Cisco Security Advisory-
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 https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20011003-pix-firewall-auth-flood.
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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.
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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.
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There is no known workaround for all authentication types.
If authentication is configured in conjunction with the Virtual HTTP feature, a limit of three concurrent authentication attempts per user exists, which could prevent this denial of service for HTTP traffic only. This would have no effect on authentication attempts for FTP or Telnet if the PIX is configured for authentication of those services.
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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 including version 4.4(8)
Upgrade to 5.2(6)
Version 5.0 and Version 5.1
Upgrade to 5.2(6)
Version 5.2(2)
5.2(5.204)
5.2.(6)
Version 5.3.x up to and including version 5.3(1)
5.3(1.203)
5.3(2)
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This vulnerability has been publicly discussed on the Bugtraq list maintained by SecurityFocus at http://www.securityfocus.com/archive/1/174577
. Cisco has no
evidence or knowledge of exploitation of this vulnerability; this was
discovered when a program on a customer site utilized all authentication
resources.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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