The flaw lies in the golang.org/x/crypto/ssh/knownhosts package where a revoked “SignatureKey” of a certificate authority was not properly verified against its “@revoked” status. As a result, the library could accept a key whose signature key was revoked. This allows a host key verification bypass that undermines the authentication step of an SSH client.

Any Go application that relies on the golang.org/x/crypto/ssh/knownhosts library for SSH host key validation and is running a pre‑fix version of the library is affected. The vulnerability applies to all releases before the patch that introduced revocation checks for both the key and its signature key. No specific version numbers are provided, so all older library builds should be considered at risk.

The CVSS score of 9.1 indicates a high severity, while an EPSS score of 7% suggests a moderate probability of exploitation. The likely attack vector is remote: an attacker would need to supply a revoked CA key to the SSH client’s host key verification flow. The vulnerability is not listed in CISA’s KEV catalog.