CVSS 4.0
5.1 mediumCVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:NCVE-2026-33433
Medium (5.1) in traefik traefik. EPSS 0.5% chance of exploitation in the next 30 days. Fixed in github.com/traefik/traefik/v2 2.11.42.
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.
Severity
CVSS 3.1
8.8 highCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H- EPSS
- 0.5% chance of exploitation in the next 30 days; higher than 41% of CVEs (scores of 2026-10-31)
- CWE
- CWE-290
- Published
- Modified
- Record from
- the NVD, synced
Affected
- traefik:traefik
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-qr99-7898-vr7c | Go | github.com/traefik/traefik/v2 | <2.11.42 | 2.11.42 |
| GHSA-qr99-7898-vr7c | Go | github.com/traefik/traefik/v3 | >=3.0.0-beta1 <3.6.12 | 3.6.12 |
| GHSA-qr99-7898-vr7c | Go | github.com/traefik/traefik/v3 | >=3.7.0-ea.1 <3.7.0-ea.3 | 3.7.0-ea.3 |
| GO-2026-4893 | Go | github.com/traefik/traefik | all versions | no fix published |
| GO-2026-4893 | Go | github.com/traefik/traefik/v2 | <2.11.42 | 2.11.42 |
| GO-2026-4893 | Go | github.com/traefik/traefik/v3 | >=3.0.0-beta1 <3.6.12 >=3.7.0-ea.1 <3.7.0-ea.3 | 3.6.12, 3.7.0-ea.3 |