Cisco Security Advisory: Multiple SSH Vulnerabilities

Document ID: 8118

Advisory ID: cisco-sa-20010627-ssh

http://www.cisco.com/warp/public/707/cisco-sa-20010627-ssh.shtml

Revision 1.6

Last Updated 2001 November 12 2030 UTC (GMT)

For Public Release 2001 June 27 1500 UTC (GMT)

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Contents

Summary
Affected Products
Details
Impact
Software Versions and Fixes
Workarounds
Obtaining Fixed Software
Exploitation and Public Announcements
Status of This Notice: FINAL
Distribution
Revision History
Cisco Security Procedures

Summary

Four different Cisco product lines are susceptible to multiple vulnerabilities discovered in the Secure Shell (SSH) protocol version 1.5. These issues have been addressed, and fixes have been integrated into the Cisco products that support this protocol.

By exploiting the weakness in the SSH protocol, it is possible to insert arbitrary commands into an established SSH session, collect information that may help in brute force key recovery, or brute force a session key.

Affected product lines are:

• All devices running Cisco IOS® software supporting SSH. This includes routers and switches running Cisco IOS software.
  
• Catalyst 6000 switches running CatOS.
  
• Cisco PIX Firewall.
  
• Cisco 11000 Content Service Switch family.
  

No other Cisco products are vulnerable. It is possible to mitigate this vulnerability by preventing, or having control over, the interception of SSH traffic.

Cisco IOS is not vulnerable to any of known exploits that are currently used to compromise UNIX hosts. For the warning regarding increased scanning activity for hosts running SSH consult CERT/CC

This advisory will be posted at: http://www.cisco.com/warp/public/707/cisco-sa-20010627-ssh.shtml.

Affected Products

Vulnerable Products

The following table depicts the affected products categories.

Per product category, the following software releases are vulnerable:

Products Confirmed Not Vulnerable

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

Details

An implementation of SSH in multiple Cisco products are vulnerable to three different vulnerabilities. These vulnerabilities are:

• CRC-32 integrity check vulnerability -- This vulnerability has been described in a CORE SDI S.A. paper entitled "An attack on CRC-32 integrity checks of encrypted channels using CBC and CFB modes", which can be found at http://www.core-sdi.com/soft/ssh/ssh.pdf.
  In order for this attack to succeed, an attacker must possess one or two known ciphertext/plaintext pairs. This should not be difficult since every session starts with a greeting screen which is fixed and which can be determined. This also implies that an attacker must be somewhere along the session path in order to be able to sniff the session and collect corresponding ciphertext.
  For further technical details, see http://www.core-sdi.com/soft/ssh/ssh.pdf.
  While fixing this vulnerability, we have not made the implementation mistake described by VU#945216 (see http://www.kb.cert.org/vuls/id/945216) which is being actively exploited.
  
• Traffic analysis -- This issue has been described in an analysis jointly made by Dug Song and Solar Designer. It can be found at: http://www.openwall.com/advisories/OW-003-ssh-traffic-analysis.txt, and is entitled "Passive Analysis of SSH (Secure Shell) Traffic".
  To exploit this vulnerability, an attacker must be able to capture packets. When sending a packet using the SSH protocol, it is padded to the next 8-byte boundary, but the exact length of the data (without the padding) is sent unencrypted.
  The timing between packets may yield additional information, such as the relative position of a letter on the keyboard, but that depends on overall jitter in the network and the typing habits of the person.
  For additional information, please see http://www.openwall.com/advisories/OW-003-ssh-traffic-analysis.txt.
  
• Key recovery in SSH protocol 1.5 -- This has been discovered by CORE SDI S.A. and the paper describing it can be viewed at http://www.securityfocus.com/archive/1/161150. The subject line is "SSH protocol 1.5 session key recovery vulnerability".
  In order to exploit this vulnerability, an attacker must be able to sniff the SSH session and be able to establish a connection to the SSH server. In order to recover the server key, an attacker must perform an additional 2^20+2^19=1572864 connections. Since the key has a lifespan of about an hour, this means that an attacker must perform around 400 connections per second.
  For further details, please see http://www.securityfocus.com/archive/1/161150.
  

Impact

This section describes the impact of these vulnerabilities.

• CRC-32 integrity check vulnerability -- By exploiting this protocol weakness, the attacker can insert arbitrary commands in the session after the session has been established.
  
• Traffic analysis -- This vulnerability exposes the exact lengths of the passwords used for login authentication. This is only applicable to an interactive session that is being established over the tunnel protected by SSH. This can significantly help an attacker in guessing the password using the brute force attack.
  
• Key recovery in SSH protocol 1.5 -- This vulnerability may lead to the compromise of the session key. Once the session key is determined, the attacker can proceed to decrypt the stored session using any implementation of the crypto algorithm used. This will reveal all information in an unencrypted form.
  

Software Versions and Fixes

The following software releases contain fixes for all vulnerabilities.

For CSS 11000 family, all vulnerabilities are fixed in the following software releases:

For Catalyst 6000 switches, all vulnerabilities are fixed in the following CatOS releases.

Each row of the table 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 and the anticipated date of availability for each are listed in the "Rebuild", "Interim", and "Maintenance" columns. A device running any release in the given train that is earlier than the release in a specific column (less than the earliest fixed release) is known to be vulnerable, and it should be upgraded at least to the indicated release or a later version (greater than the earliest fixed release label).

When selecting a release, keep in mind the following definitions:

• Maintenance
  Most heavily tested and highly recommended release of any label in a given row of the table.
  
• Rebuild
  Constructed from the previous maintenance or major release in the same train, it contains the fix for a specific defect. Although it receives less testing, it contains only the minimal changes necessary to effect the repair.
  
• Interim
  Built at regular intervals between maintenance releases and receives less testing. Interims should be selected only if there is no other suitable release that addresses the vulnerability, and interim images should be upgraded to the next available maintenance release as soon as possible. Interim releases are not available through manufacturing, and usually they are not available for customer download from CCO without prior arrangement with the Cisco TAC.
  

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 TAC for assistance as shown in the following section.

More information on Cisco IOS software release names and abbreviations is available at http://www.cisco.com/warp/public/620/1.html.

For PIX Firewall software, use the following table to determine affected and fixed software releases.

For Cisco IOS software, use the following table to determine affected and fixed software releases.

Workarounds

There are no workarounds for these vulnerabilities.

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 http://www.cisco.com/public/sw-license-agreement.html, or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

Do not contact either "psirt@cisco.com" or "security-alert@cisco.com" 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 http://www.cisco.com.

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 at obtaining fixed software through their point of sale should get their upgrades 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: tac@cisco.com
  

Have your product serial number available and give the URL of this notice as evidence of your entitlement to a free upgrade. Free upgrades for non-contract customers must be requested through the TAC.

Refer to 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.

Exploitation and Public Announcements

All three vulnerabilities are publicly known. Please see the Details section for the original announcements.

The Cisco PSIRT is not aware of malicious use of the vulnerabilities described in this advisory.

Status of This Notice: FINAL

Distribution

This advisory will be posted on Cisco's Worldwide Web site at http://www.cisco.com/warp/public/707/cisco-sa-20010627-ssh.shtml. 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:

• cust-security-announce@cisco.com
  
• bugtraq@securityfocus.com
  
• first-teams@first.org (includes CERT/CC)
  
• cisco@spot.colorado.edu
  
• comp.dcom.sys.cisco
  
• firewalls@lists.gnac.com
  
• 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

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 Web site at http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco Security Advisories are available at http://www.cisco.com/go/psirt.

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