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CVE-2026-85751— Mailu: Authentication bypass in header-based proxy authentication via spoofable `X-Forwarded-By` trust

Quick assessment

Affected
Mailu Mailu
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

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

CVSS 9.8 · Critical EPSS 0.56% · P45

Affected Version Matrix 2

VendorProduct Version RangeStatus
Mailu helm-charts < 2.7.3 affected
Mailu Mailu >= 2.0.0, < 2024.06.55 affected
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I. Basic Information for CVE-2026-85751

Vulnerability Information

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Vulnerability Title
Mailu: Authentication bypass in header-based proxy authentication via spoofable `X-Forwarded-By` trust
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
使用欺骗进行的认证绕过
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Mailu Mailu >= 2.0.0, < 2024.06.55 -
Mailu helm-charts < 2.7.3 -

II. Public POCs for CVE-2026-85751

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III. Intelligence Information for CVE-2026-85751

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Patches & Fixes for CVE-2026-85751 (4)

Other References for CVE-2026-85751 (2)

IV. Related Vulnerabilities

Same product: Mailu
Same vendor: Mailu
Same weakness: CWE-290

V. Comments for CVE-2026-85751

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