CVE-2026-41263
Traefik: A timing side-channel vulnerability allows for valid username enumeration via BasicAuth middleware
Impact
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
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| go | github.com/traefik/traefik/v3 | >= 3.7.0-ea.1, < 3.7.0-rc.2 | 3.7.0-rc.2 |
| go | github.com/traefik/traefik/v2 | < 2.11.43 | 2.11.43 |
| go | github.com/traefik/traefik | <= 1.7.34 | none recorded |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Traefik | Traefik | before 2.11.43 from 3.0.0 before 3.6.14 Version 3.7.0 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-6x2q-h3cr-8j2h
- https://github.com/traefik/traefik/security/advisories/GHSA-6x2q-h3cr-8j2h
- https://github.com/traefik/traefik/releases/tag/v2.11.43
- https://github.com/traefik/traefik/releases/tag/v3.6.14
- https://github.com/traefik/traefik/releases/tag/v3.7.0-rc.2
- https://nvd.nist.gov/vuln/detail/CVE-2026-41263