CVE-2026-88004 is a high severity trailer header bypass flaw in Traefik, scored 7.4. Traefik 3.7.13. Check your installed version against the affected list below, then patch or restrict access until you can. The record does not flag it as exploited.
What's affected
- Traefik from 3.2.0 until 3.7.13.
Severity in the record: High (7.4), vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N. Weakness: CWE-436, CWE-807.
Fix: Traefik 3.7.13.
How to check if you're exposed
- Run
traefik version, or for containersdocker image ls traefik. - On Kubernetes:
kubectl describe pods -A | grep -i 'image:' | grep traefik. - Check whether your backends merge HTTP trailers into headers, and whether retry or buffering middleware is enabled.
Run these on every host, image and build that could carry the component. Dependency files in repositories and base images in registries are easy to miss.
What to do now
- Confirm the version of every affected system using the checks above.
- Read the vendor advisory linked in Sources and note the fixed version for your release line.
- Schedule the update, starting with systems that face untrusted networks or hold the most sensitive data.
- In the meantime: treat any identity header your backend trusts as a place to test after upgrade.
- Record the change, then recheck the version to confirm it took effect.
Why it matters
Traefik's entrypoint defenses (aliasHeadersStrategy, underscoreHeadersStrategy and forwardedHeaders) inspect request headers but not trailers. A client can put a protected header name in an HTTP/1.1 chunked trailer or an HTTP/2 trailer. When retry or buffering middleware reads the body first, the trailer value can reach a backend that merges trailers into the header namespace. The result is a bypass of the documented delete or reject behavior, which can spoof identity or forwarded routing data. The weakness classes are CWE-436 and CWE-807.
The record's KEV flag is false, so this post makes no claim that the flaw is exploited in the wild. That can change, so recheck the CISA catalog from time to time.
Libraries like this often arrive as transitive dependencies, so the version in your lockfile may not be one you chose. Safeguard's free in-browser dependency scan can show whether the package is in a project, and reachability analysis helps separate code paths that call the weak function from those that never do.
The vector string in the record is a compact summary of how the flaw is reached and what it costs. AV is the attack vector (network, adjacent or local), PR is the privilege the attacker needs, and the C, I and A letters give the impact on confidentiality, integrity and availability. Read it against your own network layout rather than relying on the score alone.
After you patch
Patching is not the end of the job. Recheck the version on each system, because an upgrade that failed or rolled back looks the same as a success until someone looks. Keep the advisory link with your change record so the next reviewer can see why the update happened.
If you cannot patch soon, write down the reason, the compensating control you chose and a date to revisit. Exceptions without a date tend to become permanent.
Quick check
Does every Traefik install face this?
No. It needs a backend that merges trailers into headers and middleware that reads the body early, per the record.
Sources
-
Traefik: GHSA-v67p-phpq-fc8x
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Safeguard Gold: CVE-2026-88004
Last reviewed: 18 October 2026.
