Cisco ASR 5000 and ASR 5500 TACACS Denial of Service Vulnerability

Summary

• A vulnerability in the TACACS protocol implementation of the Cisco Aggregation Services Router (ASR) 5000 and ASR 5500 (ASR5K) System Software could allow an unauthenticated, remote attacker to cause a partial denial of service (DoS) condition because the vpnmgr process restarts.
  
  The vulnerability is due to improper input validation of the TACACS packet header. An attacker could exploit this vulnerability by sending a crafted TACACS packet to the device. An exploit could allow the attacker to cause a partial DoS condition because the vpnmgr process could restart when parsing the crafted TACACS packet.
  
  Cisco has released software updates that address this vulnerability. Workarounds that mitigate this vulnerability are not available. This advisory is available at the following link:
  http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20151012-asr

Affected Products

• Vulnerable Products

  Cisco ASR 5000 and Cisco ASR 5500 devices running Cisco ASR 5000 Series System Software releases 18.0.0.57828 and 19.0.M0.61045 are vulnerable.

  Products Confirmed Not Vulnerable

  No other Cisco products are currently known to be affected by this vulnerability.

Indicators of Compromise

• The ASR5K will write a core file for the vpnmgr process. This can be viewed using the show crash command-line interface command:
  

  # show crash <#>
  === ==================== ======== ========== =============== =======================
  # Time Process Card/CPU/ SW HW_SER_NUM
  PID VERSION MIO / Crash Card
  === ==================== ======== ========== =============== =======================
  1 2010-Feb-16+07:56:37 vpnmgr 05/0/15340 19.0.M0.61045 #######################
  

Workarounds

• No workarounds are available.

Fixed Software

• When considering software upgrades, customers are advised to consult the Cisco Security Advisories and Responses archive at http://www.cisco.com/go/psirt and review subsequent advisories 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 providers.

Exploitation and Public Announcements

• 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.

URL

• http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20151012-asr

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2015-October-12

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