Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.43, 3.6.14, and 3.7.0-rc.2, there is a high severity authentication bypass vulnerability in Traefik's ForwardAuth and snippet-based authentication middleware. Traefik's forwarded-header sanitization logic targets only canonical header names (e.g., X-Forwarded-Proto) and does not strip or normalize alias variants that use underscores instead of dashes (e.g., X_Forwarded_Proto). These unsanitized alias headers are forwarded intact to the authentication backend. When the backend normalizes underscore and dash header forms equivalently, an attacker can inject spoofed trust context — such as a trusted scheme or host — through the alias headers and bypass authentication on protected routes without valid credentials. This issue has been patched in versions 2.11.43, 3.6.14, and 3.7.0-rc.2.
History

Mon, 04 May 2026 17:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 01 May 2026 17:45:00 +0000

Type Values Removed Values Added
CPEs cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*
cpe:2.3:a:traefik:traefik:3.7.0:ea1:*:*:*:*:*:*
cpe:2.3:a:traefik:traefik:3.7.0:ea2:*:*:*:*:*:*
cpe:2.3:a:traefik:traefik:3.7.0:ea3:*:*:*:*:*:*
cpe:2.3:a:traefik:traefik:3.7.0:rc1:*:*:*:*:*:*
Metrics cvssV3_1

{'score': 10.0, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N'}


Thu, 30 Apr 2026 21:45:00 +0000

Type Values Removed Values Added
First Time appeared Traefik
Traefik traefik
Vendors & Products Traefik
Traefik traefik

Thu, 30 Apr 2026 20:45:00 +0000

Type Values Removed Values Added
Description Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.43, 3.6.14, and 3.7.0-rc.2, there is a high severity authentication bypass vulnerability in Traefik's ForwardAuth and snippet-based authentication middleware. Traefik's forwarded-header sanitization logic targets only canonical header names (e.g., X-Forwarded-Proto) and does not strip or normalize alias variants that use underscores instead of dashes (e.g., X_Forwarded_Proto). These unsanitized alias headers are forwarded intact to the authentication backend. When the backend normalizes underscore and dash header forms equivalently, an attacker can inject spoofed trust context — such as a trusted scheme or host — through the alias headers and bypass authentication on protected routes without valid credentials. This issue has been patched in versions 2.11.43, 3.6.14, and 3.7.0-rc.2.
Title Traefik: Forwarded alias spoofing top pre-auth decision bypass
Weaknesses CWE-290
CWE-306
References
Metrics cvssV4_0

{'score': 7.8, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published: 2026-04-30T20:26:26.300Z

Updated: 2026-05-04T16:58:14.458Z

Reserved: 2026-04-07T19:13:20.379Z

Link: CVE-2026-39858

cve-icon Vulnrichment

Updated: 2026-05-04T16:58:09.098Z

cve-icon NVD

Status : Analyzed

Published: 2026-04-30T21:16:32.313

Modified: 2026-05-01T17:44:36.067

Link: CVE-2026-39858

cve-icon Redhat

No data.