CVE-2025-5372 Libssh: incorrect return code handling in ssh_kdf() in libssh

Description

A flaw was found in libssh versions built with OpenSSL versions older than 3.0, specifically in the ssh_kdf() function responsible for key derivation. Due to inconsistent interpretation of return values where OpenSSL uses 0 to indicate failure and libssh uses 0 for success—the function may mistakenly return a success status even when key derivation fails. This results in uninitialized cryptographic key buffers being used in subsequent communication, potentially compromising SSH sessions' confidentiality, integrity, and availability.

Exploitable remotely over the network, with an ordinary account and without any user action; the impact on data or service is limited.

Attack vector

Network

Attack complexity

High

Privileges required

Low

Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

Low

Availability

Low

Affected products and versions