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

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), github.com/traefik/traefik/v2 (Go), github.com/traefik/traefik/v3 (Go), Traefik. Vendors: Go, 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
    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
    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

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.