Proxy Authentication Vulnerability in Mailu Mail Server by Mailu
CVE-2026-85751

9.8CRITICAL

Key Information:

Vendor

Mailu

Status
Mailu
Helm-charts
Vendor
CVE Published:
21 September 2026

What is CVE-2026-85751?

A vulnerability exists in Mailu's mail server affecting deployments with PROXY_AUTH_WHITELIST configured, but the REAL_IP_HEADER unset. This configuration allows unauthenticated attackers to exploit client-controlled X-Forwarded-By headers, spoofing trusted proxy identities and bypassing authentication mechanisms. The issue is resolved in Mailu versions 2024.06.55 and helm-charts 2.7.3, ensuring secure handling of proxy authentication.

Affected Version(s)

helm-charts < 2.7.3

Mailu >= 2.0.0, < 2024.06.55

References

https://github.com/Mailu/Mailu/security/advisories/GHSA-r...
x_refsource_CONFIRM
https://github.com/Mailu/Mailu/pull/4070
x_refsource_MISC
https://github.com/Mailu/Mailu/pull/4071
x_refsource_MISC

CVSS V3.1

Score:
9.8
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.