Traefik: headerField underscore-variant identity spoofing in BasicAuth / DigestAuth / ForwardAuth

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Summary

CVECVE-2026-54763
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-06 21:16:56 UTC
Updated2026-07-07 13:57:07 UTC
DescriptionTraefik is an HTTP reverse proxy and load balancer. Prior to v2.11.51, v3.6.22, and v3.7.6, Traefik's BasicAuth, DigestAuth, and ForwardAuth middlewares strip canonical-cased spoofed identity headers before writing Traefik's own value, but do not account for underscore-variant header names, which many backends normalize identically to dashed forms. An attacker able to reach a protected route can inject an underscore-variant header that survives Traefik's stripping and reaches the backend alongside, or on the unauthenticated ForwardAuth authResponseHeaders path instead of, the value Traefik intended to set, spoofing identity or authorization context. This issue is fixed in versions v2.11.51, v3.6.22, and v3.7.6.

Risk And Classification

Primary CVSS: v4.0 7.8 HIGH from [email protected]

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Problem Types: CWE-178 | CWE-290 | CWE-345 | CWE-178 CWE-178: Improper Handling of Case Sensitivity | CWE-290 CWE-290: Authentication Bypass by Spoofing | CWE-345 CWE-345: Insufficient Verification of Data Authenticity

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary7.8HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N/E:X/C...
4.0CNADECLARED7.8HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Confidentiality
None
Integrity
None
Availability
None
Sub Conf.
High
Sub Integrity
High
Sub Availability
None

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Traefik Traefik affected < 2.11.51 Not specified
CNA Traefik Traefik affected >= 3.0.0-beta1, < 3.6.22 Not specified
CNA Traefik Traefik affected >= 3.7.0-ea.1, < 3.7.6 Not specified

References

ReferenceSourceLinkTags
github.com/traefik/traefik/commit/108a5264473a2cbc8f12d6d691a3c6553cdf2c1b [email protected] github.com
github.com/traefik/traefik/pull/13262 [email protected] github.com
github.com/traefik/traefik/security/advisories/GHSA-x677-9fxg-v5c5 [email protected] github.com
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