Vulnerability in Mailu Helm-Charts
CVE-2026-85751
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.006 (46.5th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 47th percentile — 46.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000
Affected products
- Mailu Helm-Charts — versions < 2.7.3
- Mailu — versions >= 2.0.0, < 2024.06.55
Weakness classification (CWE)
References
- github.com/Mailu/Mailu/security/advisories/GHSA-rfhj-4wcq-74xg
- github.com/Mailu/Mailu/pull/4070
- github.com/Mailu/Mailu/pull/4071
- github.com/Mailu/Mailu/commit/dffa97cbd889ab208246372ce9c86e99abb27ae9
- github.com/Mailu/Mailu/commit/ff4003d045753013470945336448dbd790cac778
- github.com/Mailu/Mailu/releases/tag/2024.06.55
Frequently asked questions
- What is CVE-2026-85751?
- CVE-2026-85751 is a critical-severity vulnerability in Mailu Helm-Charts, classified under Authentication Bypass by Spoofing. CVSS score: 9.8/10. Published 2026-09-21.
- How severe is CVE-2026-85751?
- Critical severity. CVSS v3 base score is 9.8 out of 10.