Cisco IOS XR Software SSHv1 Denial of Service Vulnerability

Summary

• 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 filesystem.

  Cisco has released software updates that address this vulnerability.

  This advisory is posted at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20110525-iosxr-ssh.

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.