CVE-2026-88011

[CVE catalog]

Severity

Critical · CVSS 9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Published

Sep 10, 2026, 3:31:55 PM UTC

Updated

Sep 10, 2026, 4:18:07 PM UTC

Source

[NVD] · [CVE record]

EPSS

0.42% · Oct 25, 2026

A flaw was found in Traefik, an open-source HTTP reverse proxy and load balancer. A remote attacker can exploit this vulnerability by sending a specially crafted dot-form header, such as X.Authenticated.User. Due to a discrepancy in how Go and certain backend systems (like CGI, WSGI, PHP, and NGINX) interpret these headers, the backend may consume the client's supplied value instead of the identity asserted by Traefik. This allows for identity spoofing for any header managed by Traefik, potentially leading to unauthorized access or actions. github.com/traefik/traefik: Traefik: Identity spoofing via dot-form header alias A flaw in Traefik allows remote attackers to spoof identity and authorization headers passed to backend services. Traefik canonicalizes headers containing dashes but ignores dot-form aliases (e.g., X.Authenticated.User), allowing them to bypass ForwardAuth replacement middleware. When requests reach normalization-prone backends (such as CGI, WSGI, PHP, or NGINX), these platforms collapse dot-form aliases and canonical headers into identical environment variables, causing the backend to consume the attacker-controlled value instead of Traefik's asserted identity. The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.