CVE-2026-85751

9.8 CRITICALpublic exploit available

Published 2026-09-21 · Updated 2026-09-21

AI risk analysis

Summary: The flaw allows an unauthenticated attacker to spoof trusted proxy identity and bypass authentication by manipulating the X-Forwarded-By header.
Exploitability: Exploitation is relatively easy if the REAL_IP_HEADER is not set, requiring only control over the client-controlled header.
Blast radius: If exploited, this could lead to unauthorized access to mail server resources, compromising user accounts and emails.
Prioritized remediation: Ensure that REAL_IP_HEADER is properly configured in the Mailu deployment.

auth-bypassheader-manipulationmail-servernginx

Analysis generated locally by qwen2.5:7b-instruct (no data left the box). AI-assisted — verify against primary sources before acting.

NVD 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.

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Weaknesses

CWE-290, CWE-807

Public exploit & PoC references

All references

Source data: NVD (nvd.nist.gov), public domain. Exploit-DB.ai adds local AI analysis for defensive use only.

Related CVEs

Related by shared AI tags and CWE weakness class. Browse the full archive.