Vulnerability Note VU#161576

Certain implementations of SSH1 may reveal internal cryptologic state

Overview

An implementation problem in at least one Secure Shell (SSH) product and a weakness in the PKCS#1_1.5 public key encryption standard allows attackers to recover plaintext of messages encrypted with SSH.

I. Description

A weakness in some SSH products using the SSH1 protocol may allow an attacker to determine internal cryptologic states. Combined with a weakness in the PKCS#1_1.5 public key encryption standard, used by SSH protocol 1.5, this vulnerability may be exploited to recover arbitrary session keys used for symmetric encryption in SSH connections. It has been reported that these vulnerabilities are relatively difficult to exploit.

II. Impact

An attacker may recover an SSH connection's session key and decrypt all communications from the connection.

III. Solution

Apply a patch available from your vendor

This vulnerability was first reported and patched in early 2001.
Reduce potential exposure

Disable all variants of SSH protocols 1.5 and older on the server.

Systems Affected

Vendor	Status	Date Notified	Date Updated
OpenSSH	Vulnerable	7-Jun-2002
SSH Communications Security	Unknown	12-Jun-2002

References

http://www.securityfocus.com/bid/2344
http://securityportal.com/articles/magicnumbers20010227.html

Credit

Thanks to CORE SDI for reporting this vulnerability and to Markus Friedl and Tatu Ylonen for their helpful clarifications.

This document was written by Shawn Van Ittersum.

Other Information

Date Public:	2001-02-13
Date First Published:	2002-07-31
Date Last Updated:	2002-07-31
CERT Advisory:
CVE-ID(s):
NVD-ID(s):
US-CERT Technical Alerts:
Metric:	6.48
Document Revision:	19

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