Advisory ID: cisco-sa-20040317-openssl

Revision 1.6

For Public Release 2004 March 17 13:00  UTC (GMT)


Affected Products
Vulnerability Scoring Details
Software Versions and Fixes
Obtaining Fixed Software
Exploitation and Public Announcements
Status of this Notice: Final
Revision History
Cisco Security Procedures


A new vulnerability in the OpenSSL implementation for SSL has been announced on March 17, 2004.

An affected network device running an SSL server based on an affected OpenSSL implementation may be vulnerable to a Denial of Service (DoS) attack. There are workarounds available to mitigate the effects of this vulnerability on Cisco products in the workaround section of this advisory. Cisco is providing fixed software, and recommends that customers upgrade to it when it is available.

This advisory will be posted at

Affected Products

This section provides details on affected products.

Vulnerable Products

The following products have their SSL implementation based on the OpenSSL code and are affected by this vulnerability.

  • Cisco IOS 12.1(11)E and later in the 12.1E release train for the Cisco 7100 and 7200 Series Routers. Only crypto images (56i and k2) are vulnerable.
  • Cisco IOS 12.2SY and 12.2ZA release trains for the Cisco Catalyst 6500 Series and Cisco 7600 Series Routers. Only crypto images (k8, k9 and k91) are vulnerable.
  • Cisco PIX Firewall
  • Cisco Firewall Services Module (FWSM) for the Cisco Catalyst 6500 Series and Cisco 7600 Series routers
  • Cisco MDS 9000 Series Multilayer Switch
  • Cisco Content Service Switch (CSS) 11000 and 11500 series
  • Cisco Global Site Selector (GSS) 4480 and 4490
  • Cisco Content Service Switch (CSS) Secure Content Accelerator (SCA) versions 1 & 2
  • CiscoWorks Common Services (CWCS) version 2.2 and CiscoWorks Common Management Foundation (CMF) version 2.1
  • Cisco Access Registrar (CAR)
  • Cisco Call Manager (CCM)
  • Cisco Okena Stormwatch 3.2
  • Cisco Application & Content Networking Software (ACNS)
  • Cisco Threat Response (CTR)

The following products have their SSL implementation based on the OpenSSL code and are not affected by this vulnerability.

  • Cisco Secure Intrusion Detection System (NetRanger) appliance. This includes the IDS-42xx appliances, NM-CIDS and WS-SVS-IDSM2.
  • Cisco SN 5428 and SN 5428-2 Storage Router
  • Cisco CNS Configuration Engine
  • Cisco Network Analysis Modules (NAM) for the Cisco Catalyst 6000 and 6500 Series switches and Cisco 7600 Series routers
  • Cisco SIP Proxy Server (SPS)
  • CiscoWorks 1105 Hosting Solution Engine (HSE)
  • CiscoWorks 1105 Wireless LAN Solution Engine (WLSE)
  • Cisco Ethernet Subscriber Solution Engine (ESSE)

The following products, which implement SSL, are not affected by this vulnerability.

  • Cisco VPN 3000 Series Concentrators
  • Cisco Secure Socket Layer (SSL) Services Module for the Cisco Catalyst 6500 Series and Cisco 7600 Series routers

Products Confirmed Not Vulnerable

CatOS does not implement SSL and is not vulnerable.

No other Cisco products are currently known to be affected by these vulnerabilities.This vulnerability is still being actively investigated across Cisco products and status of some products has still not been determined.


Secure Sockets Layer (SSL), is a protocol used to encrypt the data transferred over a TCP session. SSL in Cisco products is mainly used by the HyperText Transfer Protocol Secure (HTTPS) web service for which the default TCP port is 443. The affected products, listed above, are only vulnerable if they have the HTTPS service enabled and the access to the service is not limited to trusted hosts or network management workstations. They are not vulnerable to transit traffic, only traffic that is destined to them may exploit this vulnerability.

To check if the HTTPS service is enabled one can do the following:

  1. Check the configuration on the device to verify the status of the HTTPS service.
  2. Try to connect to the device using a standard web browser that supports SSL using a URL similar to https://ip_address_of_device/.
  3. Try and connect to the default HTTPS port, TCP 443, using Telnet. telnet ip_address_of_device 443. If the session connects the service is enabled and accessible.

Testing by the OpenSSL development team has uncovered a null-pointer assignment in the do_change_cipher_spec() function. A remote attacker could perform a carefully crafted SSL/TLS handshake against a server that used the OpenSSL library in such a way as to cause OpenSSL to crash. This crash on many Cisco products would cause the device to reload. Repeated exploitation of this vulnerability would result in a Denial of Service (DoS) attack on the device.

Another flaw was also discovered in the SSL/TLS handshaking code when using Kerberos ciphersuites. A remote attacker could perform a carefully crafted SSL/TLS handshake against a server configured to use Kerberos ciphersuites in such a way as to cause OpenSSL to crash. None of the Cisco OpenSSL implementations are known to use Kerberos ciphersuites and are therefore not affected by this second vulnerability.

A third vulnerability described in the NISCC advisory is a bug in older versions of OpenSSL, versions before 0.9.6d, that can also lead to a Denial of Service attack. None of the Cisco OpenSSL implementations are known to be affected by this older OpenSSL issue.

More information on the OpenSSL vulnerability is available at

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

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 .


An affected network device running an SSL server based on the OpenSSL implementation may be vulnerable to a Denial of Service (DoS) attack.

Software Versions and Fixes

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.

Each row of the Cisco IOS software table (below) describes a release train and the platforms or products for which it is intended. If a given release train is vulnerable, then the earliest possible releases that contain the fix (the "First Fixed Release") and the anticipated date of availability for each are listed in the "Rebuild" and "Maintenance" columns. A device running a release in the given train that is earlier than the release in a specific column (less than the First Fixed Release) is known to be vulnerable. The release should be upgraded at least to the indicated release or a later version (greater than or equal to the First Fixed Release label).

For more information on the terms "Rebuild" and "Maintenance," consult the following URL:


The Cisco PSIRT recommends that affected users upgrade to a fixed software version of code as soon as it is available.

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 malicious use of the vulnerability described in this advisory.

This vulnerability was reported to Cisco PSIRT by NISCC. NISCC has documented this vulnerability at

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 8C82 5207 0CA9 ED40 1DD2 EE2A 7B31 A8CF 32B6 B590 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 1.6


Updated CTR and MDS 9000 fixed release information.

Revision 1.5


Added details for CWCS. Updated CSS fixed release information.

Revision 1.4


Added details for CCM and GSS, CSS and SCA.

Revision 1.3


Change availability date for FWSM. Added details for ACNS.

Revision 1.2


Added the IOS 12.2ZA release train, CSS SCA, ACNS, CTR, GSS 4490 and the CSS 11500 series to the affected product list. Added more details on the PIX.

Revision 1.1


Added CCM, Okena Stormwatch as affected. Added SSL module for 6500/7600 as not affected. Elaborated on the IOS releases in the Affected section.

Revision 1.0


Initial 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

This advisory is copyright 2004 by Cisco Systems, Inc. This advisory may be redistributed freely after the release date given at the top of the text, provided that redistributed copies are complete and unmodified, including all date and version information.