CVE-2026-86219

01/Description

Authen::SASL::Perl::DIGEST_MD5 versions before 2.2100 for Perl accept replayed authentication responses via unverified nonce in server_step. server_start generates a fresh nonce and sends it in the challenge, and nothing later compares that value against the nonce the client returns. server_step 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.

02/References6

• datatracker.ietf.org/doc/html/rfc2831#section-2.1.2
• github.com/perl-authen-sasl/perl-authen-sasl/commit/94337367030…
• metacpan.org/release/EHUELS/Authen-SASL-2.2000/source/lib/Authe…
• metacpan.org/release/EHUELS/Authen-SASL-2.2000/source/lib/Authe…
• metacpan.org/release/EHUELS/Authen-SASL-2.2100/changes
• www.cve.org/CVERecord?id=CVE-2025-40918