Cisco PIX Vulnerabilities

Summary

• This advisory documents two vulnerabilities for the Cisco PIX firewall. These vulnerabilities are documented as CSCeb20276 (SNMPv3) and CSCec20244 (VPNC).

  There are workarounds available to mitigate the effects of CSCeb20276 (SNMPv3). No workaround is available for CSCec20244 (VPNC).

  This advisory will be posted at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20031215-pix.

Affected Products

• This section provides details on affected products.

  Vulnerable Products

  All Cisco PIX firewall devices running the affected Cisco PIX firewall software, as documented below, are affected by these vulnerabilities.

  • CSCeb20276 (SNMPv3)
    6.3.1, 6.2.2 and earlier, 6.1.4 and earlier. 5.x.x and earlier.
    
  • CSCec20244 (VPNC)
    6.2 (2.119) to 6.2.3, both inclusive.
    6.3.x and 6.2.1 to 6.2 (2.118) are not affected.
    

  The Firewall Service Module (FWSM) is also vulnerable to the SNMPv3 issue and is documented as http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20031215-fwsm. No other Cisco products are currently known to be affected by these vulnerabilities.

  To determine your software revision, type show version at the command line prompt.

  Products Confirmed Not Vulnerable

  No other Cisco products are currently known to be affected by these vulnerabilities.

Details

• This section provides detailed information about these vulnerabilities.

  • CSCeb20276 (SNMPv3)
    The Cisco PIX firewall crashes and reloads while processing a received SNMPv3 message when snmp-server host or snmp-server host poll is configured on the Cisco PIX firewall. This happens even though the Cisco PIX firewall does not support SNMPv3.
    A Cisco PIX firewall configured to only generate and send traps using the snmp-server host trap command is not vulnerable.
    
  • CSCec20244 (VPNC)
    Under certain conditions an established VPNC IPSec tunnel connection is dropped if another IPSec client attempts to initiate an IKE Phase I negotiation to the outside interface of the VPN Client configured Cisco PIX firewall.
    Only a Cisco PIX firewall configured as a VPN Client is vulnerable to this vulnerability. A device reload of the VPN Client configured PIX is required to recover from this unstable state. No action is required on the headend VPN concentrator.
    A VPNC, also referred to as Easy VPN or ezVPN, connection is created when the Cisco PIX firewall is used as a VPN client to connect to a VPN server. An IKE Phase I negotiation is a step in the establishment of an IPSec session.
    CSCec20244 resolved this issue for the 6.2 (3.100) and later software releases.
    

  The Internetworking Terms and Cisco Systems Acronyms online guides can be found at http://www.cisco.com/univercd/cc/td/doc/cisintwk/.

  These vulnerabilities are documented in the Cisco Bug Toolkit as Bug ID CSCeb20276 (SNMPv3) and CSCec20244 (VPNC). To access this tool, you must be a registered user and you must be logged in.

Workarounds

• This section describes workarounds for these vulnerabilities.

  • CSCeb20276 (SNMPv3)
    There are two workarounds available.
    - If SNMP polling to the PIX is required on a vulnerable image, one may choose to restrict the polling access to the SNMP server to trusted interfaces and trusted hosts by using this command:
    snmp-server host poll
    

    Note: Both Poll and Trap are enabled if one does not specifically use the poll or trap keyword in the command above. The above command cannot prevent a source IP spoofed SNMP request message from exploiting this vulnerability. Prior to software version 6.0, one cannot selectively enable poll and trap functionality because there are no Poll and Trap keywords in the snmp-server host command.

    - Disable the SNMP server on the Cisco PIX firewall as follows:
    clear snmp-server
    no snmp-server location
    no snmp-server contact
    snmp-server community public
    no snmp-server enable traps
    

    Note: The Cisco PIX firewall does not allow one to remove the community string altogether. It will always be either public or a user configured string. show snmp will still show snmp-server community public, but this does not mean SNMP is enabled.

    More details at http://www.cisco.com/en/US/docs/security/pix/pix62/command/reference/s.html#wp1026423.
    
  • CSCec20244 (VPNC)
    No workaround. Please upgrade.
    

  The Cisco PSIRT recommends that affected users upgrade to a fixed software version of code.

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.

  • CSCeb20276 (SNMPv3)
    6.3.2 and later, 6.2.3 and later, 6.1.5 and later.
    
  • CSCec20244 (VPNC)
    6.3.1 and later, 6.2(3.100) and later.
    

  The procedure to upgrade to the fixed software version is detailed at http://www.cisco.com/univercd/cc/td/doc/product/iaabu/pix/pix_sw/index.htm.

Exploitation and Public Announcements

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

  CSCeb20276 (SNMPv3) was reported to the PSIRT by Rasto Rickardt.

URL

• http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20031215-pix

Revision History

• Revision 1.2	2004-January-26	Removed reference to CSCea28896, as it did not affect any released software. Added elaborative text to the SNMPv3 workaround section.
  Revision 1.1	2003-December-17	Added clear snmp-server command to the disable SNMP server workaround. Added elaborative text to the SNMPv3 details and workarounds sections.
  Revision 1.0	2003-December-15	Initial public release.

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