specific data identified in the Security
Considerations section.
</t>
<t>
If the ACM is not pre-configured, then there
will be a time window of vulnerability
after the new data model is loaded and before
the new access control rules for that data model
are configured, enabled, and debugged.
</t>
</list>
</t>
<t>
Often, the administrator just wants to disable
default access to the secure content, so
no inadvertent or malicious changes can be made
to the server. This allows the default rules
to be more lenient, without significantly
increasing the security risk.
</t>
<t>
A data model designer needs to be able to
use machine-readable statements to identify
NETCONF content, which needs to be protected by default.
This will allow client and server tools to automatically
identify data-model-specific security risks, by
denying access to sensitive data unless the user is
explicitly authorized to perform the requested access operation.
</t>
</section>
</section>
<section title="NETCONF Access Control Model (NACM)"
anchor="acm">
<section title="Introduction">
<t>
This section provides a high-level overview of the
access control model structure. It describes the
NETCONF protocol message processing model and the conceptual
access control requirements within that model.
</t>
<section title="Features">
<t>
The NACM data model provides the following features:
<list style="symbols">
<t>
Independent control of remote procedure call (RPC),
action, data, and notification access.
</t>
<t>
Simple access control rules configuration
data model that is easy to use.
</t>
<t>
The concept of an emergency recovery session
is supported, but configuration of the server
for this purpose is beyond the scope of this document.
An emergency recovery session will bypass all access
control enforcement, in order to allow it to
initialize or repair the NACM configuration.
</t>
<t>
A simple and familiar set of datastore permissions is
used.
</t>
<t>
Support for YANG security tagging (e.g.,
"nacm:default-deny-write" statement) allows default
security modes to automatically exclude sensitive data.
</t>
<t>
Separate default access modes for read, write, and
execute permissions.
</t>
<t>
Access control rules are applied to configurable groups
of users.
</t>
<t>
The access control enforcement procedures can be disabled during
operation, without deleting any access control rules,
in order to debug operational problems.
</t>
<t>
Access control rules are simple to configure.
</t>
<t>
The number of denied protocol operation requests
and denied datastore write requests can be
monitored by the client.
</t>
<t>
Simple unconstrained YANG instance identifiers
are used to configure access control rules for
specific data nodes.
</t>
</list>
</t>
</section>
<section title="External Dependencies">
<t>
The <xref target="RFC6241">NETCONF protocol</xref>
is used for network management purposes within this document.
</t>
<t>
The <xref target="I-D.ietf-netconf-restconf">RESTCONF protocol</xref>
is used for network management purposes within this document.
</t>
<t>
The <xref target="RFC7950">
YANG Data Modeling Language</xref>
is used to define the data models for use
with the NETCONF or RESTCONF protocols.
YANG is also used to define the data model in
this document.
</t>
</section>
<section title="Message Processing Model" anchor="message-proc-model" >
<t>
The following diagram shows the conceptual message
flow model, including the points at which access
control is applied during NETCONF message processing.
</t>
<t>
RESTCONF operations are mapped to the access control model
based on the HTTP method and resource class used in the operation.
For example, a POST method on a data resource is considered
"write data node" access, but a POST method on an operation
resource is considered "operation" access.
</t>
<t>
<figure anchor="NACM_model">
<artwork>
<![CDATA[
+-------------------------+
| session |
| (username) |
+-------------------------+
| ^
V |
+--------------+ +---------------+
| message | | message |
| dispatcher | | generator |
+--------------+ +---------------+
| | ^ ^
| V | |
| +=============+ | |
| | pre-read | | |
| | data node | | |
| | acc. ctl | | |
| +=============+ | |
| | | |
V V | |
+===========+ +-------------+ +----------------+
| operation |---> | reply | | <notification> |
| acc. ctl | | generator | | generator |
+===========+ +-------------+ +----------------+
| ^ ^ ^
V +------+ | |
+-----------+ | +=============+ +================+
| operation | | | read | | <notification> |
| processor |-+ | data node | | access ctl |
| | | acc. ctl | | |
+-----------+ +=============+ +================+
| | ^ ^ ^
V +----------------+ | | |
+===========+ | | | +============+
| write | | | | | pre-read |
| data node | | | | | data node |
| acc. ctl | -----------+ | | | | acc. ctl |
+===========+ | | | | +============+
| | | | | ^
V V V | | |
+---------------+ +-------------------+
| configuration | ---> | server |
| datastore | | instrumentation |
| | <--- | |
+---------------+ +-------------------+]]>
</artwork>
</figure>
</t>
<t>
The following high-level sequence of conceptual processing steps
is executed for each received <rpc> message,
if access control enforcement is enabled:
<list style="symbols">
<t>
For each active session, access control is applied individually to all
<rpc> messages (except <close-session>)
received by the server, unless
the session is identified as a recovery session.
</t>
<t>
If the <action> operation defined in <xref
target="RFC7950"/> is invoked, then read access is
required for all instances in the hierarchy of data nodes
that identifies the specific action in the datastore, and
execute access is required for the action node. If the
user is not authorized to read all the specified data
nodes and execute the action, then the request is
rejected with an "access-denied" error.
</t>
<t>
Otherwise, if the user is not authorized to execute the
specified protocol operation, then the request is
rejected with an "access-denied" error.
</t>
<t>
If the configuration datastore or conceptual state data
is accessed by the protocol operation, then the server
checks if the client is authorized to access the nodes in
the datastore. If the user is not authorized to perform
the requested access operation on the requested data,
then the request is rejected with an "access-denied"
error.
</t>
</list>
</t>
<t>
The following sequence of conceptual processing steps
is executed for each generated notification event,
if access control enforcement is enabled:
<list style="symbols">
<t>
Server instrumentation generates a notification
for a particular subscription.
</t>
<t>
If the notification statement is specified within a data
subtree, as specified in <xref target="RFC7950"/>, then
read access is required for all instances in the
hierarchy of data nodes that identifies the specific
notification in the datastore, and read access is
required for the notification node. If the user is not
authorized to read all the specified data nodes and the
notification node, then the notification is dropped for
that subscription.
</t>
<t>
If the notification statement is a top-level statement,
the notification access control enforcer checks the
notification event type, and if it is one that the user
is not authorized to read, then the notification is
dropped for that subscription.
</t>
</list>
</t>
</section>
</section>
<section title="Datastore Access">
<t>
The same access control rules apply to all
datastores, for example, the candidate configuration
datastore or the running configuration datastore.
</t>
<t>
Only the standard NETCONF datastores (candidate, running,
and startup) are controlled by NACM. Local or remote
files or datastores accessed via the <url>
parameter are not controlled by NACM.
A standalone RESTCONF server (i.e., not co-located with a
NETCONF server) applies NACM rules to a conceptual datastore,
since datastores are not supported in RESTCONF.
</t>
<section title="Access Rights">
<t>
A small set of hard-wired datastore access rights is needed
to control access to all possible NETCONF protocol operations,
including vendor extensions to the standard protocol operation set.
</t>
<t>
The "CRUDX" model can support all NETCONF
protocol operations:
<list style="symbols">
<t>
Create: allows the client to add a new data node
instance to a datastore.
</t>
<t>
Read: allows the client to read a data node instance
from a datastore or receive the notification event type.
</t>
<t>
Update: allows the client to update an existing data
node instance in a datastore.
</t>
<t>
Delete: allows the client to delete a data node
instance from a datastore.
</t>
<t>
eXec: allows the client to execute the operation.
</t>
</list>
</t>
</section>
<section title="RESTCONF Methods">
<t>
The RESTCONF protocol utilizes HTTP methods to perform
datastore operations, similar to the NETCONF protocol.
The NACM procedures were originally written for
NETCONF protocol operations so the RESTCONF methods
are mapped to NETCONF operations for the purpose of
access control processing. The enforcement procedures
described within this document apply to both protocols
unless explicitly stated otherwise.
</t>
<t>
Not all RESTCONF methods are subject to access control.
The following table specifies how each method is
mapped to NETCONF protocol operations. The value 'none'
indicates that NACM is not applied at all to the specific
RESTCONF method.
</t>
<texttable anchor="restconf_method_table"
title="Mapping RESTCONF Methods to NETCONF">
<ttcol align='left'>method</ttcol>
<ttcol align='left'>resource class</ttcol>
<ttcol align='left'>NETCONF operation</ttcol>
<ttcol align='left'>Edit operation</ttcol>
<c>OPTIONS</c>
<c>all</c>
<c>none</c>
<c>N/A</c>
<c>HEAD</c>
<c>all</c>
<c><get></c>
<c>N/A</c>
<c>GET</c>
<c>all</c>
<c><get></c>
<c>N/A</c>
<c>POST</c>
<c>datastore, data</c>
<c><edit-config></c>
<c>create</c>
<c>POST</c>
<c>operation</c>
<c>specified operation</c>
<c>N/A</c>
<c>PUT</c>
<c>data</c>
<c><edit-config></c>
<c>create, replace</c>
<c>PUT</c>
<c>datastore</c>
<c><copy-config></c>
<c>replace</c>
<c>PATCH</c>
<c>data, datastore</c>
<c><edit-config></c>
<c>merge</c>
<c>DELETE</c>
<c>data</c>
<c><edit-config></c>
<c>delete</c>
</texttable>
</section>
<section title="<get> and <get-config> Operations">
<t>
Data nodes to which the client does not have read access are
silently omitted from the <rpc-reply> message. This
is done to allow NETCONF filters for <get> and
<get-config> to function properly, instead of causing
an "access-denied" error because the filter criteria would
otherwise include unauthorized read access to some data
nodes. For NETCONF filtering purposes, the selection
criteria is applied to the subset of nodes that the user is
authorized to read, not the entire datastore.
</t>
</section>
<section title="<edit-config> Operation">
<t>
The NACM access rights are not directly coupled to the
<edit-config> "operation" attribute, although they are
similar. Instead, a NACM access right applies to all
protocol operations that would result in a particular access
operation to the target datastore.
This section describes
how these access rights apply to the specific access
operations supported by the <edit-config> protocol operation.
</t>
<t>
If the effective access operation is "none"
(i.e., default-operation="none")
for a particular data node,
then no access control is applied to that data node.
This is required to allow access to a subtree within
a larger data structure. For example, a user may be
authorized to create a new "/interfaces/interface" list entry
but not be authorized to create or delete its
parent container ("/interfaces").
If the "/interfaces" container already exists in
the target datastore, then the effective operation
will be "none" for the "/interfaces" node if an
"/interfaces/interface" list entry is edited.
</t>
<t>
If the protocol operation would result in the
creation of a datastore node and the user does not
have "create" access permission for that node, the
protocol operation is rejected with an
"access-denied" error.
</t>
<t>
If the protocol operation would result in the
deletion of a datastore node and the user does not
have "delete" access permission for that node, the
protocol operation is rejected with an
"access-denied" error.
</t>
<t>
If the protocol operation would result in the
modification of a datastore node and the user does
not have "update" access permission for that node,
the protocol operation is rejected with an
"access-denied" error.
</t>
<t>
A "merge" or "replace" <edit-config> operation may
include data nodes that do not alter portions of the
existing datastore. For example, a container or list node
may be present for naming purposes but does not actually
alter the corresponding datastore node. These unaltered
data nodes are ignored by the server and do not require any
access rights by the client.
</t>
<t>
A "merge" <edit-config> operation may include data
nodes but not include particular child data nodes that are
present in the datastore. These missing data nodes within
the scope of a "merge" <edit-config> operation are
ignored by the server and do not require any access rights
by the client.
</t>
<t>
The contents of specific restricted datastore nodes MUST NOT
be exposed in any <rpc-error> elements
within the reply.
</t>
</section>
<section title="<copy-config> Operation">
<t>
Access control for the <copy-config> protocol operation
requires special consideration because the administrator may be
replacing the entire target datastore.
</t>
<t>
If the source of the <copy-config> protocol
operation is the running configuration datastore
and the target is the startup configuration
datastore, the client is only required to
have permission to execute the <copy-config>
protocol operation.
</t>
<t>
Otherwise:
<list style="symbols">
<t>
If the source of the <copy-config> operation is a
datastore, then data nodes to which the client does not
have read access are silently omitted.
</t>
<t>
If the target of the <copy-config> operation is a
datastore, the client needs access to the modified
nodes, specifically:
<list style="symbols">
<t>
If the protocol operation would result in the
creation of a datastore node and the user does not
have "create" access permission for that node, the
protocol operation is rejected with an
"access-denied" error.
</t>
<t>
If the protocol operation would result in the
deletion of a datastore node and the user does not
have "delete" access permission for that node, the
protocol operation is rejected with an
"access-denied" error.
</t>
<t>
If the protocol operation would result in the
modification of a datastore node and the user does
not have "update" access permission for that node,
the protocol operation is rejected with an
"access-denied" error.
</t>
</list>
</t>
</list>
</t>
</section>
<section title="<delete-config> Operation">
<t>
Access to the <delete-config> protocol operation
is denied by default. The "exec-default" leaf
does not apply to this protocol operation.
Access
control rules must be explicitly configured to
allow invocation by a non-recovery session.
</t>
</section>
<section title="<commit> Operation">
<t>
The server MUST determine the exact nodes in the running
configuration datastore that are actually different and
only check "create", "update", and "delete" access
permissions for this set of nodes, which could be empty.
</t>
<t>
For example, if a session can read the entire datastore
but only change one leaf, that session needs to be
able to edit and commit that one leaf.
</t>
</section>
<section title="<discard-changes> Operation">
<t>
The client is only required to
have permission to execute the <discard-changes>
protocol operation. No datastore permissions are needed.
</t>
</section>
<section title="<kill-session> Operation">
<t>
The <kill-session> operation does not directly
alter a datastore. However, it allows one session
to disrupt another session that is editing a datastore.
</t>
<t>
Access to the <kill-session> protocol operation
is denied by default. The "exec-default" leaf
does not apply to this protocol operation. Access
control rules must be explicitly configured to
allow invocation by a non-recovery session.
</t>
</section>
</section>
<section title="Model Components">
<t>
This section defines the conceptual components
related to the access control model.
</t>
<section title="Users">
<t>
A "user" is the conceptual entity that is associated
with the access permissions granted to a particular session.
A user is identified by a string that is unique
within the server.
</t>
<t>
As described in <xref target="RFC6241"/>,
the username string is derived from the transport layer
during session establishment. If the transport layer cannot
authenticate the user, the session is terminated.
</t>
</section>
<section title="Groups">
<t>
Access to a specific NETCONF protocol operation is granted to
a session, associated with a group, not a user.
</t>
<t>
A group is identified by its name. All group names are
unique within the server.
</t>
<t>
A group member is identified by a username string.
</t>
<t>
The same user can be a member of multiple groups.
</t>
</section>
<section title="Emergency Recovery Session">
<t>
The server MAY support a recovery session mechanism,
which will bypass all access control enforcement.
This is useful for restricting initial access
and repairing a broken access control configuration.
</t>
</section>
<section title="Global Enforcement Controls">
<t>
There are five global controls that are used to
help control how access control is enforced.
</t>
<section title="enable-nacm Switch">
<t>
A global "enable-nacm" on/off switch is provided to enable
or disable all access control enforcement.
When this global switch is set to "true", then all
requests are checked against the access control rules
and only permitted if configured to allow the
specific access request.
When this global switch is set to "false", then all access
requested are permitted.
</t>
</section>
<section title="read-default Switch">
<t>
An on/off "read-default" switch is provided to
enable or disable default access
to receive data in replies and notifications.
When the "enable-nacm" global switch is set to "true", then this
global switch is relevant if no matching
access control rule is found to explicitly
permit or deny read access to the requested
NETCONF datastore data or notification event type.
</t>
<t>
When this global switch is set to "permit" and no matching
access control rule is found for the NETCONF
datastore read or notification event requested, then access
is permitted.
</t>
<t>
When this global switch is set to "deny" and no matching
access control rule is found for the NETCONF
datastore read or notification event requested, then access
is denied.
</t>
</section>
<section title="write-default Switch">
<t>
An on/off "write-default" switch is provided to
enable or disable default access
to alter configuration data.
When the "enable-nacm" global switch is set to "true", then this
global switch is relevant if no matching
access control rule is found to explicitly
permit or deny write access to the requested
NETCONF datastore data.
</t>
<t>
When this global switch is set to "permit" and no matching
access control rule is found for the NETCONF
datastore write requested, then access is permitted.
</t>
<t>
When this global switch is set to "deny" and no matching
access control rule is found for the NETCONF
datastore write requested, then access
is denied.
</t>
</section>
<section title="exec-default Switch">
<t>
An on/off "exec-default" switch is provided to
enable or disable default access
to execute protocol operations.
When the "enable-nacm" global switch is set to "true",
then this global switch is relevant if no matching
access control rule is found to explicitly
permit or deny access to the requested
NETCONF protocol operation.
</t>
<t>
When this global switch is set to "permit" and no matching
access control rule is found for the NETCONF
protocol operation requested, then access is permitted.
</t>
<t>
When this global switch is set to "deny" and no matching
access control rule is found for the NETCONF
protocol operation requested, then access is denied.
</t>
</section>
<section title="enable-external-groups Switch">
<t>
When this global switch is set to "true", the group names
reported by the NETCONF transport layer for a session are
used together with the locally configured group names to
determine the access control rules for the session.
</t>
<t>
When this switch is set to "false", the group names
reported by the NETCONF transport layer are ignored by
NACM.
</t>
</section>
</section>
<section title="Access Control Rules">
<t>
There are four types of rules available in NACM:
<list style="hanging">
<t hangText="module rule:">
controls access for definitions in
a specific YANG module, identified by its
name.
</t>
<t hangText="protocol operation rule:">
controls access for a
specific protocol operation, identified by its
YANG module and name.
</t>
<t hangText="data node rule:">
controls access for a
specific data node, identified by its
path location within the conceptual
XML document for the data node.
</t>
<t hangText="notification rule:">
controls access for a
specific notification event type, identified by its
YANG module and name.
</t>
</list>
</t>
</section>
</section>
<section title="Access Control Enforcement Procedures">
<t>
There are seven separate phases that need to be addressed,
four of which are related to the NETCONF message processing model (<xref
target="message-proc-model" />).
In addition, the initial startup mode for a NETCONF server,
session establishment, and "access-denied" error-handling
procedures also need to be considered.
</t>
<t>
The server MUST use the access control rules in effect
at the time it starts processing the message.
The same access control rules MUST stay in effect for
the processing of the entire message.
</t>
<section title="Initial Operation">
<t>
Upon the very first startup of the NETCONF server,
the access control configuration will probably
not be present. If it isn't,
a server MUST NOT allow any write access to
any session role except a recovery session.
</t>
<t>
Access rules are enforced any time a
request is initiated from a user session.
Access control is not enforced for
server-initiated access requests, such as the
initial load of the running datastore, during bootup.
</t>
</section>
<section title="Session Establishment">
<t>
The access control model applies specifically
to the well-formed XML content transferred between a client
and a server after session establishment has been completed
and after the <hello> exchange has been successfully
completed.
</t>
<t>
Once session establishment is completed and a user
has been authenticated, the NETCONF transport layer reports
the username and a possibly empty set of group names
associated with the user to the NETCONF server. The NETCONF
server will enforce the access control rules, based on the
supplied username, group names, and the configuration
data stored on the server.
</t>
</section>
<section title='"access-denied" Error Handling'>
<t>
The "access-denied" error-tag is generated when
the access control system denies access to either a
request to invoke a protocol operation or a request to
perform a particular access operation on the configuration
datastore.
</t>
<t>
A server MUST NOT include any information the client is not
allowed to read in any <error-info> elements within the
<rpc-error> response.
</t>
</section>
<section title="Incoming RPC Message Validation">
<t>
The diagram below shows the basic
conceptual structure of the access control processing model
for incoming NETCONF <rpc> messages within a server.
</t>
<t>
<figure anchor="NACM_incoming">
<artwork>
<![CDATA[ NETCONF server
+------------+
| XML |
| message |
| dispatcher |
+------------+
|
|
V
+------------+
| NC-base NS |
| <rpc> |
+------------+
| | |
| | +-------------------------+
| +------------+ |
V V V
+-----------+ +---------------+ +------------+
| Vendor NS | | NC-base NS | | NC-base NS |
| <my-edit> | | <edit-config> | | <unlock> |
+-----------+ +---------------+ +------------+
| |
| |
V V
+----------------------+
| |
| configuration |
| datastore |
+----------------------+]]>
</artwork>
</figure>
</t>
<t>
Access control begins with the message dispatcher.
</t>
<t>
After the server validates the <rpc> element
and determines the namespace URI and the element
name of the protocol operation being requested, the server
verifies that the user is authorized
to invoke the protocol operation.
</t>
<t>
The server MUST separately authorize every protocol operation
by following these steps:
<list style="numbers">
<t>
If the "enable-nacm" leaf is set to "false", then the
protocol operation is permitted.
</t>
<t>
If the requesting session is identified as a recovery session,
then the protocol operation is permitted.
</t>
<t>
If the requested operation is the NETCONF
<close-session> protocol operation, then
the protocol operation is permitted.
</t>
<t>
Check all the "group" entries for ones that contain a
"user-name" entry that equals the username for the
session making the request. If the
"enable-external-groups" leaf is "true", add to these
groups the set of groups provided by the transport layer.
</t>
<t>
If no groups are found, continue with step 10.
</t>
<t>
Process all rule-list entries, in the order they
appear in the configuration.
If a rule-list's "group" leaf-list does not match any
of the user's groups, proceed to the next rule-list entry.
</t>
<t>
For each rule-list entry found, process all rules, in
order, until a rule that matches the requested access operation
is found. A rule matches if all of the following
criteria are met:
<list style="symbols">
<t>
The rule's "module-name" leaf is "*" or equals the
name of the YANG module where the protocol operation
is defined.
</t>
<t>
The rule does not have a "rule-type" defined or the
"rule-type" is "protocol-operation" and the
"rpc-name" is "*" or equals the name of the requested protocol
operation.
</t>
<t>
The rule's "access-operations" leaf has the "exec" bit
set or has the special value "*".
</t>
</list>
</t>
<t>
If a matching rule is found, then the "action" leaf
is checked. If it is equal to "permit", then the protocol
operation is permitted; otherwise, it is denied.
</t>
<t>
At this point, no matching rule was found in any rule-list
entry.
</t>
<t anchor="rpc-default">
If the requested protocol operation is defined in a
YANG module advertised in the server capabilities and
the "rpc" statement contains a "nacm:default-deny-all"
statement, then the protocol operation is denied.
</t>
<t>
If the requested protocol operation is the NETCONF
<kill-session> or <delete-config>, then the
protocol operation is denied.
</t>
<t>
If the "exec-default" leaf is set to "permit", then
permit the protocol operation; otherwise, deny the
request.
</t>
</list>
</t>
<t>
If the user is not authorized to invoke the protocol operation,
then an <rpc-error> is generated with the following
information:
<list style="hanging">
<t hangText="error-tag:">access-denied</t>
<t hangText="error-path:">
Identifies the requested protocol operation. The following
example represents the <edit-config> protocol
operation in the
NETCONF base namespace:
<figure>
<artwork>
<![CDATA[<error-path
xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0">
/nc:rpc/nc:edit-config
</error-path>
]]></artwork>
</figure>
</t>
</list>
</t>
<t>
If a datastore is accessed, either directly or as a side
effect of the protocol operation, then the server MUST
intercept the access operation and make sure the user is
authorized to perform the requested access operation on the
specified data, as defined in <xref target="node-access"/>.
</t>
</section>
<section title="Data Node Access Validation" anchor="node-access">
<t>
If a data node within a datastore is accessed, or an action
or notification tied to a data node, then the
server MUST ensure that the user is authorized to
perform the requested "read", "create", "update", "delete",
or "execute"
access operation on the specified data node.
</t>
<t>
If an action is requested to be executed, the server MUST
ensure that the user is authorized to perform the "execute"
access operation on the requested action.
</t>
<t>
If a notification tied to a data node is generated, the server MUST
ensure that the user is authorized to perform the "read"
access operation on the requested notification.
</t>
<t>
The data node access request is authorized by following
these steps:
<list style="numbers">
<t>
If the "enable-nacm" leaf is set to "false", then the
access operation is permitted.
</t>
<t>
If the requesting session is identified as a
recovery session, then the access operation is permitted.
</t>
<t>
Check all the "group" entries for ones that contain a
"user-name" entry that equals the username for the
session making the request. If the
"enable-external-groups" leaf is "true", add to these
groups the set of groups provided by the transport layer.
</t>
<t>
If no groups are found, continue with step 9.
</t>
<t>
Process all rule-list entries, in the order
they appear in the configuration. If a
rule-list's "group" leaf-list does not match any
of the user's groups, proceed to the next rule-list entry.
</t>
<t>
For each rule-list entry found, process all rules, in
order, until a rule that matches the requested
access operation is found. A rule matches if all of the following
criteria are met:
<list style="symbols">
<t>
The rule's "module-name" leaf is "*" or equals the
name of the YANG module where the requested data node
is defined.
</t>
<t>
The rule does not have a "rule-type" defined or the
"rule-type" is "data-node" and the "path" matches the
requested data node, action node, or notification node.
</t>
<t>
For a "read" access operation, the rule's
"access-operations" leaf has the "read" bit set or
has the special value "*".
</t>
<t>
For a "create" access operation, the rule's
"access-operations" leaf has the "create" bit set or
has the special value "*".
</t>
<t>
For a "delete" access operation, the rule's
"access-operations" leaf has the "delete" bit set or
has the special value "*".
</t>
<t>
For an "update" access operation, the rule's
"access-operations" leaf has the "update" bit set or
has the special value "*".
</t>
<t>
For an "execute" access operation, the rule's
"access-operations" leaf has the "exec" bit set or
has the special value "*".
</t>
</list>
</t>
<t>
If a matching rule is found, then the "action" leaf
is checked. If it is equal to "permit", then the
data node access is permitted; otherwise, it is denied.
For a "read" access operation, "denied" means that the requested
data is not returned in the reply.
</t>
<t>
At this point, no matching rule was found in any rule-list
entry.
</t>
<t anchor="data-node-default">
For a "read" access operation, if the requested data node is defined
in a YANG module advertised in the server capabilities
and the data definition statement contains a
"nacm:default-deny-all" statement, then the requested data
node is not included in the reply.
</t>
<t>
For a "write" access operation, if the requested data node
is defined in a YANG module advertised in the server
capabilities and the data definition statement contains
a "nacm:default-deny-write" or a "nacm:default-deny-all"
statement, then the data node access request is denied.
</t>
<t>
For a "read" access operation, if the "read-default" leaf is set to
"permit", then include the requested data node in the reply;
otherwise, do not include the requested data node in the reply.
</t>
<t>
For a "write" access operation, if the "write-default" leaf is set
to "permit", then permit the data node access request;
otherwise, deny the request.
</t>
<t>
For an "execute" access operation, if the "exec-default"
leaf is set to "permit", then permit the request;
otherwise, deny the request.
</t>
</list>
</t>
</section>
<section title="Outgoing <notification> Authorization">
<t>
Configuration of access control rules specifically
for descendant nodes of the notification event type
element are outside the scope of this document.
If the user is authorized to receive the
notification event type, then it is also
authorized to receive any data it contains.
</t>
<t>
If the notification is specified within a data subtree, as
specified in <xref target="RFC7950"/>, then read access to
the notification is required. Processing continues as
described in <xref target="node-access"/>.
</t>
<t>
The following figure shows the conceptual message processing
model for outgoing <notification> messages.
</t>
<t>
<figure anchor="NACM_outgoing_notification">
<artwork>
<![CDATA[
NETCONF server
+------------+
| XML |
| message |
| generator |
+------------+
^
|
+----------------+
| <notification> |
| generator |
+----------------+
^
|
+=================+
| <notification> |
| access control |
| <eventType> |
+=================+
^
|
+------------------------+
| server instrumentation |
+------------------------+
| ^
V |
+----------------------+
| configuration |
| datastore |
+----------------------+
]]>
</artwork>
</figure>
</t>
<t>
The generation of a notification for a specific subscription
<xref target="RFC5277"/> is authorized by following these
steps:
<list style="numbers">
<t>
If the "enable-nacm" leaf is set to "false", then the
notification is permitted.
</t>
<t>
If the session is identified as a recovery session,
then the notification is permitted.
</t>
<t>
If the notification is the NETCONF
<replayComplete> or <notificationComplete>
event type <xref target="RFC5277"/>, then
the notification is permitted.
</t>
<t>
Check all the "group" entries for ones that contain a
"user-name" entry that equals the username for the
session making the request. If the
"enable-external-groups" leaf is "true", add to these
groups the set of groups provided by the transport layer.
</t>
<t>
If no groups are found, continue with step 10.
</t>
<t>
Process all rule-list entries, in the order
they appear in the configuration. If a
rule-list's "group" leaf-list does not match any
of the user's groups, proceed to the next rule-list entry.
</t>
<t>
For each rule-list entry found, process all rules, in
order, until a rule that matches the requested
access operation
is found. A rule matches if all of the following
criteria are met:
<list style="symbols">
<t>
The rule's "module-name" leaf is "*" or equals the
name of the YANG module where the notification
is defined.
</t>
<!-- errata 3409 applied below -->
<t>
The rule does not have a "rule-type" defined or the
"rule-type" is "notification" and the
"notification-name" is "*" or equals the name of the
notification.
</t>
<t>
The rule's "access-operations" leaf has the "read" bit
set or has the special value "*".
</t>
</list>
</t>
<t>
If a matching rule is found, then the "action" leaf
is checked. If it is equal to "permit", then permit the
notification; otherwise, drop the notification for the
associated subscription.
</t>
<t>
Otherwise, no matching rule was found in any rule-list
entry.
</t>
<t anchor="notif-default">
If the requested notification is defined in a
YANG module
advertised in the server capabilities and the
"notification" statement contains a
"nacm:default-deny-all" statement, then the notification is
dropped for the associated subscription.
</t>
<t>
If the "read-default" leaf is set to "permit", then
permit the notification; otherwise, drop the notification
for the associated subscription.
</t>
</list>
</t>
</section>
</section>
<section title="Data Model Definitions" anchor="DM">
<section title="Data Organization">
<t>
The following diagram highlights the contents
and structure of the NACM YANG module.
</t>
<figure>
<artwork><![CDATA[
module: ietf-netconf-acm
+--rw nacm
+--rw enable-nacm? boolean
+--rw read-default? action-type
+--rw write-default? action-type
+--rw exec-default? action-type
+--rw enable-external-groups? boolean
+--ro denied-operations yang:zero-based-counter32
+--ro denied-data-writes yang:zero-based-counter32
+--ro denied-notifications yang:zero-based-counter32
+--rw groups
| +--rw group* [name]
| +--rw name group-name-type
| +--rw user-name* user-name-type
+--rw rule-list* [name]
+--rw name string
+--rw group* union
+--rw rule* [name]
+--rw name string
+--rw module-name? union
+--rw (rule-type)?
| +--:(protocol-operation)
| | +--rw rpc-name? union
| +--:(notification)
| | +--rw notification-name? union
| +--:(data-node)
| +--rw path node-instance-identifier
+--rw access-operations? union
+--rw action action-type
+--rw comment? string
]]></artwork>
</figure>
</section>
<section title="YANG Module">
<t>
The following YANG module specifies
the normative NETCONF content that MUST
by supported by the server.
</t>
<t>
The "ietf-netconf-acm" YANG module imports typedefs from <xref
target="RFC6991"/>.
</t>
<t>
<figure anchor="YANG_module">
<!-- errata 3862 applied in matchall-string-type below -->
<!-- errata 3863 applied in group-name-type below -->
<artwork><![CDATA[
<CODE BEGINS> file "ietf-netconf-acm@2016-08-26.yang"
module ietf-netconf-acm {
namespace "urn:ietf:params:xml:ns:yang:ietf-netconf-acm";
prefix "nacm";
import ietf-yang-types {
prefix yang;
}
organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
Author: Andy Bierman
<mailto:andy@yumaworks.com>
Author: Martin Bjorklund
<mailto:mbj@tail-f.com>";
description
"NETCONF Access Control Model.
Copyright (c) 2012, 2016 IETF Trust and the persons
identified as authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD
License set forth in Section 4.c of the IETF Trust's
Legal Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
revision "2016-08-26" {
description
"Second version";
reference
"RFC XXXX: Network Configuration Protocol (NETCONF)
Access Control Model";
}
revision "2012-02-22" {
description
"Initial version";
reference
"RFC 6536: Network Configuration Protocol (NETCONF)
Access Control Model";
}
/*
* Extension statements
*/
extension default-deny-write {
description
"Used to indicate that the data model node
represents a sensitive security system parameter.
If present, and the NACM module is enabled (i.e.,
/nacm/enable-nacm object equals 'true'), the NETCONF server
will only allow the designated 'recovery session' to have
write access to the node. An explicit access control rule is
required for all other users.
The 'default-deny-write' extension MAY appear within a data
definition statement. It is ignored otherwise.";
}
extension default-deny-all {
description
"Used to indicate that the data model node
controls a very sensitive security system parameter.
If present, and the NACM module is enabled (i.e.,
/nacm/enable-nacm object equals 'true'), the NETCONF server
will only allow the designated 'recovery session' to have
read, write, or execute access to the node. An explicit
access control rule is required for all other users.
The 'default-deny-all' extension MAY appear within a data
definition statement, 'rpc' statement, or 'notification'
statement. It is ignored otherwise.";
}
/*
* Derived types
*/
typedef user-name-type {
type string {
length "1..max";
}
description
"General Purpose Username string.";
}
typedef matchall-string-type {
type string {
pattern '\*';
}
description
"The string containing a single asterisk '*' is used
to conceptually represent all possible values
for the particular leaf using this data type.";
}
typedef access-operations-type {
type bits {
bit create {
description
"Any protocol operation that creates a
new data node.";
}
bit read {
description
"Any protocol operation or notification that
returns the value of a data node.";
}
bit update {
description
"Any protocol operation that alters an existing
data node.";
}
bit delete {
description
"Any protocol operation that removes a data node.";
}
bit exec {
description
"Execution access to the specified protocol operation.";
}
}
description
"NETCONF Access Operation.";
}
typedef group-name-type {
type string {
length "1..max";
pattern '[^\*].*';
}
description
"Name of administrative group to which
users can be assigned.";
}
typedef action-type {
type enumeration {
enum permit {
description
"Requested action is permitted.";
}
enum deny {
description
"Requested action is denied.";
}
}
description
"Action taken by the server when a particular
rule matches.";
}
typedef node-instance-identifier {
type yang:xpath1.0;
description
"Path expression used to represent a special
data node, action, or notification instance identifier
string.
A node-instance-identifier value is an
unrestricted YANG instance-identifier expression.
All the same rules as an instance-identifier apply
except predicates for keys are optional. If a key
predicate is missing, then the node-instance-identifier
represents all possible server instances for that key.
This XPath expression is evaluated in the following context:
o The set of namespace declarations are those in scope on
the leaf element where this type is used.
o The set of variable bindings contains one variable,
'USER', which contains the name of the user of the current
session.
o The function library is the core function library, but
note that due to the syntax restrictions of an
instance-identifier, no functions are allowed.
o The context node is the root node in the data tree.
The accessible tree includes actions and notifications tied to
data nodes.";
}
/*
* Data definition statements
*/
container nacm {
nacm:default-deny-all;
description
"Parameters for NETCONF Access Control Model.";
leaf enable-nacm {
type boolean;
default true;
description
"Enables or disables all NETCONF access control
enforcement. If 'true', then enforcement
is enabled. If 'false', then enforcement
is disabled.";
}
leaf read-default {
type action-type;
default "permit";
description
"Controls whether read access is granted if
no appropriate rule is found for a
particular read request.";
}
leaf write-default {
type action-type;
default "deny";
description
"Controls whether create, update, or delete access
is granted if no appropriate rule is found for a
particular write request.";
}
leaf exec-default {
type action-type;
default "permit";
description
"Controls whether exec access is granted if no appropriate
rule is found for a particular protocol operation request.";
}
leaf enable-external-groups {
type boolean;
default true;
description
"Controls whether the server uses the groups reported by the
NETCONF transport layer when it assigns the user to a set of
NACM groups. If this leaf has the value 'false', any group
names reported by the transport layer are ignored by the
server.";
}
leaf denied-operations {
type yang:zero-based-counter32;
config false;
mandatory true;
description
"Number of times since the server last restarted that a
protocol operation request was denied.";
}
leaf denied-data-writes {
type yang:zero-based-counter32;
config false;
mandatory true;
description
"Number of times since the server last restarted that a
protocol operation request to alter
a configuration datastore was denied.";
}
leaf denied-notifications {
type yang:zero-based-counter32;
config false;
mandatory true;
description
"Number of times since the server last restarted that
a notification was dropped for a subscription because
access to the event type was denied.";
}
container groups {
description
"NETCONF Access Control Groups.";
list group {
key name;
description
"One NACM Group Entry. This list will only contain
configured entries, not any entries learned from
any transport protocols.";
leaf name {
type group-name-type;
description
"Group name associated with this entry.";
}
leaf-list user-name {
type user-name-type;
description
"Each entry identifies the username of
a member of the group associated with
this entry.";
}
}
}
list rule-list {
key "name";
ordered-by user;
description
"An ordered collection of access control rules.";
leaf name {
type string {
length "1..max";
}
description
"Arbitrary name assigned to the rule-list.";
}
leaf-list group {
type union {
type matchall-string-type;
type group-name-type;
}
description
"List of administrative groups that will be
assigned the associated access rights
defined by the 'rule' list.
The string '*' indicates that all groups apply to the
entry.";
}
list rule {
key "name";
ordered-by user;
description
"One access control rule.
Rules are processed in user-defined order until a match is
found. A rule matches if 'module-name', 'rule-type', and
'access-operations' match the request. If a rule
matches, the 'action' leaf determines if access is granted
or not.";
leaf name {
type string {
length "1..max";
}
description
"Arbitrary name assigned to the rule.";
}
leaf module-name {
type union {
type matchall-string-type;
type string;
}
default "*";
description
"Name of the module associated with this rule.
This leaf matches if it has the value '*' or if the
object being accessed is defined in the module with the
specified module name.";
}
choice rule-type {
description
"This choice matches if all leafs present in the rule
match the request. If no leafs are present, the
choice matches all requests.";
case protocol-operation {
leaf rpc-name {
type union {
type matchall-string-type;
type string;
}
description
"This leaf matches if it has the value '*' or if
its value equals the requested protocol operation
name.";
}
}
case notification {
leaf notification-name {
type union {
type matchall-string-type;
type string;
}
description
"This leaf matches if it has the value '*' or if its
value equals the requested notification name.";
}
}
case data-node {
leaf path {
type node-instance-identifier;
mandatory true;
description
"Data Node Instance Identifier associated with the
data node controlled by this rule.
Configuration data or state data instance
identifiers start with a top-level data node. A
complete instance identifier is required for this
type of path value.
The special value '/' refers to all possible
datastore contents.";
}
}
}
leaf access-operations {
type union {
type matchall-string-type;
type access-operations-type;
}
default "*";
description
"Access operations associated with this rule.
This leaf matches if it has the value '*' or if the
bit corresponding to the requested operation is set.";
}
leaf action {
type action-type;
mandatory true;
description
"The access control action associated with the
rule. If a rule is determined to match a
particular request, then this object is used
to determine whether to permit or deny the
request.";
}
leaf comment {
type string;
description
"A textual description of the access rule.";
}
}
}
}
}
<CODE ENDS>
]]></artwork>
</figure>
</t>
</section>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>
This document registers one URI in "The IETF XML Registry".
Following the format in <xref target="RFC3688"/>,
the following has been registered.
</t>
<t>
<figure>
<artwork><![CDATA[ URI: urn:ietf:params:xml:ns:yang:ietf-netconf-acm
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace.
]]></artwork>
</figure>
</t>
<t>
This document registers one module in the "YANG Module Names"
registry. Following the format in <xref target="RFC6020" />,
the following has been registered.
<figure>
<artwork><![CDATA[ Name: ietf-netconf-acm
Namespace: urn:ietf:params:xml:ns:yang:ietf-netconf-acm
Prefix: nacm
reference: RFC 6536
]]></artwork>
</figure>
</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>
This entire document discusses access control
requirements and mechanisms for restricting
NETCONF protocol behavior within a given session.
</t>
<t>
This section highlights the issues for an administrator
to consider when configuring a NETCONF server with NACM.
</t>
<section title="NACM Configuration and Monitoring Considerations">
<t>
Configuration of the access control system is
highly sensitive to system security. A server may
choose not to allow any user configuration to
some portions of it, such as the global security level
or the groups that allowed access to system resources.
</t>
<t>
By default, NACM enforcement is enabled.
By default, "read" access to all datastore contents is enabled
(unless "nacm:default-deny-all" is specified for the data definition),
and "exec" access is enabled for safe protocol operations.
An administrator needs to ensure that NACM is enabled
and also decide if the default access parameters are
set appropriately. Make sure the following data nodes
are properly configured:
<list style="symbols">
<t>/nacm/enable-nacm (default "true")</t>
<t>/nacm/read-default (default "permit")</t>
<t>/nacm/write-default (default "deny")</t>
<t>/nacm/exec-default (default "permit")</t>
</list>
</t>
<t>
An administrator needs to restrict write access to all
configurable objects within this data model.
</t>
<t>
If write access is allowed for configuration of
access control rules, then care needs to be taken
not to disrupt the access control enforcement.
For example, if the NACM access control rules are edited directly
within the running configuration datastore (i.e.,
:writable-running capability is supported and used),
then care needs to be taken not to allow unintended
access while the edits are being done.
</t>
<t>
An administrator needs to make sure that
the translation from a transport- or implementation-dependent
user identity to a NACM username is unique
and correct.
This requirement is specified in detail in Section 2.2
of <xref target="RFC6241"/>.
</t>
<t>
An administrator needs to be aware that the YANG data structures
representing access control rules (/nacm/rule-list
and /nacm/rule-list/rule)
are ordered by the client. The server will evaluate the
access control rules according to their relative conceptual order
within the running datastore configuration.
</t>
<t>
Note that the /nacm/groups data structure contains
the administrative group names used by the server.
These group names may be configured locally and/or
provided through an external protocol, such as RADIUS
<xref target="RFC2865"/><xref target="RFC5607"/>.
</t>
<t>
An administrator needs to be aware of the security properties
of any external protocol used by the NETCONF transport layer
to determine group names. For example, if this protocol does
not protect against man-in-the-middle attacks, an attacker
might be able to inject group names that are configured in
NACM, so that a user gets more permissions than it should.
In such cases, the administrator may wish to disable the
usage of such group names, by setting
/nacm/enable-external-groups to "false".
</t>
<t>
An administrator needs to restrict read access to the
following objects within this data model, as they reveal
access control configuration that could be considered
sensitive.
<list style="symbols">
<t>/nacm/enable-nacm</t>
<t>/nacm/read-default</t>
<t>/nacm/write-default</t>
<t>/nacm/exec-default</t>
<t>/nacm/enable-external-groups</t>
<t>/nacm/groups</t>
<t>/nacm/rule-list</t>
</list>
</t>
</section>
<section title="General Configuration Issues">
<t>
There is a risk that invocation of
non-standard protocol operations will have undocumented side effects.
An administrator needs to construct access control rules
such that the configuration datastore is protected
from such side effects.
</t>
<t>
It is possible for a session with some write access
(e.g., allowed to invoke <edit-config>),
but without any access to a particular datastore subtree
containing sensitive data, to determine the presence
or non-presence of that data.
This can be done by repeatedly issuing
some sort of edit request (create, update, or delete)
and possibly receiving "access-denied" errors in response.
These "fishing" attacks can identify the presence or
non-presence of specific sensitive data even without
the "error-path" field being present within the <rpc-error>
response.
</t>
<t>
It may be possible for the set of NETCONF capabilities
on the server to change over time. If so, then there is a risk
that new protocol operations, notifications, and/or
datastore content have been added to the device.
An administrator needs to be sure the access control
rules are correct for the new content in this case.
Mechanisms to detect NETCONF capability changes on
a specific device are outside the scope of this document.
</t>
<t>
It is possible that the data model definition itself
(e.g., YANG when-stmt) will help an unauthorized session
determine the presence or even value of sensitive data nodes
by examining the presence and values of different data nodes.
</t>
<t>
There is a risk that non-standard protocol operations, or
even the standard <get> protocol operation, may
return data that "aliases" or "copies" sensitive data
from a different data object. There may simply be
multiple data model definitions that expose
or even configure the same underlying system
instrumentation.
</t>
<t>
A data model may contain external keys
(e.g., YANG leafref), which expose values
from a different data structure.
An administrator needs to
be aware of sensitive data models that contain leafref nodes.
This entails finding all the leafref objects that
"point" at the sensitive data (i.e., "path-stmt" values) that
implicitly or explicitly include the sensitive data node.
</t>
<t>
It is beyond the scope of this document to define access
control enforcement
procedures for underlying device instrumentation that may
exist to support the NETCONF server operation. An administrator
can identify each protocol operation that the server provides
and decide if it needs any access control applied to it.
</t>
<t>
This document incorporates the optional use of a recovery session
mechanism, which can be used to bypass access control
enforcement in emergencies, such as NACM configuration errors
that disable all access to the server.
The configuration and identification of such
a recovery session mechanism are implementation-specific
and outside the scope of this document.
An administrator needs to be aware of any recovery session
mechanisms available on the device and make sure they
are used appropriately.
</t>
<t>
It is possible for a session to disrupt configuration
management, even without any write access to the configuration,
by locking the datastore. This may be done to ensure all or
part of the configuration remains stable while it is being
retrieved, or it may be done as a "denial-of-service" attack.
There is no way for the server to know the difference.
An administrator may wish to
restrict "exec" access to the following protocol operations:
<list style="symbols">
<t><lock></t>
<t><unlock></t>
<t><partial-lock></t>
<t><partial-unlock></t>
</list>
</t>
</section>
<section title="Data Model Design Considerations">
<t>
Designers need to clearly identify any sensitive data,
notifications, or protocol operations defined within a YANG
module. For such definitions, a "nacm:default-deny-write" or
"nacm:default-deny-all" statement ought to be present, in
addition to a clear description of the security risks.
</t>
<t>
Protocol operations need to be properly documented by the
data model designer, so it is clear to administrators what
data nodes (if any) are affected by the protocol operation
and what information (if any) is returned in the
<rpc-reply> message.
</t>
<t>
Data models ought to be designed so that different access
levels for input parameters to protocol operations are not required.
Use of generic protocol operations should be avoided, and if different access levels
are needed, separate
protocol operations should be defined instead.
</t>
</section>
</section>
</section>
</middle>
<back>
<references title="Normative References">
&rfc2119;
&rfc3688;
&rfc5277;
&rfc6020;
&rfc6241;
&rfc6991;
&rfc7950;
&I-D.ietf-netconf-restconf;
</references>
<references title="Informative References">
&rfc2865;
&rfc5607;
</references>
<section title="Usage Examples">
<t>
The following XML snippets are provided as examples only,
to demonstrate how NACM can be configured to perform
some access control tasks.
</t>
<section title="<groups> Example">
<t>
There needs to be at least one <group> entry
in order for any of the access control rules
to be useful.
</t>
<t>
The following XML shows arbitrary groups
and is not intended to represent any particular
use case.
</t>
<t>
<figure>
<artwork><![CDATA[
<nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
<groups>
<group>
<name>admin</name>
<user-name>admin</user-name>
<user-name>andy</user-name>
</group>
<group>
<name>limited</name>
<user-name>wilma</user-name>
<user-name>bam-bam</user-name>
</group>
<group>
<name>guest</name>
<user-name>guest</user-name>
<user-name>guest@example.com</user-name>
</group>
</groups>
</nacm>
]]>
</artwork>
</figure>
</t>
<t>
This example shows three groups:
<list style="hanging">
<t hangText="admin:">
The "admin" group contains two users named "admin" and "andy".
</t>
<t hangText="limited:">
The "limited" group contains two users named
"wilma" and "bam-bam".
</t>
<t hangText="guest:">
The "guest" group contains two users named
"guest" and "guest@example.com".
</t>
</list>
</t>
</section>
<section title="Module Rule Example">
<t>
Module rules are used to control access to all the content
defined in a specific module. A module rule has the
<module-name> leaf set, but no case in the "rule-type"
choice.
</t>
<t>
<figure>
<artwork><![CDATA[
<nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
<rule-list>
<name>guest-acl</name>
<group>guest</group>
<rule>
<name>deny-ncm</name>
<module-name>ietf-netconf-monitoring</module-name>
<access-operations>*</access-operations>
<action>deny</action>
<comment>
Do not allow guests any access to the NETCONF
monitoring information.
</comment>
</rule>
</rule-list>
<rule-list>
<name>limited-acl</name>
<group>limited</group>
<rule>
<name>permit-ncm</name>
<module-name>ietf-netconf-monitoring</module-name>
<access-operations>read</access-operations>
<action>permit</action>
<comment>
Allow read access to the NETCONF
monitoring information.
</comment>
</rule>
<rule>
<name>permit-exec</name>
<module-name>*</module-name>
<access-operations>exec</access-operations>
<action>permit</action>
<comment>
Allow invocation of the
supported server operations.
</comment>
</rule>
</rule-list>
<rule-list>
<name>admin-acl</name>
<group>admin</group>
<rule>
<name>permit-all</name>
<module-name>*</module-name>
<access-operations>*</access-operations>
<action>permit</action>
<comment>
Allow the admin group complete access to all
operations and data.
</comment>
</rule>
</rule-list>
</nacm>
]]>
</artwork>
</figure>
</t>
<t>
This example shows four module rules:
<list style="hanging">
<t hangText="deny-ncm:">
This rule prevents the "guest" group from
reading any monitoring information in
the "ietf-netconf-monitoring" YANG module.
</t>
<t hangText="permit-ncm:">
This rule allows the "limited" group to read the
"ietf-netconf-monitoring" YANG module.
</t>
<t hangText="permit-exec:">
This rule allows the "limited" group to invoke any
protocol operation supported by the server.
</t>
<t hangText="permit-all:">
This rule allows the "admin" group complete access
to all content in the server. No subsequent rule
will match for the "admin" group because of this
module rule.
</t>
</list>
</t>
</section>
<section title="Protocol Operation Rule Example">
<t>
Protocol operation rules are used to control access to
a specific protocol operation.
</t>
<t>
<figure>
<artwork><![CDATA[
<nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
<rule-list>
<name>guest-limited-acl</name>
<group>limited</group>
<group>guest</group>
<rule>
<name>deny-kill-session</name>
<module-name>ietf-netconf</module-name>
<rpc-name>kill-session</rpc-name>
<access-operations>exec</access-operations>
<action>deny</action>
<comment>
Do not allow the limited or guest group
to kill another session.
</comment>
</rule>
<rule>
<name>deny-delete-config</name>
<module-name>ietf-netconf</module-name>
<rpc-name>delete-config</rpc-name>
<access-operations>exec</access-operations>
<action>deny</action>
<comment>
Do not allow limited or guest group
to delete any configurations.
</comment>
</rule>
</rule-list>
<rule-list>
<name>limited-acl</name>
<group>limited</group>
<rule>
<name>permit-edit-config</name>
<module-name>ietf-netconf</module-name>
<rpc-name>edit-config</rpc-name>
<access-operations>exec</access-operations>
<action>permit</action>
<comment>
Allow the limited group to edit the configuration.
</comment>
</rule>
</rule-list>
</nacm>
]]>
</artwork>
</figure>
</t>
<t>
This example shows three protocol operation rules:
<list style="hanging">
<t hangText="deny-kill-session:">
This rule prevents the "limited" or "guest" groups
from invoking the NETCONF
<kill-session> protocol operation.
</t>
<t hangText="deny-delete-config:">
This rule prevents the "limited" or "guest" groups
from invoking the NETCONF
<delete-config> protocol operation.
</t>
<t hangText="permit-edit-config:">
This rule allows the "limited" group
to invoke the NETCONF
<edit-config> protocol operation.
This rule will have no real effect
unless the "exec-default" leaf is set to "deny".
</t>
</list>
</t>
</section>
<section title="Data Node Rule Example">
<t>
Data node rules are used to control access to
specific (config and non-config) data nodes
within the NETCONF content provided by the server.
</t>
<t>
<figure>
<artwork><![CDATA[
<nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
<rule-list>
<name>guest-acl</name>
<group>guest</group>
<rule>
<name>deny-nacm</name>
<path xmlns:n="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
/n:nacm
</path>
<access-operations>*</access-operations>
<action>deny</action>
<comment>
Deny the guest group any access to the /nacm data.
</comment>
</rule>
</rule-list>
<rule-list>
<name>limited-acl</name>
<group>limited</group>
<rule>
<name>permit-acme-config</name>
<path xmlns:acme="http://example.com/ns/netconf">
/acme:acme-netconf/acme:config-parameters
</path>
<access-operations>
read create update delete
</access-operations>
<action>permit</action>
<comment>
Allow the limited group complete access to the acme
NETCONF configuration parameters. Showing long form
of 'access-operations' instead of shorthand.
</comment>
</rule>
</rule-list>
<rule-list>
<name>guest-limited-acl</name>
<group>guest</group>
<group>limited</group>
<rule>
<name>permit-dummy-interface</name>
<path xmlns:acme="http://example.com/ns/itf">
/acme:interfaces/acme:interface[acme:name='dummy']
</path>
<access-operations>read update</access-operations>
<action>permit</action>
<comment>
Allow the limited and guest groups read
and update access to the dummy interface.
</comment>
</rule>
</rule-list>
<rule-list>
<name>admin-acl</name>
<group>admin</group>
<rule>
<name>permit-interface</name>
<path xmlns:acme="http://example.com/ns/itf">
/acme:interfaces/acme:interface
</path>
<access-operations>*</access-operations>
<action>permit</action>
<comment>
Allow admin full access to all acme interfaces.
</comment>
</rule>
</rule-list>
</nacm>
]]>
</artwork>
</figure>
</t>
<t>
This example shows four data node rules:
<list style="hanging">
<t hangText="deny-nacm:">
This rule denies the "guest" group
any access to the <nacm> subtree.
Note that the default namespace is only
applicable because this subtree is defined
in the same namespace as the <data-rule>
element.
</t>
<t hangText="permit-acme-config:">
This rule gives the "limited" group
read-write access to the acme <config-parameters>.
</t>
<t hangText="permit-dummy-interface:">
This rule gives the "limited" and "guest" groups
read-update access to the acme <interface>
entry named "dummy". This entry cannot be created or
deleted by these groups, just altered.
</t>
<t hangText="permit-interface:">
This rule gives the "admin" group
read-write access to all acme <interface>
entries.
</t>
</list>
</t>
</section>
<section title="Notification Rule Example">
<t>
Notification rules are used to control access to
a specific notification event type.
</t>
<t>
<figure>
<artwork><![CDATA[
<nacm xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-acm">
<rule-list>
<name>sys-acl</name>
<group>limited</group>
<group>guest</group>
<rule>
<name>deny-config-change</name>
<module-name>acme-system</module-name>
<notification-name>sys-config-change</notification-name>
<access-operations>read</access-operations>
<action>deny</action>
<comment>
Do not allow the guest or limited groups
to receive config change events.
</comment>
</rule>
</rule-list>
</nacm>
]]>
</artwork>
</figure>
</t>
<t>
This example shows one notification rule:
<list style="hanging">
<t hangText="deny-config-change:">
This rule prevents the "limited" or "guest" groups
from receiving the
acme <sys-config-change> event type.
</t>
</list>
</t>
</section>
</section>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-24 08:58:26 |