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

Source: https://junglewise.ai/threats/cve-2026-71326-traefik-basicauth-identity-spoofing-via-singleflight-key  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-06. Updated: 2026-08-06  
License: CC BY 4.0 with a link back

CVE-2026-71326 · Severity: medium · CVSS 4 · Published 2026-08-06

Traefik is a popular open-source edge router and load balancer used to manage web traffic. A flaw in its basic authentication system allows a user who already has valid credentials and access to the system's internal configuration to impersonate other users. This could allow an attacker to perform actions or access data belonging to a different account, potentially leading to unauthorized administrative changes or data exposure.

Technologies: [github.com/traefik/traefik (Go)](https://junglewise.ai/threats/technologies/github-com-traefik-traefik), [github.com/traefik/traefik/v2 (Go)](https://junglewise.ai/threats/technologies/github-com-traefik-traefik-v2), [github.com/traefik/traefik/v3 (Go)](https://junglewise.ai/threats/technologies/github-com-traefik-traefik-v3), [Traefik Labs Traefik Proxy](https://junglewise.ai/threats/technologies/traefik-proxy). Vendors: [Go](https://junglewise.ai/threats/vendors/go), [Traefik Labs](https://junglewise.ai/threats/vendors/traefik-labs).

## Quick answers

**Is CVE-2026-71326 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-71326 being exploited in the wild.

**How severe is CVE-2026-71326?** Medium severity, with a CVSS score of 4, published 6 August 2026.

**Which products and versions are affected?** github.com/traefik/traefik (Go) SEMVER:introduced=0; github.com/traefik/traefik/v2 (Go) SEMVER:introduced=0; github.com/traefik/traefik/v3 (Go) SEMVER:introduced=3.6.11,fixed=3.6.25, SEMVER:introduced=3.6.11,fixed=3.6.25,introduced=3.7.0,fixed=3.7.10.

**Is there a fix for CVE-2026-71326?** Yes. github.com/traefik/traefik/v3 (Go): upgrade to 3.6.25, 3.7.10 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-71326 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-71326?** Check whether you run github.com/traefik/traefik (Go), github.com/traefik/traefik/v2 (Go), github.com/traefik/traefik/v3 (Go) or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/traefik/traefik/v3 (Go): upgrade to 3.6.25, 3.7.10 or later

  ```sh
  go get github.com/traefik/traefik/v3@v3.7.10
  ```


## Technical details

A vulnerability exists in Traefik's BasicAuth middleware where concurrent password verifications are deduplicated using a 'singleflight' group. The deduplication key is formed by the delimiter-free concatenation of the submitted password and the stored secret (hash). An attacker who knows a valid password 'P' and its corresponding hash 'H' can submit a request for an unconfigured username using 'P+H' as the password. Because the secret for an unconfigured user is an empty string, the resulting key ('P+H' + '') matches the key of a concurrent valid request ('P' + 'H'). If the valid request starts the calculation, the attacker's request receives the successful result and is forwarded to the backend with the attacker-specified username. This allows identity spoofing and privilege escalation, especially when Traefik is configured to forward the authenticated username via a header field. Patches are available in versions 3.6.25 and 3.7.10.

## Affected products

- Traefik Labs Traefik >= 3.6.11, <= 3.6.24
- Traefik Labs Traefik >= 3.7.0, <= 3.7.9

## Identifiers

- CVE-2026-71326
- GHSA-6765-c87h-8mrf
- GO-2026-6204

## Timeline

- 2026-08-03: disclosed: Initial disclosure on GitHub Advisories
- 2026-08-06: advisory: Updated advisory published

## References

- [https://api.github.com/users/hussst](https://api.github.com/users/hussst)
- [https://github.com/hussst](https://github.com/hussst)
- [https://api.github.com/users/hussst/gists%7B/gist_id%7D](https://api.github.com/users/hussst/gists%7B/gist_id%7D)
- [https://api.github.com/users/hussst/repos](https://api.github.com/users/hussst/repos)
- [https://avatars.githubusercontent.com/u/126237641?v=4](https://avatars.githubusercontent.com/u/126237641?v=4)
- [https://api.github.com/users/hussst/events%7B/privacy%7D](https://api.github.com/users/hussst/events%7B/privacy%7D)

## Related threats

- [Traefik BasicAuth singleflight username enumeration via timing oracle](https://junglewise.ai/threats/cve-2026-88010-traefik-basicauth-singleflight-username-enumeration-via-timing)
- [Traefik readTimeout not enforced on HTTP/3 connections](https://junglewise.ai/threats/cve-2026-88012-traefik-readtimeout-not-enforced-on-http-3-connections)
- [Traefik ForwardAuth identity spoofing via header alias](https://junglewise.ai/threats/cve-2026-88011-traefik-forwardauth-identity-spoofing-via-header-alias)
- [Traefik rootless HTTP/1 request-target routing bypass](https://junglewise.ai/threats/cve-2026-88009-traefik-rootless-http-1-request-target-routing-bypass)
- [Traefik HTTP request smuggling via unrestricted protocol upgrade](https://junglewise.ai/threats/cve-2026-88008-traefik-http-request-smuggling-via-unrestricted-protocol-upgrade)