CVE-2026-73636: Apache HTTP Server: mod_auth_digest one-time-nonce replay attack

Apache HTTP Server’s mod_auth_digest has an authentication bypass by capture-replay (CWE-294) on all platforms. A man-in-the-middle attacker who has already captured digest authentication credentials can replay them using crafted requests that force garbage collection of the client’s shared-memory entry, but only when AuthDigestNonceLifetime is set to 0. A successful replay lets the attacker authenticate as that client without knowing the password. Apache HTTP Server 2.4.x is affected in that configuration; version 2.4.69 fixes the issue. No public proof-of-concept is known, and the flaw is not listed in CISA’s Known Exploited Vulnerabilities catalog.

Upgrade Apache HTTP Server to 2.4.69. Until that is possible, do not set AuthDigestNonceLifetime to 0, or stop using mod_auth_digest and prefer a stronger authentication method over TLS. Review configs for digest authentication, since exploitation also requires a man-in-the-middle position on the client path.