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CVE-2026-85751

9.8 · CRITICAL

Mailu is a mail server distributed as a set of Docker images.

Published Sep 21, 2026CWE-290EPSS 0.56%

Overview

CVE-2026-85751 is a critical-severity vulnerability. It was published on September 21, 2026 and has a CVSS 3.1 base score of 9.8 (CRITICAL).

This vulnerability has a CVSS 3.1 base score of 9.8, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/Mailu/Mailu/commit/dffa97cbd889ab208246372ce9c86e99abb27ae9GitHubgithub.com/Mailu/Mailu/commit/ff4003d045753013470945336448dbd790cac778GitHubgithub.com/Mailu/Mailu/pull/4070GitHubgithub.com/Mailu/Mailu/pull/4071GitHubgithub.com/Mailu/Mailu/releases/tag/2024.06.55GitHubgithub.com/Mailu/Mailu/security/advisories/GHSA-rfhj-4wcq-74xg

How CyberStrike helps

Frequently asked questions

What is CVE-2026-85751?

CVE-2026-85751 is a critical-severity vulnerability. It was published on September 21, 2026 and has a CVSS 3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2026-85751?

This vulnerability has a CVSS 3.1 base score of 9.8, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-85751?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-85751?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-85751 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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