Summary

• A Cisco IOS device may crash while processing an SSL packet. This can happen during the termination of an SSL-based session. The offending packet is not malformed and is normally received as part of the packet exchange.

  Cisco has released software updates that address this vulnerability. Aside from disabling affected services, there are no available workarounds to mitigate an exploit of this vulnerability.

  This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-ssl.

  Note: The September 24, 2008 IOS Advisory bundled publication includes twelve Security Advisories. Eleven of the advisories address vulnerabilities in Cisco's IOS software, and one advisory addresses vulnerabilities in Cisco Unified Communications Manager. Each Advisory lists the releases that correct the vulnerability described in the Advisory.

  Individual publication links are listed below:

  • https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-iosips
    
  • https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-sip
    
  • https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-cucm
    
  • https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-vpn
    
  • https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-mfi
    
  • https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-ipc
    
  • https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-ubr
    
  • https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-multicast
    
  • https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-sccp
    
  • https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-iosfw
    
  • https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-l2tp
    

Affected Products

• Vulnerable Products

  Devices running Cisco IOS and using SSL-based services are susceptible to this vulnerability. Some of the services that utilize SSL are:

  • HTTP server supporting SSL encryption (HTTPS)
    The following example shows a device that has the standard Cisco IOS HTTP server disabled, but the SSL-enabled Cisco IOS HTTP server enabled:
    

    Router#show running-config | include ip http
    no ip http server
    ip http secure-server
    Router#

  • SSL Virtual Private Network (SSL VPN) also known as AnyConnect VPN
    The following example shows a device that has the SSL VPN feature enabled:
    

    Router#show running-config | include webvpn
    webvpn enable
    webvpn
    Router#

  • Open Settlement Protocol (OSP) for Packet Telephony feature
    The following example shows a device that has the OSP feature enabled and uses HTTPS protocol that is vulnerable:
    

    Router#show running-config | include url
    url https://<host_ip_address>:443/
    Router#

  The Cisco IOS Bug Toolkit may not accurately reflect the affected releases for this advisory. The affected releases are as follows:

  • 12.4(16)MR, 12.4(16)MR1, 12.4(16)MR2
    
  • 12.4(17)
    

  To determine the version of the Cisco IOS software running on a Cisco product, log in to the device and issue the show version command to display the system banner. Cisco IOS Software will identify itself as "Internetwork Operating System Software" or simply "IOS." On the next line of output, the image name will be displayed between parentheses, followed by "Version" and the IOS release name. Other Cisco devices will not have the show version command or will give different output.

  Router#show version
  Cisco IOS Software, 1841 Software (C1841-ADVSECURITYK9-M), Version 12.4(15)T2, 
     RELEASE SOFTWARE (fc7) 
  Technical Support: http://www.cisco.com/techsupport 
  Copyright (c) 1986-2008 by Cisco Systems, Inc. 
  Compiled Thu 17-Jan-08 23:12 by prod_rel_team

  Additional information about Cisco IOS software release naming is available at the following link: http://www.cisco.com/warp/public/620/1.html.

  Products Confirmed Not Vulnerable

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

Details

• This vulnerability is triggered during the termination of an SSL session. Possession of valid credentials such as a username, password or a certificate is not required. SSL protocol uses TCP as a transport protocol. The requirement of the complete TCP 3-way handshake reduces the probability that this vulnerability will be exploited through the use of spoofed IP addresses.

  A device running vulnerable Cisco IOS Software with SSL-based service configured will crash while terminating an SSL session.

  This vulnerability is documented in Cisco Bug ID CSCsj85065 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2008-3798.

Workarounds

• To prevent an exploit of a vulnerable device, SSL-based services need to be disabled. However, if regular maintenance and operation of the device relies on this service, there is no workaround.

  The following command will disable the vulnerable HTTPS service:

  Router(config)#no ip http secure-server
  

  The following command will disable the vulnerable SSL VPN service:

  Router(config)#no webvpn enable
  

  The following command will disable the vulnerable OSP service:

  Router(config)#no settlement <n>
  

  Another option is to revert to HTTP protocol instead using HTTPS. The downside of this workaround is that the settlement information will be sent over the network unprotected.

  It is possible to mitigate this vulnerability by preventing unauthorized hosts from accessing affected devices.

  Control Plane Policing (CoPP)

  Cisco IOS software versions that support Control Plane Policing (CoPP) can be configured to help protect the device from attacks that target the management and control planes. CoPP is available in Cisco IOS release trains 12.0S, 12.2SX, 12.2S, 12.3T, 12.4, and 12.4T.

  In the following CoPP example, the ACL entries that match the exploit packets with the permit action will be discarded by the policy-map drop function, whereas packets that match a deny action (not shown) are not affected by the policy-map drop function:

  
  !-- Include deny statements up front for any protocols/ports/IP addresses that 
  !-- should not be impacted by CoPP
  !-- Include permit statements for the protocols/ports that will be 
  !-- governed by CoPPaccess-list 100 permit tcp any any eq 443
  !-- Permit (Police or Drop)/Deny (Allow) all other Layer3 and Layer4
  !-- traffic in accordance with existing security policies and
  !-- configurations for traffic that is authorized to be sent
  !-- to infrastructure devices.
  !
  !-- Create a Class-Map for traffic to be policed by
  !-- the CoPP feature.
  !
  
  class-map match-all drop-SSL-class match access-group 100
  
  !
  !-- Create a Policy-Map that will be applied to the
  !-- Control-Plane of the device.
  !
  
  policy-map drop-SSL-policy class drop-SSL-class   drop   
  
  !-- Apply the Policy-Map to the Control-Plane of the
  !-- device.
  !
  
  control-plane service-policy input drop-SSL-policy

  Note: In the preceding CoPP example, the ACL entries with the permit action that match the exploit packets will result in the discarding of those packets by the policy-map drop function, whereas packets that match the deny action are not affected by the policy-map drop function.

  Additional information on the configuration and use of the CoPP feature is available at the following links: http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6586/ps6642/prod_white_paper0900aecd804fa16a.html and http://www.cisco.com/en/US/docs/ios/12_3t/12_3t4/feature/guide/gtrtlimt.html.

  Access Control List (ACL)

  An Access Control List (ACL) can be used to help mitigate attacks that target this vulnerability. ACLs can specify that only packets from legitimate sources are permitted to reach a device, and all others are to be dropped. The following example shows how to allow legitimate SSL sessions from trusted sources and deny all other SSL sessions:

  access-list 101 permit tcp host <legitimate_host_IP_address> host 
     <router_IP_address> eq 443
  access-list 101 deny tcp any any eq 443

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.

  Each row of the Cisco IOS software table (below) names a Cisco IOS release train. If a given release train is vulnerable, then the earliest possible releases that contain the fix (along with the anticipated date of availability for each, if applicable) are listed in the "First Fixed Release" column of the table. The "Recommended Release" column indicates the releases which have fixes for all the published vulnerabilities at the time of this Advisory. A device running a release in the given train that is earlier than the release in a specific column (less than the First Fixed Release) is known to be vulnerable. Cisco recommends upgrading to a release equal to or later than the release in the "Recommended Releases" column of the table.

  Major Release	Availability of Repaired Releases
  Affected 12.0-Based Releases	First Fixed Release	Recommended Release
  There are no affected 12.0 based releases
  Affected 12.1-Based Releases	First Fixed Release	Recommended Release
  There are no affected 12.1 based releases
  Affected 12.2-Based Releases	First Fixed Release	Recommended Release
  There are no affected 12.2 based releases
  Affected 12.3-Based Releases	First Fixed Release	Recommended Release
  There are no affected 12.3 based releases
  Affected 12.4-Based Releases	First Fixed Release	Recommended Release
  12.4	12.4(17a) 12.4(18)	12.4(18c)
  12.4JA	Not Vulnerable
  12.4JK	Not Vulnerable
  12.4JL	Not Vulnerable
  12.4JMA	Not Vulnerable
  12.4JMB	Not Vulnerable
  12.4JMC	Not Vulnerable
  12.4JX	Not Vulnerable
  12.4MD	Not Vulnerable
  12.4MR	12.4(19)MR	12.4(19)MR
  12.4SW	Not Vulnerable
  12.4T	Not Vulnerable
  12.4XA	Not Vulnerable
  12.4XB	Not Vulnerable
  12.4XC	Not Vulnerable
  12.4XD	Not Vulnerable
  12.4XE	Not Vulnerable
  12.4XF	Not Vulnerable
  12.4XG	Not Vulnerable
  12.4XJ	Not Vulnerable
  12.4XK	Not Vulnerable
  12.4XL	Not Vulnerable
  12.4XM	Not Vulnerable
  12.4XN	Not Vulnerable
  12.4XP	Not Vulnerable
  12.4XQ	Not Vulnerable
  12.4XT	Not Vulnerable
  12.4XV	Not Vulnerable
  12.4XW	Not Vulnerable
  12.4XY	Not Vulnerable
  12.4XZ	Not Vulnerable

Exploitation and Public Announcements

• The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-ssl

Revision History

• Revision 1.1	2009-April-16	Removed references to the combined software table, as it is now outdated
  Revision 1.0	2008-September-24	Initial public release

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