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OpenSSH CBC Mode Plaintext Recovery Vulnerability

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Release Date:  2008-11-17    Last Update:  2008-11-25    Views:  12,291

Secunia Advisory SA32760

Where:

From local network

Impact:

Exposure of sensitive information

Solution Status:

Unpatched

CVE Reference(s):

Description


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

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

Deep Links:
Links available to Secunia VIM customers

Do you have additional information related to this advisory?

Please provide information about patches, mitigating factors, new versions, exploits, faulty patches, links, and other relevant data by posting comments to this Advisory. You can also send this information to vuln@secunia.com

Subject: OpenSSH CBC Mode Plaintext Recovery Vulnerability

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