‘Cisco VPN 5000 Series Concentrator RADIUS PAP Authentication Vulnerability’

Summary

‘When a VPN 5000 series concentrator is configured to use a Remote Authentication Dial In User Service (RADIUS) server to authenticate client connections and the challenge type chosen is Password Authentication Protocol (PAP) or Challenge (a hybrid of PAP), the validation retry request sent to the RADIUS server when validation fails the first time does not have the user password field encrypted and so the password is sent as clear text. A VPN 5000 series concentrator configured to use Challenge-Handshake Authentication Protocol (CHAP) to authenticate is not affected by this vulnerability.

This vulnerability is documented as Cisco bug ID CSCdx82483. There are workarounds available to mitigate the affects of this vulnerability.’

Credit:

‘The information has been provided by Cisco Systems Product Security Incident Response Team.’


Details

Affected Products:
All Cisco VPN 5000 series concentrator hardware running software release 6.0.21.0002 (and earlier) and 5.2.23.0003 (and earlier) are affected by this vulnerability. This series includes models 5001, 5002, and 5008.

The older IntraPort series concentrator hardware is also affected by this vulnerability. This series includes models IntraPort 2, IntraPort 2+, IntraPort Enterprise-2 and Enterprise-8, IntraPort Carrier-2, and Carrier-8.

The VPN 3000 series concentrator hardware is not affected.

No other Cisco product is currently known to be affected by this vulnerability.

To determine your software revision, check the revision via the command line interface using the show version command.

Details:
Cisco VPN 5000 series concentrator hardware running software release 6.0.21.0002 (and earlier) and 5.2.23.0003 (and earlier), accepting clients using PAP authentication, aggressive mode (AM), or hybrid IKE Extended Authentication (XAUTH) mode, and validating against a RADIUS server, are affected by this vulnerability.

The VPN 5000 series concentrator supports three (3) RADIUS communication types. The [ RADIUS ] section keyword ChallengeType can be set to either CHAP, PAP, or Challenge. Challenge is a proprietary type of PAP used for Axent Defender authentication.

In case PAP or Challenge is configured, the remote device sends an authentication request to the VPN 5000 series concentrator containing its name and password. The VPN 5000 series concentrator uses either its internal database or a RADIUS server to validate the request and returns an authentication success or failure packet.

In the event that a RADIUS server is being used, the Access-Request is sent to the RADIUS server and the user password is encrypted as specified by the RFC. If the Access-Accept packet is not returned in a specific time, due to network or configuration problems, the concentrator sends out a retry packet but the user password is sent as clear text in this retry packet.

This vulnerability is documented as Cisco bug ID CSCdx82483, which requires a CCO account to view and can be viewed after 2002 August 8 at 1500 UTC.

Impact
During the password validation against a RADIUS server the PAP authentication password, in retry packets, is sent in the clear instead of being encrypted. This allows the password to be sniffed off the network(s) connecting the VPN 5000 series concentrator and the RADIUS server.

Software Versions and Fixes:
This vulnerability has been fixed in software release 6.0.21.0003 (and later) and 5.2.23.0004 (and later).

The procedure to upgrade to the fixed software version is detailed at http://www.cisco.com/univercd/cc/td/doc/product/aggr/vpn5000/5000sw/conce60x/5000cfg/swinst.htm.

Obtaining Fixed Software:
Cisco is offering free software upgrades to address this vulnerability for all affected customers. Customers may only install and expect support for the feature sets they have purchased.

Customers with service contracts should contact their regular update channels to obtain the free software upgrade identified via this advisory. For most customers with service contracts, this means that upgrades should be obtained through the Software Center on Cisco’s worldwide website at http://www.cisco.com/public/sw-center/.

Customers whose Cisco products are provided or maintained through a prior or existing agreement with third-party support organizations such as Cisco Partners, authorized resellers, or service providers should contact that support organization for assistance with obtaining the free software upgrade(s).

Customers who purchased directly from Cisco but who do not hold a Cisco service contract, and customers who purchase through third party vendors but are unsuccessful at obtaining fixed software through their point of sale, should obtain fixed software by contacting the Cisco Technical Assistance Center (TAC) using the contact information listed below. In these cases, customers are entitled to obtain an upgrade to a later version of the same release or as indicated by the applicable corrected software version in the Software Versions and Fixes section (noted above).

Cisco TAC contacts are as follows:
 * +1 800 553 2447 (toll free from within North America)
 * +1 408 526 7209 (toll call from anywhere in the world)
 * e-mail: tac@cisco.com

See http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional TAC contact information, including special localized telephone numbers and instructions and e-mail addresses for use in various languages.

Please have your product serial number available and give the URL of this advisory as evidence of your entitlement to a free upgrade.

Please do not contact either ‘psirt@cisco.com’ or ‘security-alert@cisco.com’ for software upgrades.

Workarounds:
One workaround is to only use CHAP for authentication by setting ChallengeType = CHAP in the [ RADIUS ] section.

If you have to use PAP for authentication, you can set the PrimRetries keyword to a value of 1 in the Radius section of the configuration. This would disable any retry attempts. In addition, if a second (backup) RADIUS server is defined with SecAddress, it must be removed, as the first attempt to a secondary RADIUS server will have the password in the clear.

For a complete fix, please upgrade to a fixed software version of code.’

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