Is CVE-2026-85751 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-85751 being exploited in the wild.

How severe is CVE-2026-85751?

Critical severity, with a CVSS score of 9.8, published 21 September 2026.

Which products and versions are affected?

Mailu Helm-Charts prior to 2.7.3; Mailu 2.0 to 2024.06.54.

Is there a fix for CVE-2026-85751?

A patch was published on 2024-06-55: Fixed in Mailu 2024.06.55 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-85751 attacked?

It is attacked over the network.

Am I affected by CVE-2026-85751?

Check whether you run Mailu Helm-Charts or Mailu at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-85751: Mailu mail server authentication bypass via header spoofing

CVE-2026-85751 · Severity: critical · CVSS 9.8 · Published 2026-09-21

Mailu is a mail server distributed as Docker images. When proxy authentication is enabled but misconfigured, attackers can spoof the X-Forwarded-By header to bypass authentication and gain unauthorized access to the mail server. This allows unauthenticated users to access email accounts and data without valid credentials.

Technologies: Mailu. Vendors: Mailu.

Quick answers

Is CVE-2026-85751 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-85751 being exploited in the wild.
How severe is CVE-2026-85751?: Critical severity, with a CVSS score of 9.8, published 21 September 2026.
Which products and versions are affected?: Mailu Helm-Charts prior to 2.7.3; Mailu 2.0 to 2024.06.54.
Is there a fix for CVE-2026-85751?: A patch was published on 2024-06-55: Fixed in Mailu 2024.06.55 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-85751 attacked?: It is attacked over the network.
Am I affected by CVE-2026-85751?: Check whether you run Mailu Helm-Charts or Mailu at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability exists in the nginx proxy configuration when PROXY_AUTH_WHITELIST is set but REAL_IP_HEADER is unset. The proxy_hide_header directive hides the X-Forwarded-By header in upstream responses but fails to overwrite or validate incoming client-controlled requests, allowing header spoofing. An unauthenticated remote attacker can send a crafted X-Forwarded-By header to impersonate a trusted proxy and bypass authentication.

Affected products

Mailu Mailu 2.0 to 2024.06.54
Mailu helm-charts prior to 2.7.3

Timeline

2026-09-21: disclosed
2024-06-55: patched: Fixed in Mailu 2024.06.55
2024-07: patched: Fixed in helm-charts 2.7.3

References

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