CVE-2026-86219

Authen::SASL::Perl::DIGESTMD5 versions before 2.2100 for Perl accept replayed authentication responses via unverified nonce in serverstep.

serverstart generates a fresh nonce and sends it in the challenge, and nothing later compares that value against the nonce the client returns. serverstep derives the expected digest from the client's own parameters, so a response verifies whenever its digest matches the nonce it carries. The count table it also checks is keyed on the client-supplied nonce and starts empty in each new server object, so a captured first response, carrying nc=00000001, passes that too. RFC 2831 defines the nonce in the response as the value the server sent in the preceding challenge.

An attacker who observes one successful qop=auth exchange can replay the captured response against a later session for the same service, host, realm and user, and authenticate as that user without knowing the password.