The bug in golang.org/x/crypto/ssh caused the source-address critical option supplied by authentication callbacks to be enforced only for PublicKeyCallback and VerifiedPublicKeyCallback. Other callback methods—PasswordCallback, KeyboardInteractiveCallback, NoClientAuthCallback, and GSSAPIWithMICConfig.AllowLogin—were ignored during permission validation, meaning any source-address restriction these callbacks could impose was silently bypassed. This flaw allows an attacker who can influence or supply the authentication callback to craft permissions that grant access from an untrusted IP, effectively nullifying IP-based access controls that an SSH server might rely on.

Vendors: golang.org/x/crypto, product: golang.org/x/crypto/ssh. All releases of this SSH library that predate the patch are considered vulnerable; the CVE description does not list exact version numbers, so any version before the fix that contains the unpatched callback enforcement logic should be treated as at risk and updated to a newer release.

The vulnerability can be leveraged remotely by connecting to an SSH service that uses the vulnerable library and providing a malicious authentication callback. The CVSS score of 7.5 indicates high severity, and although no EPSS score is available, the lack of IP restriction enforcement dramatically increases the likelihood of successful exploitation. The vulnerability is not listed in the CISA KEV catalog. An attacker who can dictate the authentication callback—such as a developer of software that embeds this SSH library—could bypass source-address restrictions, gaining privileged access that should be denied. The dependence on the application to supply callbacks variants means that many real-world deployments using this library are potentially exposed.