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Older SSH clients do not allow users to disable X11 forwarding

Vulnerability Note VU#118892

Original Release Date: 2001-10-26 | Last Revised: 2002-03-05

Overview

This vulnerability may allow an attacker to make unauthorized connections to affected client machines.

Description

Older versions of the SSH client do not allow the user to disable X11 forwarding. As a result, if the client connects to a malicious server, the server can open an X11 connection to the client's display without notifying the client. The attacker would then have access to the client's X11 session, which would permit activities such as keystroke monitoring.

It is also possible for an attacker to make X11 connections to the client by taking over the victim's TCP connection; however, this should generate a client-side warning about changed host keys. If the client responds to the prompt by breaking the connection, no keystrokes or sensitive data will be transmitted.

Impact

Attackers can make unauthorized connections to victim machines, potentially accessing sensitive data.

Solution

Upgrade to a version of SSH that allows X11 forwarding to be disabled.

Vendor Information

118892
Expand all

SSH Communications Security

Updated:  November 03, 2000

Status

  Vulnerable

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

OpenSSH

Updated:  October 29, 2001

Status

  Not Vulnerable

Vendor Statement

See http://www.openssh.com/security.html.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.


CVSS Metrics

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A

References

Credit

The CERT/CC thanks Antti Huima, Tuomas Aura, and Janne Salmi for their analysis and Tatu Ylonen for bringing this vulnerability to our attention.

This document was written by Jeffrey P. Lanza.

Other Information

CVE IDs: None
Severity Metric: 0.42
Date Public: 2001-01-18
Date First Published: 2001-10-26
Date Last Updated: 2002-03-05 22:52 UTC
Document Revision: 6

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