Mailu: Authentication bypass in header-based proxy authentication via spoofable `X-Forwarded-By` trust
Published Sep 21, 2026
9.8
CRITICALCVSS 3.1
EPSS 0.56%
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.
Affected products
-
- Version >= 2.0.0, < 2024.06.55StatusaffectedConstraints-
- Version
-
- Version < 2.7.3StatusaffectedConstraints-
- Version
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Mailu | Mailu | n/a |
| ||||||
| Mailu | Helm-Charts | n/a |
|
No data.
No data.
No Red Hat product state for this CVE.
No package ranges for this CVE.
Remediation
No remediation recorded yet.
Metrics
No CVSS v4.0 score for this CVE.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
No CVSS v3.0 score for this CVE.
No CVSS v2.0 score for this CVE.
This CVE is not in the KEV list.
CISA SSVC (Vulnrichment)
Stakeholder-Specific Vulnerability Categorization from CISA ADP.
Exploitation
NoneAutomatable
YesTechnical Impact
TotalDecision
n/aAssessed Sep 21, 2026 · SSVC 2.0.3
Estimated probability of exploitation in the wild in the next 30 days (FIRST EPSS). As of Oct 1, 2026.
Score over time
Sep–Oct 2026- EPSS v5
Percentile over time
- EPSS v5
Table of values (2 key points)
Flat stretches are collapsed; showing up to 120 newest points.
| Date | Score | Percentile | Model |
|---|---|---|---|
| Oct 1, 2026 | 0.56% (0.00557) | 44.43th | v5 (v2026.06.15) |
| Sep 22, 2026 | 0.56% (0.00557) | 45.28th | v5 (v2026.06.15) |
References (6)
- https://github.com/Mailu/Mailu/commit/dffa97cbd889ab208246372ce9c86e99abb27ae9 x_refsource_MISC
- https://github.com/Mailu/Mailu/commit/ff4003d045753013470945336448dbd790cac778 x_refsource_MISC
- https://github.com/Mailu/Mailu/pull/4070 x_refsource_MISC
- https://github.com/Mailu/Mailu/pull/4071 x_refsource_MISC
- https://github.com/Mailu/Mailu/releases/tag/2024.06.55 x_refsource_MISC
- https://github.com/Mailu/Mailu/security/advisories/GHSA-rfhj-4wcq-74xg x_refsource_CONFIRM
| Link | Providers | Tags |
|---|---|---|
| https://github.com/Mailu/Mailu/commit/dffa97cbd889ab208246372ce9c86e99abb27ae9 | x_refsource_MISC | |
| https://github.com/Mailu/Mailu/commit/ff4003d045753013470945336448dbd790cac778 | x_refsource_MISC | |
| https://github.com/Mailu/Mailu/pull/4070 | x_refsource_MISC | |
| https://github.com/Mailu/Mailu/pull/4071 | x_refsource_MISC | |
| https://github.com/Mailu/Mailu/releases/tag/2024.06.55 | x_refsource_MISC | |
| https://github.com/Mailu/Mailu/security/advisories/GHSA-rfhj-4wcq-74xg | x_refsource_CONFIRM |
Change history (0)
No recorded changes yet.