CVE-2026-88011
Description
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.
Statement
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.
Mitigation
Update Traefik to 2.11.56 or 3.7.12 (or later) and explicitly configure entrypoints with 'aliasHeadersStrategy: delete' or 'aliasHeadersStrategy: reject', as the feature defaults to 'keep' for backward compatibility.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 9.1 | 8.1 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | None | Low | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Understanding the Weakness (CWE)
Integrity,Non-Repudiation,Access Control
Technical Impact: Unexpected State; Hide Activities; Bypass Protection Mechanism
An attacker could create HTTP messages to exploit a number of weaknesses including 1) the message can trick the web server to associate a URL with another URL's webpage and caching the contents of the webpage (web cache poisoning attack), 2) the message can be structured to bypass the firewall protection mechanisms and gain unauthorized access to a web application, and 3) the message can invoke a script or a page that returns client credentials (similar to a Cross Site Scripting attack).
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
