Products & Services
Support

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
Guest

Cisco Security Advisory

Multiple SSH Vulnerabilities

Advisory ID: cisco-sa-20010627-ssh

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010627-ssh

Revision 1.6

For Public Release 2001 June 27 15:00  UTC (GMT)


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 IOSĀ® 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 leavingcisco.com

This advisory will be posted at: http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010627-ssh.

Affected Products

Vulnerable Products

The following table depicts the affected products categories.

Product Category

CRC-32 check

Traffic analysis

Key recovery

IOS

Vulnerable CSCdt96253

Vulnerable CSCdt57231

Vulnerable CSCdu37371

PIX

Vulnerable CSCdt73353

Not vulnerable

Not vulnerable

VPN3000

Not vulnerable

Not vulnerable

Not vulnerable

Catalyst 6000

Vulnerable CSCdt72996

Vulnerable CSCdt55357

Not vulnerable

CSS 11000

Vulnerable CSCdv34668

Vulnerable CSCdv34676

Vulnerable CSCdv34679

Per product category, the following software releases are vulnerable:

IOS

All 12.0 and later releases that include support for SSH.

PIX

5.2(5) and 5.3.(1)

CatOS

6.2(0.110)

VPN3000

Not vulnerable

CSS 11000

All WebNS releases prior, but excluding, versions: R4.01 B42s, R4.10 B22s, R5.0 B11s, R5.01 B6s

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.

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
http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html .

Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at
http://intellishield.cisco.com/security/alertmanager/cvss .


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:

WebNS

R4.01 B42s, R4.10 B22s, R5.0 B11s, R5.01 B6s

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

CatOS

6.1(2.13), 6.2(0.111) and 6.3(0.7)PAN

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.

Train

Description of Image or Platform

Availability of Fixed Releases*

5.x-based Releases

Rebuild

Interim**

Maintenance

5.2

Early Deployment (ED) for all platforms

 

5.2(5)203 Available through TAC

5.2.(6) Available in August

5.3

Early Deployment (ED) for all platforms

 

5.3(1)202 Available through TAC

5.3.(2) Available in August

6.x-based Releases

Rebuild

Interim**

Maintenance

6.0

Early Deployment (ED) for all platforms

   

6.0(1) Available

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

Train

Description of Image or Platform

Availability of Fixed Releases*

12.0-based Releases

Rebuild

Interim**

Maintenance

12.0S

Core/ISP support: GSR, RSP, c7200

   

12.0(20)S 2001-November

12.1-based Releases

Rebuild

Interim**

Maintenance

12.1

General deployment release for all platforms

SSH not supported

12.1AA

Dial support

SSH not supported

12.1CX

Core/ISP support: GSR, RSP, c7200

SSH not supported

12.1DA

xDSL support: 6100, 6200

SSH not supported

12.1DB

Cisco IOS Software Release 12.1(1)DB supports Cisco?s 6400 Universal Access Concentrator

     

12.1DC

Cisco IOS Software Release 12.1(1)DC supports Cisco?s 6400 Universal Access Concentrator

     

12.1E

Core/ISP support: GSR, RSP, c7200

   

12.1(8a)E 2001-Jul-09

12.1EC

12.1EC is being offered to allow early support of new features on the uBR7200 platform, as well as future support for new Universal Broadband Router headend platforms.

 

12.1(6.5)EC3

 

12.1EX

Catalyst 6000 support

   

12.1(8a)E 2001-Jul-09

12.1EY

Cat8510c, Cat8510m, Cat8540c, Cat8540m, LS1010

   

12.1(6)EY

12.1EZ

Early Deployment (ED): special image

12.1(6)EZ2

   

12.1T

Early Deployment(ED): VPN, Distributed Director, various platforms

Not Scheduled

Upgrade recommended to 12.2(1b)

12.1XA

Early Deployment (ED): limited platforms

Not Scheduled

Upgrade recommended to 12.2(1b)

12.1XB

Early Deployment (ED): limited platforms

     

12.1XC

Early Deployment (ED): limited platforms

Not Scheduled

Upgrade recommended to 12.2(1b)

12.1XD

Early Deployment (ED): limited platforms

Not Scheduled

Upgrade recommended to 12.2(1b)

12.1XE

Early Deployment (ED): limited platforms

     

12.1XF

Early Deployment (ED): 811 and 813 (c800 images)

12.1(2)XF4 2001-July-09

   

12.1XG

Early Deployment (ED): 800, 805, 820, and 1600

12.1(2)XF4 2001-July-09

   

12.1XH

Early Deployment (ED): limited platforms

Not Scheduled

Upgrade recommended to 12.2(1b)

12.1XI

Early Deployment (ED): limited platforms

Not Scheduled

Upgrade recommended to 12.2(1b)

12.1XJ

Early Deployment (ED): limited platforms

Not Scheduled

Upgrade recommended to 12.1(5)YB4

12.1XK

Early Deployment (ED): limited platforms

SSH not supported

12.1XL

Early Deployment (ED): limited platforms

Not Scheduled

Upgrade recommended to 12.2(1b)

12.1XM

Short-lived early deployment release

12.1(4)XM4 2001-June-27

   

12.1XP

Early Deployment (ED): 1700 and SOHO

12.1(3)XP4

   

12.1XQ

Short-lived early deployment release

Not Scheduled

Upgrade recommended to 12.2(1b)

12.1XR

Short-lived early deployment release

12.1(5)XR2

   

12.1XS

Short-lived early deployment release

12.1(5)XS2 2001-July

   

12.1XT

Early Deployment (ED): 1700 series

12.1(3)XT3

   

12.1XU

Early Deployment (ED): limited platforms

12.1(5)XU1

   

12.1XV

Short-lived early deployment release

12.1(5)XV3 2001-July

   

12.1XW

Short-lived early deployment release

SSH not supported

12.1XX

Short-lived early deployment release

SSH not supported

12.1XY

Short-lived early deployment release

12.1(5)XY6 2001-July

   

12.1XZ

Short-lived early deployment release

SSH not supported

12.1YA

Short-lived early deployment release

Not Scheduled

Upgrade recommended to 12.2(2)XB 2001-August

12.1YB

Short-lived early deployment release

12.1(5)YB4

   

12.1YC

Short-lived early deployment release

12.1(5)YC1

   

12.1YD

Short-lived early deployment release

12.1(5)YD2 2001-June-25

   

12.1YF

Short-lived early deployment release

12.1(5)YF2

   

12.2-based Releases

Rebuild

Interim**

Maintenance

12.2

General deployment release for all platforms

12.2(1b)

12.2(1.1)

12.2(3) 2001-August

12.2T

General deployment release for all platforms

 

12.2(2.2)T

 

12.2XA

SPLOB

   

12.2(2)XA 2001-July-02

12.2XD

Short-lived early deployment release

12.2(1)XD1

   

12.2XE

Short-lived early deployment release

   

12.2(1)XE

12.2XH

Short-lived early deployment release

   

12.2(1)XH 2001-June-25

12.2XQ

Short-lived early deployment release

   

12.2(1)XQ 2001-June-23

Notes

* All dates are estimates and subject to change.

** Interim releases are subjected to less rigorous testing than regular maintenance releases, and may have serious bugs.


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

THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.

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.


Distribution

This advisory will be posted on Cisco's Worldwide Web site at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010627-ssh. 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

Revision 1.6

2001-Nov-12

Updated information regarding vulnerability of UNIX hosts in Summary section and implementation mistake VU#945216 in Details section

Revision 1.5

2001-Oct-05

Updated SSH protocol version information in Summary section

Revision 1.4

2001-Oct-04

Updated maintenance release version and date for Cisco IOS software 12.0S train in Software Versions and Fixes section

Revision 1.3

2001-Sept-20

Updated information regarding CSS in Summary, Affected Products and Software Versions and Fixes sections

Revision 1.2

2001-Aug-08

Updated url in Details section

Revision 1.1

2001-June-28

Updated software availability date; added Traffic Analysis author

Revision 1.0

2001-June-27

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 Web site at http://www.cisco.com/web/about/security/psirt/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.


Download this document (PDF)
View Printable Version