Vulnerability in Traefik
CVE-2026-48491
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.
EPSS: 0.004 (29.4th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 10.0 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N.
Affected products
- Traefik — versions >= 3.7.0, < 3.7.3
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Exploit, Patch, Mailing List, Vendor Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC, Release Notes)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Frequently asked questions
- What is CVE-2026-48491?
- CVE-2026-48491 is a critical-severity vulnerability in Traefik, classified under Authentication Bypass Using an Alternate Path or Channel. CVSS score: 10.0/10. Published 2026-06-23.
- How severe is CVE-2026-48491?
- Critical severity. CVSS v3 base score is 10.0 out of 10.