CVE-2026-33433
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…
Does this matter?
Lower severity and a low EPSS score (0.47%). Track it; it rarely justifies an emergency change on its own.
Description
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.
- 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:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 0.47% probability · 39th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-290
- Affected
- traefik/traefik
- Source
- security-advisories@github.com
References
- https://github.com/traefik/traefik/releases/tag/v2.11.42Product, Release Notes
- https://github.com/traefik/traefik/releases/tag/v3.6.11Product, Release Notes
- https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.3Product, Release Notes
- https://github.com/traefik/traefik/security/advisories/GHSA-qr99-7898-vr7cExploit, Patch, Vendor Advisory
- https://access.redhat.com/errata/RHSA-2026:10175
- https://access.redhat.com/security/cve/CVE-2026-33433
- https://bugzilla.redhat.com/show_bug.cgi?id=2452289
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33433.json
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.