Cisco Security Advisory: Cisco PIX Firewall Authentication Denial of Service Vulnerability Document ID: 13635 Advisory ID: cisco-sa-20011003-pix-firewall-auth-flood http://www …… com/warp/public/707/cisco-sa-20011003-pix-firewall-auth-flood.shtml Revision 1.0 For Public Release 2001 October 03 1600 UTC (GMT) Please provide your feedback on this document. Summary Affected Products Details Impact Software Versions and Fixes Workarounds Obtaining Fixed Software Exploitation and Public Announcements Status of This Notice: …

Summary The Cisco Secure PIX Firewall AAA authentication feature, introduced in version 4.0, is vulnerable to a Denial of Service (DoS) attack initiated by authenticating users on the system. This vulnerability affects specific configurations and has been resolved in released versions of the PIX Firewall. This vulnerability has been assigned Cisco bug ID CSCdt92339. The complete notice will be available at http://www.cisco.com/warp/public/707/cisco-sa-20011003-pix-firewall-auth-flood.shtml. Affected Products This section provides details on affected products. Vulnerable Products All users of Cisco Secure PIX Firewalls with software versions 4.0 up to and including 4.4(8), 5.0(3), 5.1(3), 5.2(2), and 5.3(1) with configurations using AAA authentication are at risk. Affected configurations will have configuration lines that begin: pixfirewall# aaa authentication … Products Confirmed Not Vulnerable Configurations not including aaa authentication are not affected. PIX Firewall software versions 6.0(1) and later are not affected. The IOS Firewall feature set is not affected by the above defect. No other Cisco products are currently known to be affected by these vulnerabilities. Details When AAA authentication services are configured on the Cisco Secure PIX Firewall, it is possible for a single source address to consume all of the authentication resources, preventing other legitimate users from authenticating. This is a denial of service strictly for the authentication resources; other established traffic continues unaffected, and only new authentication requests are prevented. This vulnerability has been resolved in the recent versions of the PIX Firewall by creating a maximum limit of three open authentication requests per user. Cisco Bug ID CSCdv09731 amends this limitation to allow system administrators to modify this limit, depending on their network requirements. Impact This issue causes a PIX Firewall to be vulnerable to a DoS attack in which the availability of the unit is degraded. This does not result in a loss in confidentiality or in loss of integrity of the traffic being filtered. Software Versions and Fixes 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. Version Affected Interim Release Fix carries forward into all later versions Fixed Regular Release (available now) Fix carries forward into all later versions All versions of Cisco Secure PIX up to and Upgrade to 5.2(6)

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