CVE-2025-5987

A flaw was found in libssh when using the ChaCha20 cipher with the OpenSSL library. If an attacker manages to exhaust the heap space, this error is not detected and may lead to libssh using a partially initialized cipher context. This occurs because the OpenSSL error code returned aliases with the SSH_OK code, resulting in libssh not properly detecting the error returned by the OpenSSL library. This issue can lead to undefined behavior, including compromised data confidentiality and integrity or crashes.

Red Hat Product Security Team has rated this vulnerability as having a Moderate security impact. This is due to the high complexity in exploiting this flaw. For a successful attack to take place an attacker needs to manage to exhaust the heap space to for the OpenSSL library to return the error code which wrongly match the SSH_OK return code.

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.

A workaround for this issue is to disable the [email protected] cipher in applications using libssh when libssh is compiled with the OpenSSL backend, so the vulnerable ChaCha20-Poly1305 initialization path is not used. Alternatively, upgrade to a version of libssh containing the fix; upstream has released libssh 0.11.2 to correct this defect, and administrators are advised to upgrade or apply the upstream patch as soon as possible.