Products & Services

Product Categories

Popular Downloads

Manage Software

How to Buy

For Home

Linksys Products Store
Linksys is now part of Belkin
Products for everyone

All Ordering Options

Training & Events Partners

Cisco Security Advisory

Cisco VPN 5000 Series Concentrator RADIUS PAP Authentication Vulnerability

Advisory ID: cisco-sa-20020807-vpn5k-radius-pap

Revision 1.0

For Public Release 2002 August 7 15:00  UTC (GMT)

Related Resources:

View related Alert


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.

This advisory will be posted at

Affected Products

This section provides details on affected products.

Vulnerable Products

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

The older IntraPort series concentrator hardware are 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.

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

Products Confirmed Not Vulnerable

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


Cisco VPN 5000 series concentrator hardware running software release (and earlier) and (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.

Vulnerability Scoring Details

Cisco has provided scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in this Security Advisory is done in accordance with CVSS version 2.0.

CVSS is a standards-based scoring method that conveys vulnerability severity and helps determine urgency and priority of response.

Cisco has provided a base and temporal score. Customers can then compute environmental scores to assist in determining the impact of the vulnerability in individual networks.

Cisco has provided an FAQ to answer additional questions regarding CVSS at .

Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at .


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 (and later) and (and later).

The procedure to upgrade to the fixed software version is detailed at


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. Also, 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.

Obtaining Fixed Software

Cisco has made free software available to address this vulnerability for affected customers. Prior to deploying software, customers should consult their maintenance provider or check the software for feature set compatibility and known issues specific to their environment.

Customers may only install and expect support for the feature sets they have purchased. By installing, downloading, accessing or otherwise using such software upgrades, customers agree to be bound by the terms of Cisco's software license terms found at, or as otherwise set forth at Downloads at

Do not contact either "" or "" for software upgrades.

Customers with Service Contracts

Customers with contracts should obtain upgraded software through their regular update channels. For most customers, this means that upgrades should be obtained through the Software Center on Cisco's worldwide website at

Customers Using Third-Party Support Organizations

Customers whose Cisco products are provided or maintained through prior or existing agreement with third-party support organizations such as Cisco Partners, authorized resellers, or service providers should contact that support organization for guidance and assistance with the appropriate course of action in regards to this advisory.

The effectiveness of any workaround or fix is dependent on specific customer situations such as product mix, network topology, traffic behavior, and organizational mission. Due to the variety of affected products and releases, customers should consult with their service provider or support organization to ensure any applied workaround or fix is the most appropriate for use in the intended network before it is deployed.

Customers Without Service Contracts

Customers who purchase direct from Cisco but who do not hold a Cisco service contract and customers who purchase through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain software patches and bug fixes by contacting the Cisco Technical Assistance Center (TAC). 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:

Have your product serial number available and provide the URL of this notice as evidence of entitlement to a software patch or bug fix. Customers without service contracts should request a software patch or bug fix through the TAC.

Refer to for additional TAC contact information, including special localized telephone numbers and instructions and e-mail addresses for use in various languages.

Exploitation and Public Announcements

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

This vulnerability was reported to PSIRT by a customer.

Status of This Notice: Final


A stand-alone copy or Paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors.


This advisory will be posted on Cisco's worldwide website at

In addition to worldwide web posting, a text version of this notice is clear-signed with the Cisco PSIRT PGP key having the fingerprint FEB1 1B89 A64B 60BB 4770 D1CE 93D2 FF06 F236 759C and is posted to the following e-mail and Usenet news recipients.

  • (includes CERT/CC)
  • Various internal Cisco mailing lists

Future updates of this advisory, if any, will be placed on Cisco's worldwide website, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the above URL for any updates.

Revision History

Revision 1.0


Initial public release.

Cisco Security Procedures

Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's worldwide website at This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at

Download this document (PDF)
View Printable Version