CVE-2026-85751
Mailu: Authentication bypass in header-based proxy authentication via spoofable `X-Forwarded-By` trust
- 9.8CriticalCVSS base score
- 0.56%Exploitation in 30 daysEPSS · top 53% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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.
Timeline
ID reserved
By GitHub_M
- 17 days later
· 17 days later
Published
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.1 | Critical9.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| NVDNVD · Deferred | 3.1 | Critical9.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
- EPSS (exploitation in 30 days)
- 0.56% · top 53% of all CVEs (11 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: yes · Technical impact: total
The list uses the assigner's score when there is one, then CISA's, then NVD's: Critical 9.8.
Affected products
- affected >= 2.0.0, < 2024.06.55
- affected < 2.7.3
References
6
- https://github.com/Mailu/Mailu/security/advisories/GHSA-rfhj-4wcq-74xg (opens in a new tab)x_refsource_CONFIRM
- https://github.com/Mailu/Mailu/pull/4070 (opens in a new tab)x_refsource_MISC
- https://github.com/Mailu/Mailu/pull/4071 (opens in a new tab)x_refsource_MISC
- https://github.com/Mailu/Mailu/commit/dffa97cbd889ab208246372ce9c86e99abb27ae9 (opens in a new tab)x_refsource_MISC
- https://github.com/Mailu/Mailu/commit/ff4003d045753013470945336448dbd790cac778 (opens in a new tab)x_refsource_MISC
- https://github.com/Mailu/Mailu/releases/tag/2024.06.55 (opens in a new tab)x_refsource_MISC
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-83975 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-85751)Record last updated .