Authentication Bypass by Spoofing in Traefik - CVE-2026-33433
Published: May 5, 2026
Vulnerability identifier: #VU129671
CSH Severity: Low
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear
CVE-ID: CVE-2026-33433
CWE-ID: CWE-290
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Containous
Affected software:
Traefik
Traefik
Detailed vulnerability description
The vulnerability allows a remote user to spoof identities to backend services.
The vulnerability exists due to authentication bypass by spoofing in the BasicAuth and DigestAuth authentication middlewares when processing requests with a configured non-canonical headerField header name. A remote privileged user can inject a canonical version of the configured header to spoof identities to backend services.
Exploitation requires headerField to be configured with a non-canonical HTTP header name, and backend services to trust that header for authorization decisions.
How to mitigate CVE-2026-33433
Install security update from vendor's website.