{"id":"CVE-2026-85751","published":"2026-09-21T16:17:25.070","lastModified":"2026-09-21T18:17:11.697","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 spoof trusted proxy identity and bypass authentication by manipulating the X-Forwarded-By header.","exploitability":"Exploitation is relatively easy if the REAL_IP_HEADER is not set, requiring only control over the client-controlled header.","blast_radius":"If exploited, this could lead to unauthorized access to mail server resources, compromising user accounts and emails.","remediation":"Ensure that REAL_IP_HEADER is properly configured in the Mailu deployment.","tags":["auth-bypass","header-manipulation","mail-server","nginx"],"model":"qwen2.5:7b-instruct","analyzedAt":"2026-09-22T06:02:24.691Z"}}