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Fencer Vulns
critical 10.0

CVE-2026-54763 json

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

published 2026-07-06 4 mo ago modified 2026-08-18 2 mo ago also GHSA-x677-9fxg-v5c5 , GO-2026-6211 , EUVD-2026-41940

cvss
10.0
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 15%
public exploits
0
none known

Summary

Traefik 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.

Patch / fix

  • go github.com/traefik/traefik/v2 2.11.51
  • go github.com/traefik/traefik/v3 3.6.22, 3.7.6
  • traefik traefik 2.11.51, 3.6.22, 3.7.6
  • govulncheck-vulndb SLES for SAP applications 16.0, SLES 16.0 0.0.20260827T195228-160000.1.1

suse advisories SUSE-SU-2026:23625-1

  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260827T195228-160000.1.1
  • traefik openSUSE Tumbleweed 3.7.7-1.1
  • traefik2 openSUSE Tumbleweed 2.11.52-1.1

opensuse advisories openSUSE-SU-2026:21761-1openSUSE-SU-2026:11251-1openSUSE-SU-2026:11243-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-54763 updated cvss 10.0

traefik: Traefik: Identity spoofing via improper header handling in authentication middlewares

  • Red Hat OpenShift Dev Spaces 3.30 devspaces/traefik-rhel9 1787756799
    fixed: vendor fix RHSA-2026:62260
  • Red Hat OpenShift Dev Spaces 3.30 devspaces/udi-rhel9 1787764814, devspaces/code-rhel9 1787762793, devspaces/server-rhel9 1787757597, devspaces/openvsx-rhel9 1787759145, devspaces/udi-base-rhel9 1787761882, devspaces/code-sshd-rhel9 1787762385, +10 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
4 mo ago

Exploit prediction

0.24% chance of exploitation in the next 30 days, higher than 15% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 7.8 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
CNA 4.0 7.8 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
NVD 3.1 10.0 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

Affected packages

ecosystem package affected fixed in
go github.com/traefik/traefik/v2
<2.11.51
2.11.51
go github.com/traefik/traefik/v3
<3.6.22
>=3.7.0, <3.7.6
3.6.22
3.7.6
go github.com/traefik/traefik
all versions
 no fix listed

Affected products

  • traefik traefik

Classification

Weakness
  • CWE-178 Improper Handling of Case Sensitivity
  • CWE-290 Authentication Bypass by Spoofing
  • CWE-345 Insufficient Verification of Data Authenticity

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.