[NEWS] Cisco IOS Software Processing of SAA Packets

From: SecuriTeam (support_at_securiteam.com)
Date: 05/18/03

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    To: list@securiteam.com
    Date: 18 May 2003 11:05:44 +0200

    The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com
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      Cisco IOS Software Processing of SAA Packets


    The Service Assurance Agent (SAA) is the new name for the Response Time
    Reporter (RTR) feature.

    The router is vulnerable only if the RTR responder is enabled. When the
    router receives a malformed RTR packet, it will crash. RTR is disabled by
    default. Although RTR was introduced in Cisco IOSŪ Software Release 11.2,
    only the following main releases are vulnerable:
      * 12.0S, SC, ST, SL, SP, SX
      * 12.1, E, EA, EC, EX, EY
      * 12.2, DA, S
    For the complete list, please see the Software Versions and Fixes section.
    No other Cisco product is vulnerable.

    There is no workaround short of disabling the RTR responder. It is
    possible to mitigate the vulnerability by applying the access control list
    (ACL) on the router.


    Affected Products:
    This vulnerability affects the following main Cisco IOS Software releases
    (some X releases are also affected, and those details are in the Software
    Version and Fixes section).

    | Major | Vulnerable Releases |
    | Release | |
    | 12.0S | 15, 16, 17, 18, 19, 21 |
    | 12.0SC | 15, 16 |
    | 12.0SL | 15, 17, 19 |
    | 12.0ST | 16, 17, 18, 19, 20, 21 |
    | 12.0SP | 19, 20 |
    | 12.0SX | 21 |
    | 12.1 | 10, 10a, 11, 11a, 11b, 12, |
    | | 12a, 12b, 12c, 13, 14, 14.5 |
    | 12.1E | 10, 11b, 11.5 |
    | 12.1EA | 8, 9 |
    | 12.1EC | 10, 10.5 |
    | 12.1EX | 10 |
    | 12.1EY | 10 |
    | 12.2 | 6.8a, 7, 7a, 7b, 7c |
    | 12.2DA | 7, 9.4 |
    | 12.2S | 9, 10.5 |

    No other Cisco products are affected.

    The RTR feature allows you to monitor network performance, network
    resources, and applications by measuring response times and availability.
    With this feature, you can perform troubleshooting, problem notifications,
    and problem analysis based on response time reporter statistics.

    A router is vulnerable only if the RTR responder is enabled. In order to
    verify this, check the router's configuration. Execute the following
    command while logged on a router:

        Router>show rtr responder
             RTR Responder is: Enabled
             Number of control messages received: 0 Number of errors: 0
             Recent sources:
             Recent error sources:

    If you notice the line "RTR Responder is: Enabled," then you are

    Alternatively, you can use this procedure:

        Router>show ip socket
             show ip socket
             Proto Remote Port Local Port In Out Stat TTY OutputIF
              17 0 1967 0 0 89 0

    If you notice a line as in the example above where the router is listening
    to the port 1967, then you are vulnerable.

    For Cisco IOS Software, this vulnerability is documented as two Cisco Bug
    IDs: CSCdx17916 and CSCdx61997.

    By sending malformed RTR packets, it is possible to crash the router.

    Software Versions and Fixes:
    By going to the following URL, you can see a complete table of software
    versions and fixes:
    <http://www.cisco.com/warp/public/707/cisco-sa-20030515-saa.shtml#Software> http://www.cisco.com/warp/public/707/cisco-sa-20030515-saa.shtml#Software

    Obtaining Fixed Software:
    Cisco is offering free software upgrades to remedy this vulnerability for
    all affected customers. Customers may only install and expect support for
    the feature sets they have purchased. By installing, downloading,
    accessing or otherwise using such software upgrades, Customers agree to be
    bound by the terms of Cisco's software license terms found at
    http://www.cisco.com/public/sw-license-agreement.html, or as otherwise set
    forth at the Cisco Connection Online Software Center at

    Customers with contracts should obtain upgraded software through their
    regular update channels. For most customers, this means that upgrades
    should be obtained through the Software Center on Cisco's worldwide
    website at <http://www.cisco.com> http://www.cisco.com.

    Customers whose Cisco products are provided or maintained through prior or
    existing agreement with third-party support organizations such as Cisco
    Partners, authorized resellers, or service providers should contact that
    support organization for assistance with the upgrade, which should be free
    of charge.

    Customers who purchase direct from Cisco but who do not hold a Cisco
    service contract and customers who purchase through third-party vendors
    but are unsuccessful at obtaining fixed software through their point of
    sale should get their upgrades by contacting the Cisco Technical
    Assistance Center (TAC). In those cases, customers may only upgrade to a
    later version of the same release as indicated by the applicable row in
    the Software Versions and Fixes table.

    Cisco TAC contacts are as follows.
     * +1 800 553 2447 (toll-free from within North America)
     * +1 408 526 7209 (toll call from anywhere in the world)
     * e-mail: tac@cisco.com
    See <http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml>
    http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional
    TAC contact information, including special localized telephone numbers and
    instructions and e-mail addresses for use in various languages.

    Please have your product serial number available and give the URL of this
    notice as evidence of your entitlement to a free upgrade. Free upgrades
    for non-contract customers must be requested through the TAC.

    Please do not contact either "psirt@cisco.com" or
    "security-alert@cisco.com" for software upgrades.

    There is no workaround short of disabling the RTR responder. It is
    possible to mitigate the vulnerability by applying the ACL on the router.

    If you want to disable the RTR, you need to execute the following

        Router#conf t
        Enter configuration commands, one per line. End with CNTL/Z.
        Router(config)#no rtr responder
        Router#copy running-config startup-config

    If you want to block all offending packets on your network edge, then you
    should create an ACL, or modify an existing one, to contain an entry

        Router#conf t
        Enter configuration commands, one per line. End with CNTL/Z.
        Router(config)#access-list 101 deny udp any any eq 1967
        Router(config)#interface eth0
        Router(config)#ip access-group 101 in

    In this example the interface eth0 is assumed to be facing toward the
    network edge. You will have to substitute it for the correct interface on
    your router.

    This will prevent any packet that is destined to the port 1967/UDP from
    entering your network. If you need to enable these packets to traverse
    your network, then the ACL must exclude only your internal routers.

    In addition to filtering packets at the network edge, you may apply
    filtering on the device itself and permit packets only from known good
    sources. This will contribute to the overall mitigation of this issue.

        Router#conf t
        Enter configuration commands, one per line. End with CNTL/Z.
        Router(config)#access-list 101 permit udp eq 1967
        Router(config)#access-list 101 deny udp any eq 1967
        Router(config)#interface eth0
        Router(config)#ip access-group 101 in

    In this example, is the legitimate source and is the
    address of the router itself.


    The information has been provided by <mailto:psirt@cisco.com> Cisco
    Systems Product Security Incident Response Team.


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