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             AUSCERT External Security Bulletin Redistribution

         Cisco IOS XR Software Intermediate System-to-Intermediate
                  System Denial of Service Vulnerability
                             21 February 2020


        AusCERT Security Bulletin Summary

Product:           Cisco IOS XR Software
Publisher:         Cisco Systems
Operating System:  Network Appliance
Impact/Access:     Denial of Service -- Existing Account
Resolution:        Patch/Upgrade
CVE Names:         CVE-2019-16027  

Reference:         ESB-2020.0421

Original Bulletin: 

- --------------------------BEGIN INCLUDED TEXT--------------------

Cisco IOS XR Software Intermediate System-to-Intermediate System Denial of
Service Vulnerability

Priority:        High

Advisory ID:     cisco-sa-20200122-ios-xr-dos

First Published: 2020 January 22 16:00 GMT

Last Updated:    2020 February 19 18:42 GMT

Version 1.2:     Final

Workarounds:     No workarounds availableCisco Bug IDs:   CSCvr62342



CVSS Score:


  o A vulnerability in the implementation of the Intermediate
    System-to-Intermediate System (IS-IS) routing protocol functionality in
    Cisco IOS XR Software could allow an authenticated, remote attacker to
    cause a denial of service (DoS) condition in the IS-IS process.

    The vulnerability is due to improper handling of a Simple Network
    Management Protocol (SNMP) request for specific Object Identifiers (OIDs)
    by the IS-IS process. An attacker could exploit this vulnerability by
    sending a crafted SNMP request to the affected device. A successful exploit
    could allow the attacker to cause a DoS condition in the IS-IS process.

    Cisco has released software updates that address this vulnerability. There
    are no workarounds that address this vulnerability.

    This advisory is available at the following link:

Affected Products

  o Vulnerable Products

    This vulnerability affects Cisco devices if they are running Cisco IOS XR
    Software releases earlier than 6.6.3, 7.0.2, 7.1.1, or 7.2.1 and they
    configured with both the IS-IS routing protocol and SNMP versions 1, 2c, or

    Cisco has confirmed that this vulnerability affects both Cisco IOS XR
    32-bit Software and Cisco IOS XR 64-bit Software.

    Determine Whether the Device Has a Vulnerable Configuration

    To determine if the device is configured for IS-IS routing, administrators
    can use the show running-config router isis EXEC command in the CLI. If the
    device is configured for IS-IS routing, this command will return output.
    The following example shows the partial output of the show running-config
    router isis command on a device that is configured for IS-IS routing.

        #show running-config router isis
        router isis {isp}
        is-type level-2-only

    To determine if the device is configured for SNMP, administrators can use
    the show running-config snmp EXEC command in the CLI. If the device is
    configured for SNMP, this command will return output. The following
    examples show the partial output of the show running-config snmp command on
    a device that is configured for SNMP. Only one version of SNMP needs to be
    configured for the device to be vulnerable. The vulnerability is triggered
    through an SNMP query, but the configuration can be for read or write.


        #show running-config snmp
        snmp-server community {public ro}


        #show running-config snmp
        snmp-server group {SNMP_GROUP1} v2c


        #show running-config snmp
        snmp-server view {SNMP_VIEW1 included}
        snmp-server group {SNMP_GROUP1} v3 {auth read SNMP_VIEW1}

    Products Confirmed Not Vulnerable

    Only products listed in the Vulnerable Products section of this advisory
    are known to be affected by this vulnerability.

    Cisco has confirmed that this vulnerability does not affect the following
    Cisco products:

       Cisco IOS and IOS XE Software
       Cisco IOS XR7-LNT Software
       Cisco NX-OS Software


  o There are no workarounds that address this vulnerability. However,
    administrators may choose to perform one of the following mitigations:

    Disable SNMP: This vulnerability is exploited by doing an SNMP query of a
    special MIB OID range. If SNMP is disabled, this vulnerability cannot be
    exploited. For mitigation of this vulnerability if SNMP is enabled on the
    device, contact Cisco TAC for assistance with the OIDs.

    Configure an access control list: Administrators can also configure an
    access control list (ACL) on an SNMP community to filter incoming SNMP
    requests to ensure that SNMP queries are performed only by trusted SNMP
    clients. For information about configuring ACLs, see the Cisco Guide to
    Harden Cisco IOS XR Devices .

Fixed Software

  o Cisco has released free software updates that address the vulnerability
    described in this advisory. Customers may only install and expect support
    for software versions and feature sets for which they have purchased a
    license. By installing, downloading, accessing, or otherwise using such
    software upgrades, customers agree to follow the terms of the Cisco
    software license:

    Additionally, customers may only download software for which they have a
    valid license, procured from Cisco directly, or through a Cisco authorized
    reseller or partner. In most cases this will be a maintenance upgrade to
    software that was previously purchased. Free security software updates do
    not entitle customers to a new software license, additional software
    feature sets, or major revision upgrades.

    When considering software upgrades , customers are advised to regularly
    consult the advisories for Cisco products, which are available from the
    Cisco Security Advisories and Alerts page , to determine exposure and a
    complete upgrade solution.

    In all cases, customers should ensure that the devices to be upgraded
    contain sufficient memory and confirm that current hardware and software
    configurations will continue to be supported properly by the new release.
    If the information is not clear, customers are advised to contact the Cisco
    Technical Assistance Center (TAC) or their contracted maintenance

    Customers Without Service Contracts

    Customers who purchase directly from Cisco but do not hold a Cisco service
    contract and customers who make purchases through third-party vendors but
    are unsuccessful in obtaining fixed software through their point of sale
    should obtain upgrades by contacting the Cisco TAC:

    Customers should have the product serial number available and be prepared
    to provide the URL of this advisory as evidence of entitlement to a free

    Fixed Releases

    Cisco fixed this vulnerability in Cisco IOS XR Software Release 6.6.3.
    Cisco also plans to fix this vulnerability in Cisco IOS XR Software
    releases 7.0.2, 7.1.1, and 7.2.1.

    Customers are advised to install the appropriate SMU as shown in the
    following table. Customers who require SMUs for other platforms and
    releases are advised to contact their support organization.

    IOS XR Release        Platform      SMU Name
    4.3.2                 XR12000       c12k-4.3.2.CSCvr62342
    5.2.5                 NCS6K         ncs6k-5.2.5.CSCvr62342
    6.1.2                 ASR9K-PX      asr9k-px-6.1.2.CSCvr62342
    6.1.3                 ASR9K-PX      asr9k-px-6.1.3.CSCvr62342
    6.1.3                 NCS5K         ncs5k-6.1.3.CSCvr62342
    6.1.3                 NCS5500       ncs5500-6.1.3.CSCvr62342
    6.1.4                 ASR9K-PX      asr9k-px-6.1.4.CSCvr6234
    6.1.4                 CRS-PX        hfr-px-6.1.4.CSCvr62342
    6.1.4                 NCS5500       ncs5500-6.1.4.CSCvr62342
    6.1.4                 NCS5K         ncs5k-6.1.4.CSCvr62342
    6.1.4                 XRV9K         xrv9k-6.1.4.CSCvr62342
    6.2.2                 ASR9K-PX      asr9k-px-6.2.2.CSCvr62342
    6.2.2                 NCS6K         ncs6k-6.2.2.CSCvr62342
    6.2.25                NCS5K         ncs5k-6.2.25.CSCvr62342
    6.2.25                NCS6K         ncs6k-6.2.25.CSCvr62342
    6.2.3                 NCS5K         ncs5k-6.2.3.CSCvr62342
    6.2.3                 ASR9K-PX      asr9k-px-6.2.3.CSCvr62342
    6.2.3                 ASR9K-X64     asr9k-x64-6.2.3.CSCvr62342
    6.2.3                 CRS-PX        hfr-px-6.2.3.CSCvr62342
    6.2.3                 NCS5500       ncs5500-6.2.3.CSCvr62342
    6.2.3                 XRV9K         xrv9k-6.2.3.CSCvr62342
    6.2.3                 NCS6K         ncs6k-6.2.3.CSCvr62342
    6.3.15                NCS5500       ncs5500-6.3.15.CSCvr62342
    6.3.2                 ASR9K-PX      asr9k-px-6.3.2.CSCvr62342
    6.3.2                 ASR9K-X64     asr9k-x64-6.3.2.CSCvr62342
    6.3.3                 ASR9K-X64     asr9k-x64-6.3.3.CSCvr62342
    6.3.3                 ASR9K-PX      asr9k-px-6.3.3.CSCvr62342
    6.3.3                 NCS5K         ncs5k-6.3.3.CSCvr62342
    6.3.3                 NCS540        ncs540-6.3.3.CSCvr62342
    6.3.3                 NCS5500       ncs5500-6.3.3.CSCvr62342
    6.3.3                 NCS6K         ncs6k-6.3.3.CSCvr62342
    6.4.2                 ASR9K-PX      asr9k-px-6.4.2.CSCvr62342
    6.4.2                 ASR9K-X64     asr9k-x64-6.4.2.CSCvr62342
    6.4.2                 CRS-PX        hfr-px-6.4.2.CSCvr62342
    6.4.2                 NCS5K         ncs5k-6.4.2.CSCvr62342
    6.4.2                 NCS6K         ncs6k-6.4.2.CSCvr62342
    6.4.2                 XRV9K         xrv9k-6.4.2.CSCvr62342
    6.5.2                 ASR9K-PX      asr9k-px-6.5.2.CSCvr62342
    6.5.2                 ASR9K-X64     asr9k-x64-6.5.2.CSCvr62342
    6.5.2                 NCS5K         ncs5k-6.5.2.CSCvr62342
    6.5.2                 NCS5500       ncs5500-6.5.2.CSCvr62342
    6.5.3                 ASR9K-X64     asr9k-x64-6.5.3.CSCvr62342
    6.5.3                 NCS5500       ncs5500-6.5.3.CSCvr62342
    6.5.3                 NCS540        ncs540-6.5.3.CSCvr62342
    6.5.3                 NCS5K         ncs5k-6.5.3.CSCvr62342
    6.5.3                 ASR9K-PX      asr9k-px-6.5.3.CSCvr62342
    6.5.3                 XRV9K         xrv9k-6.5.3.CSCvr62342
    6.6.1                 NCS5500       ncs5500-6.6.1.CSCvr62342
    6.6.2                 ASR9K-PX      asr9k-px-6.6.2.CSCvr62342
    6.6.2                 ASR9K-X64     asr9k-x64-6.6.2.CSCvr62342
    6.6.2                 XRV9K         xrv9k-6.6.2.CSCvr62342
    6.6.25                NCS5500       ncs5500-6.6.25.CSCvr62342
    6.6.25                NCS540        ncs540-6.6.25.CSCvr62342
    6.6.25                NCS560        ncs560-6.6.25.CSCvr62342

    To download the SMUs from the Software Center on Cisco.com , do the

     1. Click Browse All .
     2. Choose IOS and NX-OS Software > IOS XR > IOS XR Software > Optical
        Networking or Routers .
     3. Choose a specific product and model from the right pane of the product
     4. Choose a release from the left pane of the product page.

Exploitation and Public Announcements

  o The Cisco Product Security Incident Response Team (PSIRT) is not aware of
    any public announcements or malicious use of the vulnerability that is
    described in this advisory.


  o This vulnerability was found during the resolution of a Cisco TAC support

Cisco Security Vulnerability Policy

  o To learn about Cisco security vulnerability disclosure policies and
    publications, see the Security Vulnerability Policy . This document also
    contains instructions for obtaining fixed software and receiving security
    vulnerability information from Cisco.

Action Links for This Advisory

  o Snort Rule 52645
    Snort Rule 52646
    Snort Rule 52647
    Snort Rule 52648
    Snort Rule 52649


  o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/

Revision History

  o +---------+---------------------+-------------+--------+------------------+
    | Version |     Description     |   Section   | Status |       Date       |
    |         | Updated Fixed       | Fixed       |        |                  |
    | 1.2     | Releases table to   | Releases    | Final  | 2020-February-19 |
    |         | add current SMUs.   |             |        |                  |
    |         | Changed en dashes   | Title,      |        |                  |
    |         | to hyphens          | Summary,    |        |                  |
    | 1.1     | throughout. No      | and         | Final  | 2020-February-04 |
    |         | content changes     | Vulnerable  |        |                  |
    |         | were made.          | Products.   |        |                  |
    | 1.0     | Initial public      | -           | Final  | 2020-January-22  |
    |         | release.            |             |        |                  |

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