CVE-2026-48491
CriticalCVSS 10.0Exploitation Probability (EPSS)
Low risk16th percentile - higher than 16% of all known CVEs
Summary
In Traefik versions 3.7.0 through 3.7.3, a vulnerability in the domain-fronting protection (SNICheck) allows an unauthenticated client to bypass mutual TLS enforced by wildcard router rules. The attacker can complete a TLS handshake under permissive options for a different SNI and then send an HTTP request with a Host header targeting the wildcard-protected backend without presenting a client certificate.
Risk Assessment
The organization faces the risk of unauthorized access to services protected by mutual TLS, potentially leading to breaches of confidentiality and integrity of data transmitted to those services.
Recommendation
Immediately upgrade Traefik to version 3.7.3 or later, which contains the fix for this vulnerability.
Original NVD description (English source)
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.