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 ↗

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

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

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