A vulnerability has been reported in OpenSSH, which potentially can be exploited by malicious people to disclose sensitive information.

The vulnerability is caused due to the improper handling of errors within an SSH session encrypted with a block cipher algorithm in the CBC (Cipher-Block Chaining) mode. This can be exploited to potentially disclose up to 32 plaintext bits from an arbitrary block of ciphertext.

NOTE: An attack has a low probability of success, an attempt resulting in the termination of the current SSH session.

Successful exploitation requires that an attacker is able to read and alter network data.

This is related to:
SA32740

The vulnerability is reported in version 4.7p1. Other versions may also be affected.

Solution
Allow only CTR (Counter) mode cipher algorithms (e.g. AES-CTR) to be used in an SSH session.

Provided and/or discovered by
Martin Albrecht, Kenny Paterson, and Gaven Watson from the Information Security Group at Royal Holloway, University of London, reported via CPNI

Changelog
Further details available to Secunia VIM customers

Original Advisory
Centre for the Protection of National Infrastructure (CPNI):
http://www.cpni.gov.uk/Docs/Vulnerability_Advisory_SSH.txt

OpenSSH:
http://openssh.org/txt/cbc.adv

Other references
Further details available to Secunia VIM customers

Deep Links
Links available to Secunia VIM customers