CVE-2025-5372

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.

The Red Hat Product Security team has assessed the severity of this vulnerability as Moderate due to the combination of limited prerequisites and its impact on confidentiality, integrity, and availability. The vulnerability is only present when libssh is built with OpenSSL versions older than 3.0. Successful exploitation could allow an attacker to initiate cryptographic operations using uninitialized keys, which may compromise secure SSH sessions.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this issue, administrators should ensure that libssh is built against OpenSSL version 3.0 or later. This change eliminates the return code mismatch and prevents the erroneous use of uninitialized key material. It is also strongly recommended to apply vendor supplied patches or update to the latest libssh security release as soon as possible.