CVE-2021-3634: debian debian_linux Out-of-bounds Write

Vulnerability summary

CVE-2021-3634 is a medium (CVSS 6.5) Out-of-bounds Write vulnerability in debian debian_linux. EPSS estimates a 4.68% chance of exploitation in the next 30 days, higher than 91.6% of scored vulnerabilities.

Timeline

1. 31-08-2021
   PublishedVulnerability first disclosed.
2. 03-08-2024
   Last modifiedVulnerability information updated.

Description

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.

• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.