CVE-2026-41263 Traefik: BasicAuth middleware: timing side-channel vulnerability

What is CVE-2026-41263?

CVE-2026-41263 is a medium-severity vulnerability in Traefik Traefik, published on 30 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

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.

Weakness: CWE-208

Which versions are affected by CVE-2026-41263?

11 open source packages ship an affected version, including github.com/traefik/traefik/v3, github.com/traefik/traefik and github.com/traefik/traefik/v2. It affects 1 product.

Products include Traefik Traefik.

How do I fix CVE-2026-41263?

Upgrade github.com/traefik/traefik/v3 to a fixed version for your release line: 3.6.14 or 3.7.0-rc.2.

Is CVE-2026-41263 being exploited?

There is no known exploitation of CVE-2026-41263 in the wild and no public exploit code.

Other vulnerabilities in Traefik Traefik

• CVE-2024-45410 HTTP client can remove the X-Forwarded headers in Traefik Critical 9.8
• CVE-2026-88877 Traefik v3.7.0 Authentication Bypass via from-to-www-redirect Critical 9.3
• CVE-2026-85595 Traefik before v2.11.55 and v3.0.0 through v3.7.10 Authentication Bypass via digestAuth Critical 9.3
• CVE-2026-88007 Traefik HTTP/3 Backend NTLM Connection Reuse Critical 9.1
• CVE-2026-88009 Traefik: Rootless HTTP/1 request-target routes as "/" but is forwarded verbatim, bypassing path-scoped routing, middleware guards and access logging High 8.8

All Traefik Traefik vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as CLEANSTART-2026-HD64585, GHSA-6x2q-h3cr-8j2h, GO-2026-5195, MINI-774v-rpcw-8ffc, MINI-7g79-rmjr-qfx4, MINI-f5q6-jfx8-m78r.