{"id":"CVE-2026-85751","published":"2026-09-21T16:17:25.070","lastModified":"2026-09-24T21:25:27.050","description":"Mailu is a mail server distributed as a set of Docker images. From Mailu 2.0 until 2024.06.55 and prior to Mailu helm-charts 2.7.3, deployments with PROXY_AUTH_WHITELIST configured but REAL_IP_HEADER unset trusted a client-controlled X-Forwarded-By header for header-based proxy authentication. The proxy_hide_header directive in the nginx template at core/nginx/conf/proxy.conf hid the header from upstream responses but did not overwrite the incoming request value in this configuration. An unauthenticated remote attacker could therefore spoof the trusted proxy identity and bypass authentication. This issue is fixed in Mailu 2024.06.55 and Mailu helm-charts 2.7.3.","cvssScore":9.8,"cvssSeverity":"CRITICAL","cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","cwes":["CWE-290","CWE-807"],"vendors":[],"products":[],"references":[{"url":"https://github.com/Mailu/Mailu/commit/dffa97cbd889ab208246372ce9c86e99abb27ae9","tags":[]},{"url":"https://github.com/Mailu/Mailu/commit/ff4003d045753013470945336448dbd790cac778","tags":[]},{"url":"https://github.com/Mailu/Mailu/pull/4070","tags":[]},{"url":"https://github.com/Mailu/Mailu/pull/4071","tags":[]},{"url":"https://github.com/Mailu/Mailu/releases/tag/2024.06.55","tags":[]},{"url":"https://github.com/Mailu/Mailu/security/advisories/GHSA-rfhj-4wcq-74xg","tags":[]}],"exploitRefs":[{"url":"https://github.com/Mailu/Mailu/commit/dffa97cbd889ab208246372ce9c86e99abb27ae9","tags":[]},{"url":"https://github.com/Mailu/Mailu/commit/ff4003d045753013470945336448dbd790cac778","tags":[]},{"url":"https://github.com/Mailu/Mailu/pull/4070","tags":[]},{"url":"https://github.com/Mailu/Mailu/pull/4071","tags":[]},{"url":"https://github.com/Mailu/Mailu/releases/tag/2024.06.55","tags":[]},{"url":"https://github.com/Mailu/Mailu/security/advisories/GHSA-rfhj-4wcq-74xg","tags":[]}],"hasPoc":true,"ai":{"summary":"The flaw allows an unauthenticated attacker to bypass authentication by spoofing the X-Forwarded-By header, which is critical for securing mail server deployments.","exploitability":"Exploitation is relatively straightforward if the attacker can control the X-Forwarded-By header and the REAL_IP_HEADER is not set, making it a significant risk.","blast_radius":"If exploited, this could lead to unauthorized access and potential data breaches, impacting the security and integrity of the mail server.","remediation":"Upgrade to Mailu 2024.06.55 or later, or ensure the REAL_IP_HEADER is properly configured to prevent header-based proxy authentication spoofing.","detection":"No reliable host or network indicator is derivable from the published description.","tags":["auth-bypass","header-spoofing","mail-server","nginx"],"model":"qwen2.5:7b-instruct","analyzedAt":"2026-09-27T08:59:54.175Z"}}