Traefik 3.7.0-3.7.3: SNICheck wildcard bypass allows client cert bypass
CVE-2026-48491 Published on June 23, 2026
Traefik: SNICheck ignores wildcard TLSOptions mappings, allowing domain-fronted mTLS bypass
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.
Vulnerability Analysis
CVE-2026-48491 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have a high impact on confidentiality and integrity, and no impact on availability.
Weakness Types
Authentication Bypass Using an Alternate Path or Channel
A product requires authentication, but the product has an alternate path or channel that does not require authentication.
Reliance on Untrusted Inputs in a Security Decision
The application uses a protection mechanism that relies on the existence or values of an input, but the input can be modified by an untrusted actor in a way that bypasses the protection mechanism.
Products Associated with CVE-2026-48491
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Affected Versions
traefik:- Version >= 3.7.0, < 3.7.3 is affected.