---
id: CVE-2026-85751
title: Mailu is a mail server distributed as a set of Docker images
summary: >-
  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-F…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-290
  - CWE-807
vendor: Mailu
product: Mailu
affected:
  - 'Mailu >= 2.0.0, < 2024.06.55'
  - helm-charts < 2.7.3
published: '2026-09-21'
updated: '2026-09-21'
sourceUpdated: '2026-09-21T18:17:11.697'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-85751'
references:
  - url: >-
      https://github.com/Mailu/Mailu/commit/dffa97cbd889ab208246372ce9c86e99abb27ae9
    label: security-advisories@github.com
  - url: >-
      https://github.com/Mailu/Mailu/commit/ff4003d045753013470945336448dbd790cac778
    label: security-advisories@github.com
  - url: 'https://github.com/Mailu/Mailu/pull/4070'
    label: security-advisories@github.com
  - url: 'https://github.com/Mailu/Mailu/pull/4071'
    label: security-advisories@github.com
  - url: 'https://github.com/Mailu/Mailu/releases/tag/2024.06.55'
    label: security-advisories@github.com
  - url: 'https://github.com/Mailu/Mailu/security/advisories/GHSA-rfhj-4wcq-74xg'
    label: security-advisories@github.com
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-09-21T17:56:04.999383Z'
ingestedAt: '2026-09-21T16:11:47.447Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.