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Medium, CVSS 5.3amended

Traefik: ForwardAuth identity spoofing via dot-form header alias

CVE-2026-88011GHSA-rf44-j88r-hh8c

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
    >= 3.0.0, < 3.7.12
    Fixed in
    3.7.12

  • Go github.com/traefik/traefik/v2

    Affected
    < 2.11.56
    Fixed in
    2.11.56

  • 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
5.3 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N · score source
EPSS
  • CVE-2026-88011: 0.42% estimated exploitation activity in the next 30 days; percentile 36.35 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
  • CVE-2026-88879: 0.29% estimated exploitation activity in the next 30 days; percentile 22.18 (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 There is a medium severity vulnerability in Traefik's handling of request headers whose name aliases another header name. Go canonicalizes header names on dashes only, so X-Auth-User, XAuthUser and X.Auth.User are three distinct headers to Traefik, while backends that derive variable names from header names (CGI, WSGI, PHP, NGINX, and others) collapse all of them into the same variable. A client can therefore smuggle an alias of a header that Traefik manages past the middleware managing it — for example a dot-form X.Authenticated.User alongside the canonical X-Authenticated-User written by the ForwardAuth middleware — and have such a backend read the client-supplied value instead of the identity Traefik asserted. Any header Traefik sets is exposed, not only ForwardAuth's. This is an incomplete-fix sibling of GHSA-x677-9fxg-v5c5, which blocked only the underscore form. The mitigation is the new aliasHeadersStrategy entry point option. It defaults to keep, which preserves the…

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

    Amended from ghsa record GHSA-rf44-j88r-hh8c

  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-2026-6455

  4. Revision 1 · created ·

    Published from osv record GHSA-rf44-j88r-hh8c

Agent brief

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# Patch Next advisory brief: CVE-2026-88011

Advisory: Traefik: ForwardAuth identity spoofing via dot-form header alias
IDs: CVE-2026-88011, GHSA-rf44-j88r-hh8c
Record: https://patchnext.com/advisories/cve-2026-88011 (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: Medium (CVSS 5.3)
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 3.7.12; github.com/traefik/traefik/v2 2.11.56. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/traefik/traefik/v3: affected >= 3.0.0, < 3.7.12; fixed in 3.7.12
- Go github.com/traefik/traefik/v2: affected < 2.11.56; fixed in 2.11.56
- 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-rf44-j88r-hh8c (OSV record GHSA-rf44-j88r-hh8c lists affected ranges: Go github.com/traefik/traefik/v2 >=0 =3.0.0 <3.7.12 (fixed))
- Verified: https://osv.dev/vulnerability/GO-2026-6455 (OSV record GO-2026-6455 lists affected ranges: Go github.com/traefik/traefik >=0; Go github.com/traefik/traefik/v2 >=0 =3.0.0 <3.7.12 (fixed))
- Verified: https://github.com/advisories/GHSA-rf44-j88r-hh8c (GitHub-reviewed advisory GHSA-rf44-j88r-hh8c lists affected ranges: Go github.com/traefik/traefik/v2 >=0 =3.0.0 <3.7.12)

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