[apops] Cisco Security Advisory: Cisco IOS XR Software SSHv1 Denial of S

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  • Subject: [apops] Cisco Security Advisory: Cisco IOS XR Software SSHv1 Denial of Service Vulnerability
  • From: Cisco Systems Product Security Incident Response Team <psirt at cisco dot com>
  • Date: Wed, 25 May 2011 12:16:42 -0400
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      Cisco Security Advisory: Cisco IOS XR Software SSHv1 Denial of Service Vulnerability
      Advisory ID: cisco-sa-20110525-iosxr-ssh
      Revision 1.0
      For Public Release 2011 May 25 1600 UTC (GMT)
      Cisco IOS XR Software contains a vulnerability in the SSH application
      that may result in a denial of service condition when the SSH version
      1 (SSHv1) protocol is used. The vulnerability is a result of
      unremoved sshd_lock files consuming all available space in the /tmp
      Cisco has released free software updates that address this
      This advisory is posted at:
      Affected Products
      This vulnerability affects all unfixed versions of Cisco IOS XR
      Software devices configured to accept SSHv1 connections. Details on
      the affected versions can be found in the Software Versions and Fixes
      section of this advisory.
      Vulnerable Products
      To determine the Cisco IOS XR Software release that is running on a
      Cisco product, administrators can log in to the device and issue the 
      show version command to display the system banner. The system banner
      confirms that the device is running Cisco IOS XR Software by
      displaying text similar to "Cisco IOS XR Software". The software
      version is displayed after the text "Cisco IOS XR Software".
      The following example identifies a Cisco CRS-1 that is running Cisco
      IOS XR Software Release 3.6.2:
          RP/0/RP0/CPU0:CRS#show version
          Tue Aug 18 14:25:17.407 AEST
          Cisco IOS XR Software, Version 3.6.2[00]
          Copyright (c) 2008 by Cisco Systems, Inc.
          ROM: System Bootstrap, Version 1.49(20080319:195807) [CRS-1 ROMMON],
          CRS uptime is 4 weeks, 4 days, 1 minute
          System image file is "disk0:hfr-os-mbi-3.6.2/mbihfr-rp.vm"
          cisco CRS-8/S (7457) processor with 4194304K bytes of memory.
          7457 processor at 1197Mhz, Revision 1.2
          17 Packet over SONET/SDH network interface(s)
          1 DWDM controller(s)
          17 SONET/SDH Port controller(s)
          8 TenGigabitEthernet/IEEE 802.3 interface(s)
          2 Ethernet/IEEE 802.3 interface(s)
          1019k bytes of non-volatile configuration memory.
          38079M bytes of hard disk.
          981440k bytes of ATA PCMCIA card at disk 0 (Sector size 512 bytes).
          Configuration register on node 0/0/CPU0 is 0x102
          Boot device on node 0/0/CPU0 is mem:
          !--- output truncated
      The following example identifies a Cisco 12404 router that is running
      Cisco IOS XR Software Release 3.7.1:
          RP/0/0/CPU0:GSR#show version
          Cisco IOS XR Software, Version 3.7.1[00]
          Copyright (c) 2008 by Cisco Systems, Inc.
          ROM: System Bootstrap, Version 12.0(20051020:160303) SOFTWARE
          Copyright (c) 1994-2005 by cisco Systems,  Inc.
          GSR uptime is 3 weeks, 6 days, 3 hours, 20 minutes
          System image file is "disk0:c12k-os-mbi-3.7.1/mbiprp-rp.vm"
          cisco 12404/PRP (7457) processor with 2097152K bytes of memory.
          7457 processor at 1266Mhz, Revision 1.2
          1 Cisco 12000 Series Performance Route Processor
          1 Cisco 12000 Series - Multi-Service Blade Controller
          1 1 Port ISE Packet Over SONET OC-48c/STM-16 Controller (1 POS)
          1 Cisco 12000 Series SPA Interface Processor-601/501/401
          3 Ethernet/IEEE 802.3 interface(s)
          1 SONET/SDH Port controller(s)
          1 Packet over SONET/SDH network interface(s)
          4 PLIM QoS controller(s)
          8 FastEthernet/IEEE 802.3 interface(s)
          1016k bytes of non-volatile configuration memory.
          1000496k bytes of disk0: (Sector size 512 bytes).
          65536k bytes of Flash internal SIMM (Sector size 256k).
          Configuration register on node 0/0/CPU0 is 0x2102
          Boot device on node 0/0/CPU0 is disk0:
          !--- output truncated
      Additional information about Cisco IOS XR Software release naming
      conventions is available in "White Paper: Cisco IOS Reference Guide"
      at the following link: 
      Additional information about Cisco IOS XR Software time-based release
      model is available in "White Paper: Guidelines for Cisco IOS XR
      Software" at the following link: 
      SSHv1 is configured in Cisco IOS XR Software with the configuration
      command ssh server enable. The device is vulnerable if it is running
      an affected Cisco IOS XR Software release and has SSHv1 enabled.
      The following example shows a device that is running Cisco IOS XR
      Software that is configured with SSHv1:
          (Router)# show running-config | inc ssh
          ssh server vrf default
      If the command returns "ssh server v2", then the SSH server is not
      configured to accept SSHv1 connections and the device is not
      Products Confirmed Not Vulnerable
      The following Cisco products are confirmed not vulnerable:
        * Cisco IOS Software
        * Cisco IOS XR Software without SSH enabled
        * Cisco IOS XR Software configured to accept only SSHv2 connections
      No other Cisco products are currently known to be affected by this
      This vulnerability affects Cisco IOS XR devices that are running
      affected software releases and are configured to accept SSHv1
      connections. When an SSHv1 connection is made to the SSH server that
      is running on a Cisco IOS XR device, a file is created in the /tmp
      directory. This file begins with the text "sshd_lock" and may not be
      properly removed when the session ends. Multiple connections may
      consume all available space in the /tmp filesystem and cause the
      system to crash, leading to a denial of service condition.
      This vulnerability is documented in Cisco Bug ID CSCtd64417 ( 
      registered customers only) and has been assigned Common
      Vulnerabilities and Exposures (CVE) ID CVE-2011-0949.
      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 at:
      Cisco has also provided a CVSS calculator to help compute the
      environmental impact for individual networks at
      * SSHv1 may leave /tmp/sshd_lock files
      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 this vulnerability may cause the Cisco IOS
      XR device to crash, resulting in a denial of service condition.
      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 bug was introduced in Cisco IOS XR Software release 3.6.2 and is
      fixed with SMU hfr-k9sec-3.6.2.CSCtd74795. The SMU ID for this fix in
      3.6.2 is AA03656. This vulnerability has been fixed in 3.8.3, 3.9.1,
      and 4.0.0 for customers running later software versions. Software
      version 3.7 is not affected by this vulnerability.
      SSHv1 can be disabled by configuring the SSH server to only accept
      SSHv2 connections. In order to configure a device to only accept
      SSHv2 connections, administrators can issue the command ssh server v2
      Administrators should manually remove lock files after disabling
      SSHv1 or after the server is upgraded to a non-vulnerable version.
      The command run rm /tmp/sshd_lock* will delete any sshd_lock files on
      the system.
      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 upgrades.
      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 deployed.
      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:
      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.
      Customers encountering device crashes during normal network
      operations reported this vulnerability to Cisco.
      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 |             | Initial      |
      | 1.0      | 2011-May-25 | 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 2010-2011 Cisco Systems, Inc. All rights reserved.
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