CVE-2026-88879

[CVE catalog]

Severity

Critical · CVSS 9.6CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

Published

Sep 10, 2026, 1:05:30 PM UTC

Updated

Sep 10, 2026, 2:17:16 PM UTC

Source

[NVD] · [CVE record]

EPSS

0.29% · Oct 25, 2026

A flaw was found in Traefik, an HTTP reverse proxy and load balancer. Due to a discrepancy in how Traefik and certain backend applications process HTTP header names, a remote attacker can smuggle specially crafted headers. This allows the attacker to bypass identity assertions made by Traefik, leading to identity spoofing and potentially gaining unauthorized access or elevated privileges within the backend application. github.com/traefik/traefik: Traefik: Identity spoofing via HTTP header alias A flaw was found in Traefik's header canonicalization logic, where header names are canonicalized only on dashes. A remote authenticated client can supply dot-form header aliases (e.g., X.Auth.User alongside X-Auth-User) to bypass Traefik middleware assertions. When proxied to backends that collapse non-alphanumeric characters into singular variables (e.g., CGI, WSGI, PHP, NGINX), the backend resolves the attacker-controlled header value over Traefik's asserted identity. This leads to privilege escalation or identity spoofing within the downstream application context. 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.