A flaw in libssh's key derivation function, triggered when built with OpenSSL before version 3.0, causes the library to misinterpret success and failure codes. When key derivation fails, the function returns a success status, allowing an SSH session to proceed with uninitialized key material. This reuse of invalid keys can undermine the encryption used by the session, leading to confidentiality, integrity, and availability problems for the affected SSH connections. The weakness is a classic incorrect error handling flaw, mapped to CWE-682.

This vulnerability applies to any system that ships an older build of libssh linked to OpenSSL below 3.0. Red Hat Enterprise Linux 6, 7, 8, 9, 10, as well as the 9.0 Update Services for SAP Solutions, are all affected. Red Hat OpenShift Container Platform 4 also contains the vulnerable libssh component, and standalone libssh libraries distributed with older OpenSSL versions are impacted as well.

The CVSS score of 5.0 indicates medium severity. The EPSS score of less than 1% suggests a very low current exploitation probability, and the vulnerability is not listed in the CISA KEV catalog. Because the flaw lies at the core of SSH key establishment, a remote attacker able to manipulate the key exchange could potentially hijack or downgrade sessions. The attack vector is inferred to be remote, involving malicious SSH clients or servers that trigger the mis‑handled key derivation. Systems using the affected library remain vulnerable until patched or rebuilt against a recent OpenSSL.