CVE-2021-3634

Published: 26 August 2021

A flaw has been found in libssh in versions prior to 0.9.6. The SSH protocol keeps track of two shared secrets during the lifetime of the session. One of them is called secret_hash and the other session_id. Initially, both of them are the same, but after key re-exchange, previous session_id is kept and used as an input to new secret_hash. Historically, both of these buffers had shared length variable, which worked as long as these buffers were same. But the key re-exchange operation can also change the key exchange method, which can be based on hash of different size, eventually creating "secret_hash" of different size than the session_id has. This becomes an issue when the session_id memory is zeroed or when it is used again during second key re-exchange.

Priority

Medium

CVSS 3 base score: 6.5

Status

Package Release Status
libssh
Launchpad, Ubuntu, Debian
Upstream
Released (1.9.6)
Ubuntu 21.04 (Hirsute Hippo)
Released (0.9.5-1ubuntu0.1)
Ubuntu 20.04 LTS (Focal Fossa)
Released (0.9.3-2ubuntu2.2)
Ubuntu 18.04 LTS (Bionic Beaver) Not vulnerable
(0.8.0~20170825.94fa1e38-1ubuntu0.7)
Ubuntu 16.04 ESM (Xenial Xerus) Not vulnerable

Ubuntu 14.04 ESM (Trusty Tahr) Does not exist