Traefik up to 3.7.2 wildcard-protected Backend authentication bypass

Summaryinfo

A vulnerability, which was classified as critical, has been found in Traefik up to 3.7.2. The affected element is an unknown function of the component wildcard-protected Backend. This manipulation causes authentication bypass. This vulnerability is handled as CVE-2026-48491. The attack can be initiated remotely. There is not any exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability classified as critical was found in Traefik up to 3.7.2. Affected by this vulnerability is an unknown functionality of the component wildcard-protected Backend. The manipulation with an unknown input leads to a authentication bypass vulnerability. The CWE definition for the vulnerability is CWE-288. A product requires authentication, but the product has an alternate path or channel that does not require authentication. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

Traefik is an HTTP reverse proxy and load balancer. From 3.7.0 until 3.7.3, there is a high severity vulnerability in Traefik's domain-fronting protection (SNICheck) that allows an unauthenticated client to bypass mutual TLS enforced through wildcard router TLSOptions. When a router uses a wildcard host rule such as Host(*.example.com) with stricter TLS options (for example RequireAndVerifyClientCert), SNICheck resolves the TLS options for the HTTP Host header using exact map lookups only and never applies wildcard matching. If another permissive SNI is served on the same entrypoint, an attacker can complete the TLS handshake under the permissive options and then send an HTTP Host header targeting the wildcard-protected backend, reaching it without presenting a client certificate. This affects the regular HTTPS / HTTP-2 path and does not require HTTP/3. This vulnerability is fixed in 3.7.3.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-48491 since 05/21/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Neither technical details nor an exploit are publicly available.

Upgrading to version 3.7.3 eliminates this vulnerability. The upgrade is hosted for download at github.com.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Name

• Traefik

Version

• 3.7.0
• 3.7.1
• 3.7.2

Website

• Product: https://github.com/traefik/traefik/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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