CVE-2026-85751Mailu: Authentication bypass in header-based proxy authentication via spoofable `X-Forwarded-By` trust
Updated under an hour ago ()
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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.
- CVSS
- 9.8 CRITICAL (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Weakness (CWE)
- CWE-290, CWE-807
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- GitHub_M
- NVD analysis
- Deferred
- Record last updated
- Sep 21, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Mailu Mailu mailu:mailu (from the name) | from 2.0.0, < 2024.06.55 | CNA record |
Mailu helm-charts mailu:helm_charts (from the name) | before 2.7.3 | CNA record |
References
- https://github.com/Mailu/Mailu/security/advisories/GHSA-rfhj-4wcq-74xgx-refsource-confirm
- https://github.com/Mailu/Mailu/pull/4070x-refsource-misc
- https://github.com/Mailu/Mailu/pull/4071x-refsource-misc
- https://github.com/Mailu/Mailu/commit/dffa97cbd889ab208246372ce9c86e99abb27ae9x-refsource-misc
- https://github.com/Mailu/Mailu/commit/ff4003d045753013470945336448dbd790cac778x-refsource-misc
- https://github.com/Mailu/Mailu/releases/tag/2024.06.55x-refsource-misc
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.