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Cisco Security Advisory

Cisco FWSM Vulnerabilities

Advisory ID: cisco-sa-20031215-fwsm

Revision 1.1

For Public Release 2003 December 15 16:00  UTC (GMT)


This advisory documents two vulnerabilities for the Cisco Firewall Services Module for Cisco Catalyst 6500 Series and Cisco 7600 Series (FWSM). These vulnerabilities are documented as CSCeb16356 (HTTP Auth) and CSCeb88419 (SNMPv3).

There are workarounds available to mitigate the effects of CSCeb88419 (SNMPv3). No workaround is available for CSCeb16356 (HTTP Auth).

Cisco has made free software available to address this issue for affected customers.

This advisory is posted at

Affected Products

Vulnerable Products

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

  • CSCeb16356 (HTTP Auth)
    1.1.2 and earlier.
  • CSCeb88419 (SNMPv3)
    1.1.2 and earlier.

The Cisco PIX firewall is also vulnerable to the SNMPv3 issue and is documented as 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.


  • CSCeb16356 (HTTP Auth)
    The Cisco FWSM may crash and reload due to a buffer overflow vulnerability while processing HTTP traffic requests for authentication using TACACS+ or RADIUS. This request is initiated when a user starting a connection via FTP, Telnet, or over the World Wide Web (HTTP) is prompted for their user name and password. If the user name and password are verified by the designated TACACS+ or RADIUS authentication server, the Cisco FWSM will allow further traffic between the authentication server and the connection to interact independently through the Cisco FWSM's "cut-through proxy" feature.
  • CSCeb88419 (SNMPv3)
    The Cisco FWSM crashes and reloads while processing a received SNMPv3 message when snmp-server host <if_name> <ip_addr> or snmp-server host <if_name> <ip_addr> poll is configured on the Cisco FWSM. This happens even though the Cisco FWSM does not support SNMPv3.
    A Cisco FWSM configured to only generate and send traps using the snmp-server host <if_name> <ip_addr> trap command is not vulnerable.

The Internetworking Terms and Cisco Systems Acronyms online guides can be found at

These vulnerabilities are documented in the Cisco Bug Toolkit as Bug ID CSCeb16356 (HTTP Auth) and CSCeb88419 (SNMPv3). To access this tool, you must be a registered user and you must be logged in.

Vulnerability Scoring Details

Cisco has not provided scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS).  At the time of original publication, CVSS scoring in Cisco security publications was not yet adopted.


  • CSCeb16356 (HTTP Auth)
    This vulnerability can be exploited to initiate a Denial of Service attack on the Cisco FWSM.
  • CSCeb88419 (SNMPv3)
    This vulnerability can be exploited to initiate a Denial of Service attack on the Cisco FWSM.

Software Versions and Fixes

  • CSCeb16356 (HTTP Auth)
    1.1.3 and later.
  • CSCeb88419 (SNMPv3)
    1.1.3 and later.

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

When considering software upgrades, also consult 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.


  • CSCeb16356 (HTTP Auth)
    No workaround. Please upgrade.
  • CSCeb88419 (SNMPv3)
    There are two workarounds available.
    • If SNMP polling to the Cisco FWSM 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 <if_name> <ip_addr> 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.

    • Disable the SNMP server on the Cisco FWSM 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 FWSM 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

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

Obtaining Fixed Software

Cisco has released software updates that address these vulnerabilities. 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 or for software upgrades

Customers with Service Contracts

Customers with contracts should obtain software through their regular update channels. For most customers, software patches and bug fixes 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 agreements 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 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:

Customers should have the product serial number available and be prepared to 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 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.

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 is 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 and is posted to the following e-mail and Usenet news recipients.


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 1.1


Added clear snmp-server command to the disable SNMP server workaround. Added elaborative text to the SNMPv3 details and workarounds sections.

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

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