Cisco IOS XR Software SSHv1 Denial of Service Vulnerability

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Updated:July 10, 2015
Document ID:1454785521703920

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Cisco Security Advisory

Cisco IOS XR Software SSHv1 Denial of Service Vulnerability

Severity
Advisory ID:
cisco-sa-20110525-iosxr-ssh
First Published:
2011 May 25 16:00 GMT
Version 1.0:
Final

Summary

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: http://www.cisco.com/web/about/security/intelligence/ios-ref.html#9.

    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: http://www.cisco.com/en/US/prod/collateral/iosswrel/ps8803/ps5845/product_bulletin_c25-478699.html.

    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 vulnerable.


    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 vulnerability.

Details

  • 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.

Workarounds

  • 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.


Fixed Software

  • 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.

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.

Cisco Security Vulnerability Policy

  • 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.

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Revision History

  • Revision 1.0

    2011-May-25

    Initial public release.
    Show Less

Cisco Security Vulnerability Policy

  • 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.

Subscribe to Cisco Security Notifications