Vulnerability in Traefik
CVE-2026-33433
Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.42, 3.6.11, and 3.7.0-ea.3, when `headerField` is configured with a non-canonical HTTP header name (e.g., `x-auth-user` instead of `X-Auth-User`), an authenticated attacker can inject their own canonical version of that header to impersonate any identity to the backend. The backend receives two header entries — the attacker-injected canonical one is read first, overriding Traefik's non-canonical write. Versions 2.11.42, 3.6.11, and 3.7.0-ea.3 patch the issue.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.006 (44.8th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 45th percentile — 44.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.006 · change: +0.001
Affected products
- Traefik — versions >= 3.7.0-ea.1, < 3.7.0-ea.3, 3.7.0, >= 3.0.0-beta1, < 3.6.11
Weakness classification (CWE)
References
- github.com/traefik/traefik/security/advisories/GHSA-qr99-7898-vr7c (Exploit, Patch, Vendor Advisory)
- github.com/traefik/traefik/releases/tag/v2.11.42 (Product, Release Notes)
- github.com/traefik/traefik/releases/tag/v3.6.11 (Product, Release Notes)
- github.com/traefik/traefik/releases/tag/v3.7.0-ea.3 (Product, Release Notes)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Frequently asked questions
- What is CVE-2026-33433?
- CVE-2026-33433 is a high-severity vulnerability in Traefik, classified under Authentication Bypass by Spoofing. CVSS score: 8.8/10. Published 2026-03-27.
- How severe is CVE-2026-33433?
- High severity. CVSS v3 base score is 8.8 out of 10.