Read the docs
TI-2026-28739 Aliases CVE-2026-39858GHSA-5m6w-wvh7-57vm

Traefik: Forwarded alias spoofing top pre-auth decision bypass

Priority MEDIUM 41CWE-290Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
None
Impact type
Security bypass
Confidentiality · integrity · availability
None · None · None
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-290.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00479 41st percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed traefik (traefik): 2.11.43, 3.6.14, 3.7.0-rc.2github.com/traefik/traefik/v3 (Go): 3.7.0-rc.2, 3.6.14+1 more productRed Hat: 1 advisory

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
traefiktraefikbefore 2.11.43; 3.0.0-beta1 to before 3.6.14; 3.7.0-ea.1 to before 3.7.0-rc.22.11.43, 3.6.14, 3.7.0-rc.2Patch availableCNA
—github.com/traefik/traefik/v3 (Go)3.7.0-ea.1 to before 3.7.0-rc.23.7.0-rc.2Patch availableGHSA-5m6w-wvh7-57vm
—github.com/traefik/traefik/v3 (Go)3.0.0-beta1 to before 3.6.143.6.14Patch availableGHSA-5m6w-wvh7-57vm
—github.com/traefik/traefik/v2 (Go)before 2.11.432.11.43Patch availableGHSA-5m6w-wvh7-57vm
—github.com/traefik/traefik (Go)up to 1.7.34—No fix listedGHSA-5m6w-wvh7-57vm
  • traefik Vendortraefik Affected before 2.11.43; 3.0.0-beta1 to before 3.6.14; 3.7.0-ea.1 to before 3.7.0-rc.2 Fixed in 2.11.43, 3.6.14, 3.7.0-rc.2 Patch available CNA
  • github.com/traefik/traefik/v3 (Go) Vendor— Affected 3.7.0-ea.1 to before 3.7.0-rc.2 Fixed in 3.7.0-rc.2 Patch available GHSA-5m6w-wvh7-57vm
  • github.com/traefik/traefik/v3 (Go) Vendor— Affected 3.0.0-beta1 to before 3.6.14 Fixed in 3.6.14 Patch available GHSA-5m6w-wvh7-57vm
  • github.com/traefik/traefik/v2 (Go) Vendor— Affected before 2.11.43 Fixed in 2.11.43 Patch available GHSA-5m6w-wvh7-57vm
  • github.com/traefik/traefik (Go) Vendor— Affected up to 1.7.34 Fixed in — No fix listed GHSA-5m6w-wvh7-57vm

CPE configurations NVD · 5

CPEVersionsRoleVendor
cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*before 2.11.43; 3.0.0 to before 3.6.14Vulnerabletraefik
cpe:2.3:a:traefik:traefik:3.7.0:ea1:*:*:*:*:*:*3.7.0 ea1Vulnerabletraefik
cpe:2.3:a:traefik:traefik:3.7.0:ea2:*:*:*:*:*:*3.7.0 ea2Vulnerabletraefik
cpe:2.3:a:traefik:traefik:3.7.0:ea3:*:*:*:*:*:*3.7.0 ea3Vulnerabletraefik
cpe:2.3:a:traefik:traefik:3.7.0:rc1:*:*:*:*:*:*3.7.0 rc1Vulnerabletraefik
  • cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:* Versions before 2.11.43; 3.0.0 to before 3.6.14 Vulnerable ·traefik
  • cpe:2.3:a:traefik:traefik:3.7.0:ea1:*:*:*:*:*:* Versions 3.7.0 ea1 Vulnerable ·traefik
  • cpe:2.3:a:traefik:traefik:3.7.0:ea2:*:*:*:*:*:* Versions 3.7.0 ea2 Vulnerable ·traefik
  • cpe:2.3:a:traefik:traefik:3.7.0:ea3:*:*:*:*:*:* Versions 3.7.0 ea3 Vulnerable ·traefik
  • cpe:2.3:a:traefik:traefik:3.7.0:rc1:*:*:*:*:*:* Versions 3.7.0 rc1 Vulnerable ·traefik

Remediation

  • Fix · CNA traefik (traefik) Fixed in 2.11.43, 3.6.14, 3.7.0-rc.2
  • Fix · GHSA-5m6w-wvh7-57vm github.com/traefik/traefik/v3 (Go) Fixed in 3.7.0-rc.2 Advisory →
  • Fix · GHSA-5m6w-wvh7-57vm github.com/traefik/traefik/v3 (Go) Fixed in 3.6.14 Advisory →
  • Fix · GHSA-5m6w-wvh7-57vm github.com/traefik/traefik/v2 (Go) Fixed in 2.11.43 Advisory →

Red Hat 1 advisory

  • RHSA-2026:21772 Released 2026-05-28 · Red Hat rating Important
    Red Hat OpenShift Dev Spaces 3.28.0 Release.
    • Red Hat OpenShift Dev Spaces 3.28 registry.redhat.io/devspaces/code-rhel9, registry.redhat.io/devspaces/dashboard-rhel9, registry.redhat.io/devspaces/openvsx-rhel9 +3

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat OpenShift Dev Spaces 3.28Fixed RHSA-2026:21772
Not affected: 1 product
  • Red Hat OpenShift Dev Spaces 3.28

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-39858
  2. 2026-10-03 Alias added: GHSA-5m6w-wvh7-57vm

References

Exploit 1

Advisory 1

Other 4

  • TI-2023-23979 The HTTP/2 protocol allows a denial of service (server resource consumption) because… KEVCVSS 3.1HIGH 7.5
  • TI-2023-25774 Uncontrolled Resource Consumption in Traefik CVSS 3.1HIGH 7.5
  • TI-2025-40914 Traefik doesn't Prevent Path Normalization Bypass in Router + Middleware Rules CVSS 4.0MEDIUM 6.9
  • TI-2022-07529 Authorization header displayed in the debug logs CVSS 3.1MEDIUM 6.5
  • TI-2024-30459 HTTP client can remove the X-Forwarded headers in Traefik CVSS 3.1CRITICAL 9.8
  • TI-2026-60261 Traefik v3.7.0 Authentication Bypass via from-to-www-redirect CVSS 4.0CRITICAL 9.3
See all 83 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences