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 Narayan, et al. Expires November 16, 2010 [Page 1] Internet-Draft RADIUS-Enabled VACM May 2010 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 Narayan, et al. Expires November 16, 2010 [Page 2] Internet-Draft RADIUS-Enabled VACM May 2010 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 Narayan, et al. Expires November 16, 2010 [Page 3] Internet-Draft RADIUS-Enabled VACM May 2010 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. Narayan, et al. Expires November 16, 2010 [Page 4] Internet-Draft RADIUS-Enabled VACM May 2010 +--------+ +......................... |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. Narayan, et al. Expires November 16, 2010 [Page 5] Internet-Draft RADIUS-Enabled VACM May 2010 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"; Narayan, et al. Expires November 16, 2010 [Page 6] Internet-Draft RADIUS-Enabled VACM May 2010 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. Narayan, et al. Expires November 16, 2010 [Page 7] Internet-Draft RADIUS-Enabled VACM May 2010 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 Narayan, et al. Expires November 16, 2010 [Page 8] Internet-Draft RADIUS-Enabled VACM May 2010 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 Narayan, et al. Expires November 16, 2010 [Page 9] Internet-Draft RADIUS-Enabled VACM May 2010 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. Narayan, et al. Expires November 16, 2010 [Page 10] Internet-Draft RADIUS-Enabled VACM May 2010 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." Narayan, et al. Expires November 16, 2010 [Page 11] Internet-Draft RADIUS-Enabled VACM May 2010 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 } Narayan, et al. Expires November 16, 2010 [Page 12] Internet-Draft RADIUS-Enabled VACM May 2010 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} Narayan, et al. Expires November 16, 2010 [Page 13] Internet-Draft RADIUS-Enabled VACM May 2010 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 Narayan, et al. Expires November 16, 2010 [Page 14] Internet-Draft RADIUS-Enabled VACM May 2010 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 Narayan, et al. Expires November 16, 2010 [Page 15] Internet-Draft RADIUS-Enabled VACM May 2010 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 Narayan, et al. Expires November 16, 2010 [Page 16] Internet-Draft RADIUS-Enabled VACM May 2010 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", Narayan, et al. Expires November 16, 2010 [Page 17] Internet-Draft RADIUS-Enabled VACM May 2010 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 Narayan, et al. Expires November 16, 2010 [Page 18] Internet-Draft RADIUS-Enabled VACM May 2010 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 Narayan, et al. Expires November 16, 2010 [Page 19]