Summary

• A vulnerability in the Secure Shell (SSH) session management for Cisco Wireless LAN Controller (WLC) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.

  The vulnerability exists because the SSH process is not properly deleted when an SSH connection to the device is disconnected. An attacker could exploit this vulnerability by repeatedly opening SSH connections to an affected device. A successful exploit could allow the attacker to exhaust system resources by initiating multiple SSH connections to the device that are not effectively terminated, which could result in a DoS condition.

  Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20191016-wlc-ssh-dos

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco WLC Software releases 8.5.140.0 and earlier.

  Products Confirmed Not Vulnerable

  Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.

Indicators of Compromise

• Exploitation of this vulnerability could cause high system memory usage. It could also cause a high number of SSH connections.

  Customers can monitor current system memory usage by using the show memory statistics command. The following example shows the memory use information that is available in the output of this command:

  (Cisco Controller) > show memory statistics
  
   System Memory Statistics:
  
  Total System Memory............: 724688896 bytes (691.16 MB)
  Used System Memory.............: 284012544 bytes (270.87 MB)
  Free System Memory.............: 440676352 bytes (420.29 MB)
  Effective Free Memory..........: 289517568 bytes (276.12 MB)
  Bytes allocated from RTOS......: 12292096 bytes (11.72 MB)
  Chunks Free....................: 7 bytes
  Number of mmapped regions......: 83
  Total space in mmapped regions.: 159522816 bytes (152.14 MB)
  Total allocated space..........: 12042392 bytes (11.48 MB)
  Total non-inuse space..........: 249704 bytes (243.85 KB)
  Top-most releasable space......: 214616 bytes (209.58 KB)
  Total allocated (incl mmap)....: 171814912 bytes (163.86 MB)
  Total used (incl mmap).........: 171565208 bytes (163.62 MB)
  
  

  Customers can monitor current SSH connections by using the show login-session command. The following example shows the SSH connection information that is available in the output of this command:

  (Cisco Controller) > show login-session
  
  ID    User Name    Connection From   Idle Time   Session Time
  -- --------------- --------------- ------------ ------------
  00     admin             SSH           00:00:00      00:19:04
  
  .
  
  .
  
  .
  

Workarounds

• There are no workarounds that address this vulnerability.

Fixed Software

• Cisco has released free software updates that address the vulnerability described in this advisory. Customers may only install and expect support for software versions and feature sets for which they have purchased a license. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license:
  https://www.cisco.com/c/en/us/products/end-user-license-agreement.html

  Additionally, customers may only download software for which they have a valid license, procured from Cisco directly, or through a Cisco authorized reseller or partner. In most cases this will be a maintenance upgrade to software that was previously purchased. Free security software updates do not entitle customers to a new software license, additional software feature sets, or major revision upgrades.

  When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories and Alerts page, 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.

  Customers Without Service Contracts

  Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco TAC:
  https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html

  Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade.

  Fixed Releases

  Customers are advised to upgrade to an appropriate release as indicated in the table in this section. To help ensure a complete upgrade solution, consider that this advisory is part of a collection that includes the following advisories:

  • cisco-sa-20191016-airo-capwap-dos: Cisco Aironet Access Points and Catalyst 9100 Access Points CAPWAP Denial of Service Vulnerability
  • cisco-sa-20191016-airo-pptp-dos: Cisco Aironet Access Points Point-to-Point Tunneling Protocol Denial of Service Vulnerability
  • cisco-sa-20191016-airo-unauth-access: Cisco Aironet Access Points Unauthorized Access Vulnerability
  • cisco-sa-20191016-wlc-ssh-dos: Cisco Wireless LAN Controller Secure Shell Denial of Service Vulnerability

  In the following table, the left column lists Cisco software releases. The center column indicates whether a release is affected by the vulnerability described in this advisory and the first release that includes the fix for this vulnerability. The right column indicates whether a release is affected by all the vulnerabilities described in this collection of advisories and which release includes fixes for those vulnerabilities.

  Cisco WLC Software Major Release	First Fixed Release for This Vulnerability	Recommended Release for All Vulnerabilities Described in the Collection of Advisories
  Earlier than 8.0	8.5.151.0	8.5.151.0
  8.0	8.5.151.0	8.5.151.0
  8.1	8.5.151.0	8.5.151.0
  8.2	8.5.151.0	8.5.151.0
  8.3	8.5.151.0	8.5.151.0
  8.4	8.5.151.0	8.5.151.0
  8.5	8.5.151.0	8.5.151.0
  8.6	Not vulnerable	8.8.125.0
  8.7	Not vulnerable	8.8.125.0
  8.8	Not vulnerable	8.8.125.0
  8.9	Not vulnerable	8.9.111.0
  8.10	Not vulnerable	Not vulnerable

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.

Source

• This vulnerability was found during the resolution of a Cisco TAC support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20191016-wlc-ssh-dos

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2019-October-16

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