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High, CVSS 7.0amended

Traefik entrypoint header-name sanitization bypassed via request trailers

CVE-2026-88004GHSA-v67p-phpq-fc8x

What to do

Partial vendor fix. Follow the primary source's mitigation guidance and check back for a fix.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • Go github.com/traefik/traefik/v3

    Affected
    >= 3.2.0, < 3.7.13
    Fixed in
    3.7.13

  • Go github.com/traefik/traefik/v2

    Affected
    every version
    Fixed in
    no fixed version recorded

  • Go github.com/traefik/traefik

    Affected
    every version
    Fixed in
    no fixed version recorded

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
7.0 · 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 · score source
EPSS
  • CVE-2026-88004: 0.45% estimated exploitation activity in the next 30 days; percentile 39.32 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary Traefik's entrypoint defenses against spoofed trusted header names — aliasHeadersStrategy / underscoreHeadersStrategy in delete or reject mode, and the default forwardedHeaders stripping of client-supplied X-Forwarded- — scan req.Header only and never req.Trailer. An unauthenticated client can therefore smuggle a sanitized name (an aliasing spelling such as XAuthUser, or a trusted name such as X-Forwarded-Prefix) as an HTTP/1.1 chunked trailer or an HTTP/2 trailer: reject does not return its documented 400, delete does not remove the name, and Traefik's reverse proxy forwarded the trailer to the backend — with an attacker-chosen value whenever a body-buffering middleware (the retry middleware with status codes, or the buffering middleware) reads the body before the proxy clone. Backends that merge trailers into their header namespace then act on the smuggled name. The fix stops forwarding request trailer values to the backend; the declared trailer names are still forwarded as…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 4 · amended ·

    Amended from ghsa record GHSA-v67p-phpq-fc8x

  2. Revision 3 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 2 · amended ·

    Amended from osv record GO-2026-6467

  4. Revision 1 · created ·

    Published from osv record GHSA-v67p-phpq-fc8x

Agent brief

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# Patch Next advisory brief: CVE-2026-88004

Advisory: Traefik entrypoint header-name sanitization bypassed via request trailers
IDs: CVE-2026-88004, GHSA-v67p-phpq-fc8x
Record: https://patchnext.com/advisories/cve-2026-88004 (revision 4, source checked 26 Oct 2026, 15:29 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: github.com/traefik/traefik/v3 3.7.13. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/traefik/traefik/v3: affected >= 3.2.0, < 3.7.13; fixed in 3.7.13
- Go github.com/traefik/traefik/v2: affected every version
- Go github.com/traefik/traefik: affected every version

## Suggested inspection (read-only)
- Go github.com/traefik/traefik/v3: check the installed version with your package manager.
- Go github.com/traefik/traefik/v2: check the installed version with your package manager.
- Go github.com/traefik/traefik: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/traefik/traefik/v3, github.com/traefik/traefik/v2, github.com/traefik/traefik.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-v67p-phpq-fc8x (OSV record GHSA-v67p-phpq-fc8x lists affected ranges: Go github.com/traefik/traefik/v3 >=3.2.0 <3.7.13 (fixed))
- Verified: https://osv.dev/vulnerability/GO-2026-6467 (OSV record GO-2026-6467 lists affected ranges: Go github.com/traefik/traefik >=0; Go github.com/traefik/traefik/v2 >=0; Go github.com/traefik/traefik/v3 >=3.2.0 <3.7.13 (fixed))
- Verified: https://github.com/advisories/GHSA-v67p-phpq-fc8x (GitHub-reviewed advisory GHSA-v67p-phpq-fc8x lists affected ranges: Go github.com/traefik/traefik/v3 >=3.2.0 <3.7.13)

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