[apops] Cisco Security Advisory: Cisco IOS XR Software SSH Denial of Ser

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  • Subject: [apops] Cisco Security Advisory: Cisco IOS XR Software SSH Denial of Service Vulnerability
  • From: Cisco Systems Product Security Incident Response Team <psirt at cisco dot com>
  • Date: Wed, 20 Jan 2010 11:09:20 -0500
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      Cisco Security Advisory: Cisco IOS XR Software SSH Denial of Service
      Advisory ID: cisco-sa-20100120-xr-ssh
      Revision 1.0
      For Public Release 2010 January 20 1600 UTC (GMT)
      The SSH server implementation in Cisco IOS XR Software contains a
      vulnerability that an unauthenticated, remote user could exploit to
      cause a denial of service condition.
      An attacker could trigger this vulnerability by sending a crafted SSH
      version 2 packet that may cause a new SSH connection handler process to
      crash. Repeated exploitation may cause each new SSH connection handler
      process to crash and lead to a significant amount of memory being
      consumed, which could introduce instability that may adversely impact
      other system functionality. During this event, the parent SSH daemon
      process will continue to function normally.
      Cisco has released free software updates that address this
      This advisory is posted at
      Affected Products
      Vulnerable Products
      This vulnerability affects Cisco IOS XR systems that are running an
      affected version of Cisco IOS XR Software and have the SSH server
      feature enabled. A system with the SSH server feature enabled will
      have the command ssh server [v2] present in its configuration. Refer
      to the "Cisco IOS XR System Security Configuration Guide" at
      for additional details regarding configuration of the SSH server in Cisco
      IOS XR Software.
      The SSH server can only be enabled in Cisco IOS XR Software if
      the "security" Package Information Envelope (PIE) is installed.
      Administrators can issue the show install summary command to confirm
      if the security PIE is installed. This command will display an active
      package similar to "<platform>-k9sec-<version>" or, for example,
      "c12k-k9sec-3.6.1" if the security PIE is installed.
      Refer to the "Software Version and Fixes" section of this advisory for
      information on specific affected software versions.
      Products Confirmed Not Vulnerable
      SSH server implementations in Cisco IOS Software and Cisco IOS XE
      Software are not affected by this vulnerability.
      No other Cisco products are currently known to be affected by this
      Cisco IOS XR Software is a member of the Cisco IOS Software family that
      uses a microkernel-based distributed operating system infrastructure.
      Cisco IOS XR Software runs on the Cisco CRS-1 Carrier Routing System,
      Cisco 12000 Series Routers, and Cisco ASR 9000 Series Aggregation
      Services Routers. More information on Cisco IOS XR Software is available
      at http://www.cisco.com/en/US/products/ps5845/index.html.
      The SSH protocol was developed as a secure replacement for the Telnet,
      FTP, rlogin, remote shell (rsh), and Remote Copy Protocol (RCP)
      protocols, which allow for remote device access. SSH varies from
      these older protocols in that it provides strong authentication and
      confidentiality and uses encrypted transactions.
      The SSH server implementation in Cisco IOS XR Software contains a
      vulnerability that an unauthenticated, remote user could exploit to
      cause a denial of service condition.
      The vulnerability is triggered when a new SSH handler process handles
      a crafted SSH version 2 packet, which may cause the process to crash.
      During this event, a significant amount of memory may be consumed.
      Repeated exploitation may impact other system functionality, depending
      upon the size of the available memory and the duration of attack.
      Although exploitation of this vulnerability does not require user
      authentication, the TCP three-way handshake must be completed, and some
      SSH protocol negotiation must occur.
      The SSH service will continue to function normally during an after an
      During exploitation of this vulnerability, the system may generate the
      following messages:
          RP/0/RP1/CPU0:Jan 14 16:56:34.885 : dumper[59]: %OS-DUMPER-7-DUMP_ATTRIBUTE : Dump request with attribute 407 for process pkg/bin/sshd_child_handler
          RP/0/RP1/CPU0:Jan 14 16:56:34.897 : dumper[59]: %OS-DUMPER-7-SIGSEGV : Thread 1 received SIGSEGV
          RP/0/RP1/CPU0:Jan 14 16:56:34.901 : dumper[59]: %OS-DUMPER-7-BUS_ADRERR : Accessed BadAddr 50199000 at PC 4a280c64
          RP/0/RP1/CPU0:Jan 14 16:56:34.906 : dumper[59]: %OS-DUMPER-4-CRASH_INFO : Crashed pid = 21733716 (pkg/bin/sshd_child_handler)
      This vulnerability is documented in Cisco bug ID CSCsu10574 and has been
      assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2010-0137.
      Vulnerability Scoring Details
      Cisco has provided scores for the vulnerability in this advisory based
      on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in
      this Security Advisory is done in accordance with CVSS version 2.0.
      CVSS is a standards-based scoring method that conveys vulnerability
      severity and helps determine urgency and priority of response.
      Cisco has provided a base and temporal score. Customers can then
      compute environmental scores to assist in determining the impact of the
      vulnerability in individual networks.
      Cisco has provided an FAQ to answer additional questions regarding CVSS
      Cisco has also provided a CVSS calculator to help compute the
      environmental impact for individual networks at:
      * CSCsu10574 ("sshd_child_handler crashes with crafted SSHv2 packet")
      CVSS Base Score - 7.8
          Access Vector -            Network
          Access Complexity -        Low
          Authentication -           None
          Confidentiality Impact -   None
          Integrity Impact -         None
          Availability Impact -      Complete
      CVSS Temporal Score - 6.4
          Exploitability -           Functional
          Remediation Level -        Official-Fix
          Report Confidence -        Confirmed
      Successful exploitation of the vulnerability described in this advisory
      could result in a crash of the SSH connection handler process. Repeated
      exploitation may impact other system functionality, depending upon the
      size of the available memory and the duration of attack.
      Software Versions and Fixes
      When considering software upgrades, also consult
      http://www.cisco.com/go/psirt and any subsequent advisories to determine
      exposure and a complete upgrade solution.
      In all cases, customers should exercise caution to be certain the
      devices to be upgraded contain sufficient memory and that current
      hardware and software configurations will continue to be supported
      properly by the new release. If the information is not clear, contact
      the Cisco Technical Assistance Center (TAC) or your contracted
      maintenance provider for assistance.
      This vulnerability can be addressed by applying the appropriate
      Software Maintenance Upgrade (SMU), per the table below.
      Installation of the appropriate SMU does not require a system
      reload. Refer to the document "Guidelines for Cisco IOS XR Software"
      for additional information on Cisco IOS XR Software and SMUs.
      | Cisco   | SMU Name and SMU ID                                                   |
      |IOS XR   |-----------------------------------------------------------------------|
      | Release | CRS-1                      | XR12000                     | ASR 9000   |
      |         |                            |                             | (*)        |
      |         | hfr-k9sec-3.4.1.CSCsu10574 | c12k-k9sec-3.4.1.CSCsu10574 | Not        |
      | 3.4.1   |                            |                             | applicable |
      |         | AA03509                    | AA03532                     |            |
      |         | hfr-k9sec-3.4.2.CSCsu10574 | c12k-k9sec-3.4.2.CSCsu10574 | Not        |
      | 3.4.2   |                            |                             | applicable |
      |         | AA03510                    | AA03531                     |            |
      |         | hfr-k9sec-3.4.3.CSCsu10574 | c12k-k9sec-3.4.3.CSCsu10574 | Not        |
      | 3.4.3   |                            |                             | applicable |
      |         | AA03511                    | AA03530                     |            |
      |         | hfr-k9sec-3.5.2.CSCsu10574 | c12k-k9sec-3.5.2.CSCsu10574 | Not        |
      | 3.5.2   |                            |                             | applicable |
      |         | AA03512                    | AA03529                     |            |
      |         | hfr-k9sec-3.5.3.CSCsu10574 | c12k-k9sec-3.5.3.CSCsu10574 | Not        |
      | 3.5.3   |                            |                             | applicable |
      |         | AA03513                    | AA03528                     |            |
      |         | hfr-k9sec-3.5.4.CSCsu10574 | c12k-k9sec-3.5.4.CSCsu10574 | Not        |
      | 3.5.4   |                            |                             | applicable |
      |         | AA03514                    | AA03527                     |            |
      |         | hfr-k9sec-3.6.0.CSCsu10574 | c12k-k9sec-3.6.0.CSCsu10574 | Not        |
      | 3.6.0   |                            |                             | applicable |
      |         | AA03515                    | AA03526                     |            |
      |         | hfr-k9sec-3.6.1.CSCsu10574 | c12k-k9sec-3.6.1.CSCsu10574 | Not        |
      | 3.6.1   |                            |                             | applicable |
      |         | AA03516                    | AA03525                     |            |
      | 3.6.2   | Not affected               | Not affected                | Not        |
      |         |                            |                             | applicable |
      | 3.6.3   | Not affected               | Not affected                | Not        |
      |         |                            |                             | applicable |
      |         | hfr-k9sec-3.7.0.CSCsu10574 | c12k-k9sec-3.7.0.CSCsu10574 | Not        |
      | 3.7.0   |                            |                             | applicable |
      |         | AA03519                    | AA03522                     |            |
      | 3.7.1   | Not affected               | Not affected                | Not        |
      |         |                            |                             | affected   |
      | 3.7.2   | Not affected               | Not affected                | Not        |
      |         |                            |                             | affected   |
      | 3.8.x   | Not affected               | Not affected                | Not        |
      |         |                            |                             | applicable |
      | 3.9.x   | Not affected               | Not affected                | Not        |
      |         |                            |                             | affected   |
      (*) Not all Cisco IOS XR Software versions are supported by the Cisco
      ASR 9000 Aggregation Services Routers.
      There are no workarounds for this vulnerability. Network administrators
      are advised to apply mitigation techniques to help limit exposure to the
      vulnerability. Mitigation techniques consist of allowing only legitimate
      devices to connect to the routers.
      These access restrictions can be accomplished by using interface
      access control lists (ACLs) or the Management Plane Protection (MPP)
      feature that is available in Cisco IOS XR Software Release 3.5 and
      later. For information on MPP, refer to the configuration guide
      and the MPP command reference at
      Infrastructure ACLs (iACLs) are also a useful technique to mitigate
      potential exploitation of this vulnerability.
      For more information on these mitigations, consult the Cisco
      Guide to Harden Cisco IOS XR Devices, which is available at
      Note that access classes in line templates applied to VTY pools are not
      an effective mitigation for this vulnerability.
      Obtaining Fixed Software
      Cisco has released free software updates that address this
      vulnerability. Prior to deploying software, customers should consult
      their maintenance provider or check the software for feature set
      compatibility and known issues specific to their environment.
      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
      or as otherwise set forth at Cisco.com Downloads at
      Do not contact psirt at cisco dot com or security-alert at cisco dot com for software
      Customers with Service Contracts
      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.
      Customers using Third Party Support Organizations
      Customers whose Cisco products are provided or maintained through prior
      or existing agreements with third-party support organizations, such
      as Cisco Partners, authorized resellers, or service providers should
      contact that support organization for guidance and assistance with the
      appropriate course of action in regards to this advisory.
      The effectiveness of any workaround or fix is dependent on specific
      customer situations, such as product mix, network topology, traffic
      behavior, and organizational mission. Due to the variety of affected
      products and releases, customers should consult with their service
      provider or support organization to ensure any applied workaround or fix
      is the most appropriate for use in the intended network before it is
      Customers without Service Contracts
      Customers who purchase direct from Cisco but do not hold a Cisco service
      contract, and customers who purchase through third-party vendors but are
      unsuccessful in obtaining fixed software through their point of sale
      should acquire upgrades by contacting the Cisco Technical Assistance
      Center (TAC). 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 at cisco dot com
      Customers should have their product serial number available and be
      prepared to give the URL of this notice as evidence of entitlement to a
      free upgrade. Free upgrades for non-contract customers must be requested
      through the TAC.
      Refer to http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html
      for additional TAC contact information, including localized telephone numbers,
      and instructions and e-mail addresses for use in various languages.
      Exploitation and Public Announcements
      The Cisco PSIRT is not aware of any public announcements or malicious
      use of the vulnerability described in this advisory.
      This vulnerability was discovered by Cisco during internal testing.
      Status of this Notice: FINAL
      A stand-alone copy or Paraphrase of the text of this document that omits
      the distribution URL in the following section is an uncontrolled copy,
      and may lack important information or contain factual errors.
      This advisory is posted on Cisco's worldwide website at:
      In addition to worldwide web posting, a text version of this notice is
      clear-signed with the Cisco PSIRT PGP key and is posted to the following
      e-mail and Usenet news recipients.
        * cust-security-announce at cisco dot com
        * first-bulletins at lists dot first dot org
        * bugtraq at securityfocus dot com
        * vulnwatch at vulnwatch dot org
        * cisco at spot dot colorado dot edu
        * cisco-nsp at puck dot nether dot net
        * full-disclosure at lists.grok dot org dot uk
        * comp.dcom.sys.cisco at newsgate dot cisco dot com
      Future updates of this advisory, if any, will be placed on Cisco's
      worldwide website, but may or may not be actively announced on mailing
      lists or newsgroups. Users concerned about this problem are encouraged
      to check the above URL for any updates.
      Revision History
      | Revision 1.0  | 2010-January-20  | Initial public release  |
      Cisco Security Procedures
      Complete information on reporting security vulnerabilities
      in Cisco products, obtaining assistance with security
      incidents, and registering to receive security information
      from Cisco, is available on Cisco's worldwide website at
      This includes instructions for press inquiries regarding
      Cisco security notices. All Cisco security advisories are available at
      Copyright 2008-2010 Cisco Systems, Inc. All rights reserved.
      Updated: Jan 20, 2010                             Document ID: 111459
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