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Review reviewHigh

CVE-2026-39858

traefik traefik, Red Hat OpenShift Dev Spaces 3.28

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 for...

CVSS
7.8
EPSS
0.48%
38.8% percentile
CISA KEV
Not listed
Published
2026.05.01
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability0.48%
Technical severityCVSS 7.8

Vulnerability overview

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 for...

Affected product and versions

Product
traefik traefik, Red Hat OpenShift Dev Spaces 3.28
Affected versions
>= < 2.11.43, >= >= 3.0.0-beta1, < 3.6.14, >= >= 3.7.0-ea.1, < 3.7.0-rc.2, < 2.11.43, >= 3.0.0 < 3.6.14, 3.7.0
Fixed versions
2.11.43, 3.6.14

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that traefik traefik, Red Hat OpenShift Dev Spaces 3.28 and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS 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/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
CWE
CWE-289, CWE-290, CWE-306
CVE-2026-39858 — traefik traefik, Red Hat OpenShift Dev Spaces 3.28 | SECUFOCUS NOW