CVE-2021-3634 Information

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.

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Reference

https://bugzilla.redhat.com/show_bug.cgi?id=1978810 https://www.debian.org/security/2021/dsa-4965 https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/SVWAAB2XMKEUMPMDALINKAA4U2QM4LNG/ https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/JKYD3ZRAMDAQX3ZW6THHUF3GXN7FF6B4/ https://security.netapp.com/advisory/ntap-20211004-0003/ https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/DRK67AJCWYYVAGF5SGAHNZXCX3PN3ZFP/ https://www.oracle.com/security-alerts/cpujan2022.html

Attack Complexity

LOW

Privileges Required

LOW

User Interaction Required

LOW

Scope

NONE

Confidentiality Impact

UNCHANGED

Integrity Impact

NONE

Availability Impact

NONE

Base Score

HIGH

Base Severity

6.5