Network Working Group K. Narayan
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track D. Nelson
Expires: November 16, 2010 Elbrys Networks, Inc.
R. Presuhn, Ed.
None
May 15, 2010
Extensions to the View-based Access Control Model for use with RADIUS
draft-ietf-isms-radius-vacm-06.txt
Abstract
This memo defines a portion of the Management Information Base (MIB)
for use with network management protocols. In particular, it
describes a backward-compatible supplement to the View-based Access
Control Model (VACM) for version 3 of the Simple Network Management
Protocol (SNMPv3) for use with the Remote Authentication Dial-In User
Service (RADIUS) or other Authentication, Authorization, and
Accounting (AAA) services to provide authorization of MIB database
access, and defines objects for managing this supplement. It is
intended to be used in conjunction with session-oriented secure SNMP
Transport Models that facilitate RADIUS authentication, such as the
Secure Shell Transport Model.
Comments are solicited and should be addressed to the working group's
mailing list at isms@ietf.org.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 16, 2010.
Copyright Notice
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Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The Internet-Standard Management Framework . . . . . . . . . . 4
3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. System Block Diagram . . . . . . . . . . . . . . . . . . . 4
4.2. Using RADIUS with SNMP . . . . . . . . . . . . . . . . . . 5
4.3. Applicability . . . . . . . . . . . . . . . . . . . . . . 6
5. Structure of the MIB Module . . . . . . . . . . . . . . . . . 7
5.1. Textual Conventions . . . . . . . . . . . . . . . . . . . 7
5.2. The Table Structure . . . . . . . . . . . . . . . . . . . 7
6. Relationship to Other MIB Modules . . . . . . . . . . . . . . 7
6.1. Relationship to the VACM MIB . . . . . . . . . . . . . . . 8
6.2. MIB modules required for IMPORTS . . . . . . . . . . . . . 8
7. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 8
7.1. Sequencing Requirements . . . . . . . . . . . . . . . . . 8
7.2. Actions Upon Session Establishment Indication . . . . . . 9
7.2.1. Creation of Entries in extVacmSecurityToGroupTable . . 9
7.2.2. Creation of Entries in vacmSecurityToGroupTable . . . 9
7.2.3. Update of vacmGroupName . . . . . . . . . . . . . . . 10
7.3. Actions Upon Session Termination Indication . . . . . . . 10
7.3.1. Deletion of Entries from
extVacmSecurityToGroupTable . . . . . . . . . . . . . 10
7.3.2. Deletion of Entries from vacmSecurityToGroupTable . . 11
8. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 11
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 17
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
12.1. Normative References . . . . . . . . . . . . . . . . . . . 17
12.2. Informative References . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
This memo specifies an integration of several protocols to
operationally simplify the administration of the access rights
granted to users of network management data. It functions to
dynamically provision selected MIB objects associated with VACM
[RFC3415] based on information received from RADIUS or other AAA
service. It requires no changes to the Abstract Service Interface
for the Access Control Subsystem, and requires no changes to the
Elements of Procedure for VACM. It provides a MIB module that
reflects the information received from the AAA service, as well as
the elements of procedure for maintaining that information and the
corresponding updates to VACM data.
In this environment:
o The View-Based Access Control Model (VACM) [RFC3415] provides a
means to manage users' access rights to management information
accessed using SNMP.
o The Simple Network Management Protocol version 3 (SNMPv3) provides
message security services through the Security Subsystem.
o The Transport Subsystem for the Simple Network Management Protocol
[RFC5590] defines a Transport Subsystem.
o The Transport Security Model for SNMP [RFC5591] defines a
Transport Security Model.
o The Secure Shell Transport Model for SNMP [RFC5592] defines a
Secure Shell Transport Model.
o RADIUS Usage for Simple Network Management Protocol (SNMP)
Transport Models [RFC5608] defines a method for authenticating
SNMPv3 users via RADIUS.
It is possible to authenticate SNMPv3 messages via a RADIUS when
those messages are sent over the SSH transport. As originally
envisioned, VACM authorizes a given SNMP transaction using on-device,
pre-existing authorization configuration. In order to leverage a
centralized RADIUS service to its full extent, the access control
decision in the Access Control Subsystem needs to be able to make use
of authorization information received from RADIUS as well. This memo
defines a supplement to the View-based Access Control Model to obtain
authorization information for an authenticated principal, from RADIUS
or an equivalent AAA service when used with a Transport Security
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Model.
Additional introductory material on the RADIUS operational model and
RADIUS usage with SNMP may be found in Sections 1.3 and 1.5 of
[RFC5608].
It is important to understand the SNMP architecture and the
terminology of the architecture to understand where the View-based
Access Control Model supplement described in this memo fits into the
architecture and how it interacts with other subsystems and models
within the architecture. It is expected that reader will have also
read and understood RFC3411 [RFC3411], RFC3412 [RFC3412], RFC3413
[RFC3413], RFC3415 [RFC3415]and RFC3418 [RFC3418]. As this memo
describes a supplement to VACM, a thorough understanding of RFC3415
[RFC3415] is assumed.
2. The Internet-Standard Management Framework
For a detailed overview of the documents that describe the current
Internet-Standard Management Framework, please refer to section 7 of
RFC 3410 [RFC3410].
Managed objects are accessed via a virtual information store, termed
the Management Information Base or MIB. MIB objects are generally
accessed through the Simple Network Management Protocol (SNMP).
Objects in the MIB are defined using the mechanisms defined in the
Structure of Management Information (SMI). This memo specifies a MIB
module that is compliant to the SMIv2, which is described in STD 58,
RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580
[RFC2580].
3. Conventions
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 RFC 2119 [RFC2119].
4. Overview
4.1. System Block Diagram
A block diagram of the major system components referenced in this
document may be useful to understanding the text that follows.
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+--------+
+......................... |RADIUS |....+
. |Server | .
Shared +--------+ .
User | .
Credentials RADIUS | Shared
. | RADIUS
. | Secret
. | .
+-------------+ +-----------------+
| Network | | RADIUS Client / |
| Management | SNMP | SNMP Engine / |
| Application |------------------| Network Device |
+-------------+ SSH +-----------------+
Block Diagram
This diagram illustrates that a network management application
communicates with a network device, the managed entity, using, for
example, SNMP over SSH. The network device uses RADIUS to
communicate with a RADIUS Server to authenticate the network
management application (or the user whose credentials that
application provides) and to obtain authorization information related
to access via SNMP for purpose of device management. Other secure
transport protocols might be used instead of SSH, and other AAA
services might be used instead of RADIUS.
4.2. Using RADIUS with SNMP
There are two use cases for RADIUS support of management access via
SNMP. These are (a) service authorization and (b) access control
authorization. The former is discussed in detail in [RFC5608]. The
second use case is the subject of this document. This document
describes how RADIUS attributes and messages are applied to the
specific application area of SNMP Access Control Models, and VACM in
particular.
The RFC 3411 SNMP architecture maintains strong modularity and
separation of concerns, extending to separating user identity
(authentication) from user database access rights (authorization).
The former is the business of the Security Subsystem and the latter
is the business of the Access Control Subsystem. RADIUS, on the
other hand, allows for no such separation of authorization from
authentication. In order to use RADIUS with SNMP, binding of user
authentication to user authorization must be achieved, without
violating the modularity of the RFC 3411 SNMP architecture.
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RADIUS does support a limited form of Authorize-Only operations. The
RADIUS "Authorize Only" Service-Type Attribute can be specified in an
Access-Request message, but only when accompanied by a RADIUS State
Attribute, which contains an implementation-specific "cookie"
representing the successful outcome of a previous authentication
transaction. For that reason, it is not possible to completely
separate the use of RADIUS by the Access Control Subsystem from the
use of RADIUS by other subsystems. This suggests that the most
straightforward approach is to leverage the existing RADIUS usage, as
documented in [RFC5608], and a session identifier, such as
tmSessionID [RFC5590]. How this information is communicated within
an implementation is implementation-dependent.
The operative use case assumption here is that roles within an
organization, which are reflected in VACM as groups and rules, change
infrequently, while the users assigned to those roles change much
more frequently. This memo describes how the user-to-role (group)
mapping can be delegated to the RADIUS server, avoiding the need to
re-provision managed devices as users are added, deleted, or assigned
new roles in an organization.
This memo assumes that the detailed access control policies are pre-
configured in VACM, and does not attempt to address the question of
how the policy associated with a given role is put in place.
The only additional information obtained from the AAA service is the
mapping of the authenticated user's identifier to a specific role (or
"group" in VACM terminology) in the access control policy. Dynamic
user authorization for MIB database access control, as defined
herein, is limited to mapping the authenticated user to a group,
which in turn is mapped to the pre-existing rules.
This memo relies on implementation-specific integration of the AAA
client for user authentication and authorization. In particular, the
implementation MUST make the RADIUS Management-Policy-Id [RFC5607]
and User-Name Attributes (or their equivalents) from the RADIUS
Access-Accept message (or equivalent) available to this function.
4.3. Applicability
Though this memo was motivated to support the use of specific
Transport Security Models, it MAY be used with other Transport
Security Models whose implementations satisfy these requirements:
o the model has a notion of "session";
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o the model uses an AAA service for sign-on service authorization;
o the model provides an indication of the establishment of a session
for a particular authenticated principal, identified using a
SecurityName, and provides the corresponding value of
vacmGroupName to be used, based on information provided by the AAA
service in use;
o the model provides an indication of the end of a session, whether
due to disconnection, termination due to timeout, or any other
reason.
Likewise, although this memo specifically refers to RADIUS, it MAY be
used with other AAA services satisfying these requirements:
o the service provides information semantically equivalent to the
RADIUS Management-Policy-ID attribute [RFC5607], which corresponds
to a GroupName;
o the service provides information semantically equivalent to the
RADIUS User-Name Attribute, which corresponds to a SecurityName.
5. Structure of the MIB Module
5.1. Textual Conventions
This MIB module makes use of the SnmpAdminString and
SnmpSecurityModel textual conventions.
5.2. The Table Structure
This MIB module defines a single table, the
extVacmSecurityToGroupTable. This table is indexed by the integer
assigned to each security model, the protocol-independent
SecurityName corresponding to a principal, and the unique identifier
of a transport model session. This index structure was chosen to
support use cases in which a given user could potentially have
multiple concurrent sessions, and to support environments in which
multiple security models might find concurrent usage.
6. Relationship to Other MIB Modules
This MIB module has a close operational relationship with the SNMP-
VIEW-BASED-ACM-MIB (more commonly known as the "VACM MIB") from
[RFC3415]. It also relies on IMPORTS from several other modules.
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6.1. Relationship to the VACM MIB
Although the MIB module defined here has a close relationship with
the VACM MIB's vacmSecurityToGroupTable, it in no way changes the
elements of procedure for VACM, nor does it affect any other tables
defined in VACM. See the elements of procedure (below) for details
of how the contents of the vacmSecurityToGroupTable are affected by
this MIB module.
6.2. MIB modules required for IMPORTS
This MIB module employs definitions from [RFC2578], [RFC2579] and
[RFC3411].
7. Elements of Procedure
The following elements of procedure are formulated in terms of two
types of events: an indication of the establishment of a secure
transport model session, and an indication that one has ended. These
events can result in the creation of entries in the
extVacmSecurityToGroupTable, which can in turn trigger creation,
update, or deletion of entries in the vacmSecurityToGroupTable.
There are various possible implementation-specific error cases not
spelled out here, such as running out of memory. By their nature,
recovery in such cases will be implementation-specific. Implementers
are advised to consider fail-safe strategies, e.g., prematurely
terminating access in preference to erroneously perpetuating access.
7.1. Sequencing Requirements
These procedures assume that a secure transport model, such as
[RFC5592], coordinates session establishment with AAA authorization.
The security model SHOULD bind principal identity to access control
policy via an external AAA server, as the Transport Security Model
does. To do otherwise potentially creates a security risk.
To ensure correct processing of SNMP PDUs, the handling of the
indication of the establishment of a session in accordance with the
elements of procedure below MUST be completed before the
IsAccessAllowed() abstract service interface is invoked for any SNMP
PDUs from that session.
To ensure correct processing of SNMP PDUs, the handling of the
indication of the termination of a session in accordance with the
elements of procedure below MUST NOT be initiated before all
invocations of the IsAccessAllowed() abstract service interface have
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completed for all SNMP PDUs from that session.
7.2. Actions Upon Session Establishment Indication
Four pieces of information are needed to process the session
establishment indication:
o the SecurityModel
o the RADIUS User-Name Attribute or equivalent
o a session identifier
o the RADIUS Management-Policy-Id Attribute or equivalent
In particular, if either the User-Name or Management-Policy-Id is
absent, invalid, or a zero-length string, no further processing of
the session establishment indication is undertaken.
7.2.1. Creation of Entries in extVacmSecurityToGroupTable
Whenever an indication arrives that a new secure transport model
session has been established, determine whether a corresponding entry
exists in the extVacmSecurityToGroupTable. If one does not, create a
new row with the columns populated as follows:
o extVacmSecurityModel = value of SnmpSecurityModel corresponding to
the security model in use
o extVacmSecurityName = RADIUS User-Name Attribute or equivalent
o extVacmTransportSessionID = unique session identifier provided by
the Secure Transport Model
o extVacmGroupName = RADIUS Management-Policy-Id Attribute or
equivalent
Otherwise, if the row already exists, update the extVacmGroupName
with the value supplied.
7.2.2. Creation of Entries in vacmSecurityToGroupTable
Whenever an entry is created in the extVacmSecurityToGroupTable, the
vacmSecurityToGroupTable is examined to determine whether a
corresponding entry exists there, using the value of
extVacmSecurityModel for vacmSecurityModel, and the value of
extVacmSecurityName for vacmSecurityName. If no corresponding entry
exists, create one, using the extVacmGroupName of the newly created
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entry to fill in vacmGroupName, using a value of "volatile" for
vacmSecurityToGroupStorageType, and a value of "active" for
vacmSecurityToGroupStatus.
If a corresponding entry already exists in the
vacmSecurityToGroupTable, and the row's StorageType is anything other
than "volatile", or the RowStatus is anything other than "active",
then a role (group) mapping for this user (principal) has already
been put in place on this system, and will not be overridden.
7.2.3. Update of vacmGroupName
Whenever the value of an instance of extVacmGroupName is updated, if
a corresponding entry exists in the vacmSecurityToGroupTable, and
vacmSecurityToGroupStorageType is "volatile" and
vacmSecurityToGroupStatus is "active", update the value of
vacmGroupName with the value from extVacmGroupName.
The operational assumption here is that if the row's StorageType is
"volatile", then this entry was probably dynamically created by this
function; an entry created by a security administrator would not
normally be given a StorageType of "volatile". If value being
provided by RADIUS (or other AAA service) is the same as what is
already there, this is a no-op. If the value is different, the new
information is understood as a more recent role (group) assignment
for the user, which should supercede the one currently held there.
7.3. Actions Upon Session Termination Indication
Whenever a RADIUS (or other AAA) authenticated secure transport model
session ends for any reason, an indication is provided to this
function. This indication MUST provide means of determining the
SecurityModel and an identifier for the session, which MUST be unique
at least within the scope of that SecurityModel. The manner in which
this occurs is implementation dependent.
7.3.1. Deletion of Entries from extVacmSecurityToGroupTable
Entries in the extVacmSecurityToGroupTable MUST NOT persist across
system reboots.
When notified that a session has been terminated, the
extVacmSecurityToGroupTable is searched for a corresponding entry.
(A "matching" entry is any entry for which the SecurityModel and
session ID match the information associated with the session
termination indication.) Any matching entries are deleted. It is
possible that no entries will match; this is not an error, and no
special processing is required in this case.
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7.3.2. Deletion of Entries from vacmSecurityToGroupTable
Whenever the last remaining row bearing a particular
(extVacmSecurityModel, extVacmSecurityName) pair is deleted from the
extVacmSecurityToGroupTable, the vacmSecurityToGroupTable is examined
for a corresponding row. If one exists, and if its StorageType is
"volatile" and its RowStatus is "active", that row MUST be deleted as
well. The mechanism to accomplish this task is implementation
specific.
8. Definitions
SNMP-EXT-VACM-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF
MODULE-IDENTITY, OBJECT-TYPE,
mib-2,
Unsigned32 FROM SNMPv2-SMI
SnmpAdminString,
SnmpSecurityModel FROM SNMP-FRAMEWORK-MIB;
snmpExtVacmMIB MODULE-IDENTITY
LAST-UPDATED "201005140000Z" -- 14 May, 2010
ORGANIZATION "ISMS Working Group"
CONTACT-INFO "WG-email: isms@ietf.org"
DESCRIPTION "The management and local datastore information
definitions for the Extended View-based Access
Control Model for SNMP.
Copyright (c) 2010 IETF Trust and the persons
identified as the document authors. 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 MIB module is part of RFC XXXX;
see the RFC itself for full legal notices."
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REVISION "201005140000Z"
DESCRIPTION "Initial version, published as RFC XXXX."
::= { mib-2 XXX }
extVacmMIBObjects OBJECT IDENTIFIER ::= { snmpExtVacmMIB 1 }
extVacmMIBConformance OBJECT IDENTIFIER ::= {snmpExtVacmMIB 2 }
extVacmSecurityToGroupTable OBJECT-TYPE
SYNTAX SEQUENCE OF ExtVacmSecurityToGroupEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "This table maps a combination of SecurityModel and
SecurityName into a GroupName, which is identifies
an access control policy for a group of principals."
::= { extVacmMIBObjects 1 }
extVacmSecurityToGroupEntry OBJECT-TYPE
SYNTAX ExtVacmSecurityToGroupEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "An entry in this table maps the combination of a
SecurityModel and SecurityName into a GroupName.
An entry corresponds to a secure transport model
session.
Entries do not persist across reboots.
When the secure transport model session is torn
down, disconnected, timed out (e.g. following the
RADIUS Session-Timeout Attribute), or otherwise
terminated for any reason, the corresponding
extVacmSecurityToGroupEntry is deleted."
INDEX {
extVacmSecurityModel,
extVacmSecurityName,
extVacmTransportSessionID
}
::= { extVacmSecurityToGroupTable 1 }
ExtVacmSecurityToGroupEntry ::= SEQUENCE
{
extVacmSecurityModel SnmpSecurityModel,
extVacmSecurityName SnmpAdminString,
extVacmTransportSessionID Unsigned32,
extVacmGroupName SnmpAdminString
}
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extVacmSecurityModel OBJECT-TYPE
SYNTAX SnmpSecurityModel(1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "The Security Model to which the session referred
to by this entry belongs.
This object cannot take the 'any' (0) value."
::= { extVacmSecurityToGroupEntry 1 }
extVacmSecurityName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(1..32))
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "The Security Name of the principal associated with
this session, provided by the Transport Model, and
represented in a Security Model independent format."
::= { extVacmSecurityToGroupEntry 2 }
extVacmTransportSessionID OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "A transport model-specific identifier of the
session. This value MUST be unique among all
of a given transport model's currently open sessions.
The value has no particular significance other
to distinguish sessions. An example of a suitable
value would be tmSessionID."
::= { extVacmSecurityToGroupEntry 3 }
extVacmGroupName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(1..32))
MAX-ACCESS read-only
STATUS current
DESCRIPTION "The name of the group to which this entry
is to belong. This information would have come
from, for example, the RADIUS Management-Policy-ID
attribute.
This group name is used to set the vacmGroupName
in the corresponding vacmSecurityToGroupEntry."
::= { extVacmSecurityToGroupEntry 4 }
-- Conformance information ******************************************
extVacmMIBCompliances
OBJECT IDENTIFIER ::= {extVacmMIBConformance 1}
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extVacmMIBGroups
OBJECT IDENTIFIER ::= {extVacmMIBConformance 2}
-- compliance statements
extVacmMIBBasicCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION "The compliance statement for SNMP engines which
implement the Extensions to the View-based Access
Control Model for use with RADIUS.
"
MODULE -- this module
MANDATORY-GROUPS { extVacmGroup }
::= { extVacmMIBCompliances 1 }
-- units of conformance
extVacmGroup OBJECT-GROUP
OBJECTS {
extVacmGroupName
}
STATUS current
DESCRIPTION "A collection of objects for supporting the use
of RADIUS to provide user / group mappings for VACM.
"
::= { extVacmMIBGroups 1 }
END
9. Security Considerations
The algorithms in this memo make heuristic use of the StorageType of
entries in the vacmSecurityToGroupTable to distinguish those
provisioned by a security administrator (which would presumably not
be configured as "volatile") from those dynamically generated. In
making this distinction, it assumes that those entries explicitly
provisioned by a security administrator and given a non-"volatile"
status are not to be dynamically over-ridden. Users of this memo
need to be aware of this operational assumption, which, while
reasonable, is not necessarily universally valid. For example, this
situation could also occur if the SNMP security administrator had
mistakenly created these non-volatile entries in error.
The design of VACM ensures that if an unknown policy (group name) is
used in the VacmSecurityToGroupTable, no access is granted. A
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consequence of this is that no matter what information is provided by
the AAA server, no user can gain SNMP access rights not already
granted to some group through the VACM configuration.
In order to ensure that the access control policy ultimately applied
as a result of the mechanisms described here is indeed the intended
policy for a given principal using a particular security model, care
needs to be applied in the mapping of the authenticated user
(principal) identity to the securityName used to make the access
control decision. Broadly speaking, there are two approaches to
ensure consistency of identity:
o Entries for the vacmSecurityToGroup table corresponding to a given
security model are created only through the operation of the
procedures described in this memo. A consequence of this would be
that all such entries would have been created using the RADIUS
User-Name (or other AAA-authenticated identity) and RADIUS
Management-Policy-Id Attribute (or equivalent).
o Administrative policy allows a matching pre-configured entry to
exist in the vacmSecurityToGroup table, i.e., an entry with the
corresponding vacmSecurityModel and with a vacmSecurityName
matching the authenticated principal's RADIUS User-Name). In this
case, administrative policy also needs to ensure consistency of
identity between each authenticated principal's RADIUS User-Name
and the administratively configured vacmSecurityName in the
vacmSecurityToGroup table row entries for that particular security
model.
In the later case, inconsistent re-use of the same name for different
entities or individuals (principals) can cause the incorrect access
control policy to be applied for the authenticated principal,
depending on whether the policy configured using SNMP, or the policy
applied using the procedures of this memo, is the intended policy.
This may result in greater or lesser access rights than the
administrative policy intended. Inadvertent mis-identification in
such cases may be undetectable by the SNMP engine or other software
elements of the managed entity.
There are no management objects defined in this MIB module that have
a MAX-ACCESS clause of read-write and/or read-create. So, if this
MIB module is implemented correctly, then there is no risk that an
intruder can alter or create any management objects of this MIB
module via direct SNMP SET operations.
Some of the readable objects in this MIB module (including some
objects with a MAX-ACCESS of not-accessible, whose values are exposed
as a result access to indexed objects) may be considered sensitive or
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vulnerable in some network environments. It is thus important to
control even GET and/or NOTIFY access to these objects and possibly
to even encrypt the values of these objects when sending them over
the network via SNMP. These are the tables and objects and their
sensitivity/vulnerability:
o extVacmSecurityToGroupTable - the entire table is potentially
sensitive, since walking the table will reveal user names,
security models in use, transport model session identifiers, and
group names.
o extVacmSecurityModel - though not-accessible, this is exposed as
an index of extVacmGroupName
o extVacmSecurityName - though not-accessible, this is exposed as an
index of extVacmGroupName
o extVacmTransportSessionID - though not-accessible, this is exposed
as an index of extVacmGroupName
o extVacmGroupName - since this identifies a security policy and
associates it with a particular user, this is potentially
sensitive.
SNMP versions prior to SNMPv3 did not include adequate security.
Even if the network itself is secure (for example by using IPsec),
even then, there is no control as to who on the secure network is
allowed to access and GET/SET (read/change/create/delete) the objects
in this MIB module.
It is RECOMMENDED that implementers consider the security features as
provided by the SNMPv3 framework (see [RFC3410], section 8),
including full support for the SNMPv3 cryptographic mechanisms (for
authentication and privacy).
Further, deployment of SNMP versions prior to SNMPv3 is NOT
RECOMMENDED. Instead, it is RECOMMENDED to deploy SNMPv3 and to
enable cryptographic security. It is then a customer/operator
responsibility to ensure that the SNMP entity giving access to an
instance of this MIB module is properly configured to give access to
the objects only to those principals (users) that have legitimate
rights to indeed GET or SET (change/create/delete) them.
10. IANA Considerations
The MIB module in this document uses the following IANA-assigned
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OBJECT IDENTIFIER values recorded in the SMI Numbers registry:
Descriptor OBJECT IDENTIFIER value
---------- -----------------------
snmpExtVacmMIB { mib-2 XXX }
Editor's Note (to be removed prior to publication): the IANA is
requested to assign a value for "XXX" under the 'mib-2' subtree and
to record the assignment in the SMI Numbers registry. When the
assignment has been made, the RFC Editor is asked to replace "XXX"
(here and in the MIB module) with the assigned value and to remove
this note.
11. Contributors
The following participants from the isms working group contributed to
the development of this document:
o Andrew Donati
o David Harrington
o Jeffrey Hutzelman
o Juergen Schoenwaelder
o Tom Petch
o Wes Hardaker
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Textual Conventions for SMIv2",
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STD 58, RFC 2579, April 1999.
[RFC2580] McCloghrie, K., Perkins, D., and J. Schoenwaelder,
"Conformance Statements for SMIv2", STD 58, RFC 2580,
April 1999.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
December 2002.
[RFC3415] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based
Access Control Model (VACM) for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3415,
December 2002.
[RFC5591] Harrington, D. and W. Hardaker, "Transport Security Model
for the Simple Network Management Protocol (SNMP)",
RFC 5591, June 2009.
[RFC5607] Nelson, D. and G. Weber, "Remote Authentication Dial-In
User Service (RADIUS) Authorization for Network Access
Server (NAS) Management", RFC 5607, July 2009.
[RFC5608] Narayan, K. and D. Nelson, "Remote Authentication Dial-In
User Service (RADIUS) Usage for Simple Network Management
Protocol (SNMP) Transport Models", RFC 5608, August 2009.
12.2. Informative References
[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.
[RFC3412] Case, J., Harrington, D., Presuhn, R., and B. Wijnen,
"Message Processing and Dispatching for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3412,
December 2002.
[RFC3413] Levi, D., Meyer, P., and B. Stewart, "Simple Network
Management Protocol (SNMP) Applications", STD 62,
RFC 3413, December 2002.
[RFC3418] Presuhn, R., "Management Information Base (MIB) for the
Simple Network Management Protocol (SNMP)", STD 62,
RFC 3418, December 2002.
[RFC5590] Harrington, D. and J. Schoenwaelder, "Transport Subsystem
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for the Simple Network Management Protocol (SNMP)",
RFC 5590, June 2009.
[RFC5592] Harrington, D., Salowey, J., and W. Hardaker, "Secure
Shell Transport Model for the Simple Network Management
Protocol (SNMP)", RFC 5592, June 2009.
Authors' Addresses
Kaushik Narayan
Cisco Systems, Inc.
10 West Tasman Drive
San Jose, CA 95134
USA
Phone: +1 408-526-8168
Email: kaushik_narayan@yahoo.com
David Nelson
Elbrys Networks, Inc.
282 Corporate Drive, Unit #1,
Portsmouth, NH 03801
USA
Phone: +1 603-570-2636
Email: d.b.nelson@comcast.net
Randy Presuhn (editor)
None
San Jose, CA 95120
USA
Email: randy_presuhn@mindspring.com
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