Vulnerability · Published Apr 30, 2026 · Assigned by GitHub_M

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

Medium 6.3

In plain English

A medium-severity security flaw in traefik from traefik. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 31% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)6.3Medium

Exploit odds (30 days)0.4%top 69.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/traefik/traefik	no fix listed	GHSA-6x2q-h3cr-8j2h
Go	github.com/traefik/traefik	no fix listed	GO-2026-5195
Go	github.com/traefik/traefik/v2	2.11.43	GHSA-6x2q-h3cr-8j2h
Go	github.com/traefik/traefik/v2	2.11.43	GO-2026-5195
Go	github.com/traefik/traefik/v3	3.7.0-rc.2	GHSA-6x2q-h3cr-8j2h
Go	github.com/traefik/traefik/v3	3.6.14, 3.7.0-rc.2	GO-2026-5195
Go	github.com/traefik/traefik/v3	3.6.14	GHSA-6x2q-h3cr-8j2h

Affected products (as reported)

Vendor	Product	Versions
traefik	traefik	< 2.11.43>= 3.0.0-beta1, < 3.6.14>= 3.7.0-ea.1, < 3.7.0-rc.2

Weakness: CWE-208 · Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:N/SA:N

References

https://github.com/traefik/traefik/security/advisories/GHSA-6x2q-h3cr-8j2h x_refsource_CONFIRM
https://github.com/traefik/traefik/releases/tag/v2.11.43 x_refsource_MISC
https://github.com/traefik/traefik/releases/tag/v3.6.14 x_refsource_MISC
https://github.com/traefik/traefik/releases/tag/v3.7.0-rc.2 x_refsource_MISC