CVE-2026-85751 (GCVE-0-2026-85751)

Vulnerability from cvelistv5 – Published: 2026-09-21 15:39 – Updated: 2026-09-21 17:56
VLAI
Title
Mailu: Authentication bypass in header-based proxy authentication via spoofable `X-Forwarded-By` trust
Summary
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.
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: yes Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-21 17:56 UTC
CWE
  • CWE-290 - Authentication Bypass by Spoofing
  • CWE-807 - Reliance on Untrusted Inputs in a Security Decision
Assigner
GitHub_M CNA under the mitre root
CNA scorecard C 72/100 over 7771 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Mailu Mailu Affected: >= 2.0.0, < 2024.06.55
guessed Create a notification for this product.
Mailu helm-charts Affected: < 2.7.3
guessed Create a notification for this product.
Show details on NVD website
To clipboard 

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