CVE-2026-86219: Authen::SASL::Perl::DIGEST_MD5 versions before 2.2100 for Perl accept replayed authentication responses via unverified nonce in server_step
Authen::SASL::Perl::DIGESTMD5 versions before 2.2100 for Perl accept replayed authentication responses via unverified nonce in serverstep.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
debian/libauthen-sasl-perlto a version that resolves this vulnerability.Fixed in 2.2000-2 - Upgrade
Upgrade
Authen::SASL::Perl::DIGEST_MD5to a version that resolves this vulnerability.Fixed in 2.2100
Event History
Frequently Asked Questions
What does an attacker need to exploit this issue?
The attacker must observe one successful DIGEST-MD5 authentication exchange using qop=auth. They can then replay the captured response in a later session for the same service, host, realm, and user without knowing that user's password.
Which authentication attempts are susceptible to replay?
A captured first response with nc=00000001 can pass replay checks because the count table is keyed by the nonce supplied by the client and begins empty for each new server object. The issue affects versions before 2.2100.
Why does a new server challenge not prevent the replay?
Although server_start generates a fresh nonce, server_step does not verify that the nonce returned by the client matches that challenge. It instead calculates the expected digest using client-supplied parameters, allowing a digest to validate against the replayed response's own nonce.