CVE-2026-39858
Critical · 10.0CVSS
10.0
EPSS
0.6%
Published
Apr 30, 2026
CISA due date
—
The record
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.
Affected packages
| Ecosystem | Package | Introduced | Fixed |
|---|---|---|---|
| openSUSE:Tumbleweed | traefik | 0 | 3.6.15-1.1 |
| openSUSE:Tumbleweed | traefik2 | 0 | 2.11.44-1.1 |
Related vulnerabilities
- CVE-2026-48491 Traefik is an HTTP reverse proxy and load balancer. Also affects traefik
- CVE-2026-53622 Traefik is an HTTP reverse proxy and load balancer. Also affects traefik
- CVE-2026-48020 Traefik is an HTTP reverse proxy and load balancer. Also affects traefik
- CVE-2026-44774 Traefik is an HTTP reverse proxy and load balancer. Also affects traefik
- CVE-2026-41181 Traefik is an HTTP reverse proxy and load balancer. Also affects traefik
- CVE-2026-41174 Traefik is an HTTP reverse proxy and load balancer. Also affects traefik
- CVE-2026-41263 Traefik is an HTTP reverse proxy and load balancer. Also affects traefik
- CVE-2026-35051 Traefik is an HTTP reverse proxy and load balancer. Also affects traefik