What’s Vulnerable › Vulnerabilities

CVE-2026-88004: Traefik entrypoint header-name sanitization bypassed via request trailers

• Severity: high (CVSS 7.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-10 · updated 2026-09-14
• Weakness: CWE-436

Description

Traefik is an open source HTTP reverse proxy and load balancer. From 3.2.0 until 3.7.13, Traefik entrypoint defenses aliasHeadersStrategy, underscoreHeadersStrategy, and forwardedHeaders inspect req.Header but not req.Trailer, allowing an unauthenticated client to submit an aliasing or trusted header name in an HTTP/1.1 chunked trailer or an HTTP/2 trailer. When the retry or buffering middleware reads the body before the reverse proxy clones the request, the attacker-controlled trailer value reaches a backend that merges trailers into the header namespace, bypassing the documented delete or reject behavior and potentially spoofing identity or forwarded routing data. This issue is fixed in 3.7.13.

Affected products

• Traefik: from 3.2.0 before 3.7.13 — fixed in 3.7.13

How to fix

Upgrade to a fixed version: Traefik 3.7.13. Check the vendor advisory for mitigations.

References

• https://github.com/traefik/traefik/commit/55bbda4f65e0f9c533c870983a767a7081126db7
• https://github.com/traefik/traefik/pull/13822
• https://github.com/traefik/traefik/releases/tag/v3.7.13
• https://github.com/traefik/traefik/security/advisories/GHSA-v67p-phpq-fc8x

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