CVE-2026-88004
Description
A flaw was found in Traefik, an open-source HTTP reverse proxy and load balancer. Its entrypoint defenses, designed to sanitize header names, failed to inspect request trailers. This allowed an unauthenticated client to submit malicious header names within HTTP/1.1 chunked or HTTP/2 trailers. Consequently, these unsanitized trailer values could reach backend systems, bypassing security controls and potentially leading to identity spoofing or manipulation of routing data.
Statement
A flaw was found in Traefik's request sanitization mechanism. When entrypoint defenses (aliasHeadersStrategy, underscoreHeadersStrategy, forwardedHeaders) inspect request headers, they omit checking HTTP/1.1 chunked or HTTP/2 trailers. An unauthenticated remote attacker can submit restricted header names within trailers. When buffering or retry middleware processes the payload before proxying, these trailer values pass through to backend applications that merge trailers into header namespaces. Under standard Red Hat container execution controls, this allows attackers to bypass configured proxy header deletions, leading to HTTP request smuggling, header spoofing, or unauthorized routing context manipulation.
Mitigation
Configure backend application servers to ignore HTTP request trailers, or disable HTTP/2 and chunked request buffering/retry middleware on Traefik entrypoints handling untrusted header-based authorization routing.
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 | 6.8 | 7.4 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | High | High | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Changed | Unchanged | N/A |
| Confidentiality | None | High | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N
NVD: CVSS:3.1/AV:N/AC:H/PR:N/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).
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