# CVE-2026-41263: Traefik: A timing side-channel vulnerability allows for valid username enumeration via BasicAuth middleware

Source: https://junglewise.ai/threats/cve-2026-41263-traefik-a-timing-side-channel-vulnerability-allows-for-valid  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-30  
License: CC BY 4.0 with a link back

CVE-2026-41263 · Severity: low · CVSS 3.7 · Published 2026-04-30

Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.43, 3.6.14, and 3.7.0-rc.2, there is a timing side-channel vulnerability in Traefik's BasicAuth middleware that allows an attacker to enumerate valid usernames through response-time differences. The variable intended to hold a constant-time fallback secret always resolves to an empty string, causing the constant-time comparison to short-circuit in microseconds rather than performing a full bcrypt evaluation. This restores the original timing oracle and makes it possible to distinguish existing users from non-existing ones by measuring authentication response times. This issue has been patched in versions 2.11.43, 3.6.14, and 3.7.0-rc.2.

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](https://junglewise.ai/threats/technologies/traefik). Vendors: [Go](https://junglewise.ai/threats/vendors/go), [Traefik](https://junglewise.ai/threats/vendors/traefik).

## Quick answers

**Is CVE-2026-41263 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-41263 being exploited in the wild.

**How severe is CVE-2026-41263?** Low severity, with a CVSS score of 3.7, published 30 April 2026.

**Which products and versions are affected?** github.com/traefik/traefik (Go) SEMVER:introduced=0, SEMVER:introduced=0,last_affected=1.7.34; github.com/traefik/traefik/v2 (Go) SEMVER:introduced=0,fixed=2.11.43; github.com/traefik/traefik/v3 (Go) SEMVER:introduced=3.0.0-beta1,fixed=3.6.14,introduced=3.7.0-ea.1,fixed=3.7.0-rc.2, SEMVER:introduced=3.7.0-ea.1,fixed=3.7.0-rc.2.

**Is there a fix for CVE-2026-41263?** Yes. github.com/traefik/traefik/v2 (Go): upgrade to 2.11.43 or later; github.com/traefik/traefik/v3 (Go): upgrade to 3.7.0-rc.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-41263?** 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/v2 (Go): upgrade to 2.11.43 or later

  ```sh
  go get github.com/traefik/traefik/v2@v2.11.43
  ```

- github.com/traefik/traefik/v3 (Go): upgrade to 3.7.0-rc.2 or later

  ```sh
  go get github.com/traefik/traefik/v3@v3.7.0-rc.2
  ```


## Affected products

- github.com/traefik/traefik (Go) SEMVER:introduced=0, SEMVER:introduced=0,last_affected=1.7.34
- github.com/traefik/traefik/v2 (Go) SEMVER:introduced=0,fixed=2.11.43
- github.com/traefik/traefik/v3 (Go) SEMVER:introduced=3.0.0-beta1,fixed=3.6.14,introduced=3.7.0-ea.1,fixed=3.7.0-rc.2, SEMVER:introduced=3.7.0-ea.1,fixed=3.7.0-rc.2
- Traefik

## Identifiers

- CVE-2026-41263
- GHSA-6x2q-h3cr-8j2h
- GO-2026-5195

## Related threats

- [Traefik ForwardAuth connection pool identity leak via NTLM/Negotiate](https://junglewise.ai/threats/cve-2026-121966-traefik-2-x-before-2-11-60-and-3-x-before-3-7-16-sends)
- [Traefik FastProxy data race in HTTP/1 upgrades](https://junglewise.ai/threats/cve-2026-119574-traefik-from-3-2-0-before-3-7-15-contains-a-data-race-in-the)
- [Traefik authentication bypass in TLS options resolution](https://junglewise.ai/threats/cve-2026-114656-traefik-before-2-11-58-and-3-7-13-contains-an-authentication)
- [Traefik NTLM/Kerberos TLS configuration bypass](https://junglewise.ai/threats/cve-2026-114642-traefik-2-11-0-before-2-11-58-and-3-0-0-before-3-7-14-stores-its)
- [Traefik authentication bypass in backend connection pool](https://junglewise.ai/threats/cve-2026-114639-traefik-2-11-0-before-2-11-58-and-3-0-0-before-3-7-14-contains)