---
title: "CVE-2026-85751: Mailu - Authentication Bypass"
description: "Mailu 2.0 to 2024.06.55 and helm-charts prior to 2.7.3 contain an authentication bypass caused by trusting client-controlled X-Forwarded-By header when REAL_IP_HEADER is unset, letting unauthenticated remote attackers bypass proxy authentication, exploit requires PROXY_AUTH_WHITELIST configured and REAL_IP_HEADER unset."
url: https://panop.io/threat-heartbeat/CVE-2026-85751/
---

# CVE-2026-85751 Mailu - Authentication Bypass

Mailu 2.0 to 2024.06.55 and helm-charts prior to 2.7.3 contain an authentication bypass caused by trusting client-controlled X-Forwarded-By header when REAL\_IP\_HEADER is unset, letting unauthenticated remote attackers bypass proxy authentication, exploit requires PROXY\_AUTH\_WHITELIST configured and REAL\_IP\_HEADER unset.

CVSS base score 9.8 /10

Critical

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.56% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-85751)

## Details

Type

Authentication Bypass

Impact

Broken Authentication

CVSS vector

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

Published

21 September 2026

Updated

15 October 2026

Weakness

[CWE-290](https://cwe.mitre.org/data/definitions/290.html)

## Vendor fix

Update to Mailu 2024.06.55 and Mailu helm-charts 2.7.3 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-85751](https://nvd.nist.gov/vuln/detail/CVE-2026-85751)
- [https://github.com/Mailu/Mailu/commit/dffa97cbd889ab208246372ce9c86e99abb27ae9](https://github.com/Mailu/Mailu/commit/dffa97cbd889ab208246372ce9c86e99abb27ae9)
- [https://github.com/Mailu/Mailu/commit/ff4003d045753013470945336448dbd790cac778](https://github.com/Mailu/Mailu/commit/ff4003d045753013470945336448dbd790cac778)
- [https://github.com/Mailu/Mailu/pull/4070](https://github.com/Mailu/Mailu/pull/4070)
- [https://github.com/Mailu/Mailu/pull/4071](https://github.com/Mailu/Mailu/pull/4071)
- [https://github.com/Mailu/Mailu/releases/tag/2024.06.55](https://github.com/Mailu/Mailu/releases/tag/2024.06.55)
- [https://github.com/Mailu/Mailu/security/advisories/GHSA-rfhj-4wcq-74xg](https://github.com/Mailu/Mailu/security/advisories/GHSA-rfhj-4wcq-74xg)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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