Authentication bypass using an alternate path or channel in Traefik - CVE-2026-48491
Published: July 3, 2026
Vulnerability identifier: #VU136871
CSH Severity: High
CVSS v4: 8.8 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:H/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-48491
CWE-ID: CWE-288
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass mutual TLS authentication and access protected backends.
The vulnerability exists due to improper authentication in SNICheck when resolving TLSOptions for wildcard host rules during domain-fronted HTTPS or HTTP/2 requests. A remote attacker can complete a TLS handshake using a permissive SNI and then send a crafted Host header targeting a wildcard-protected backend to bypass mutual TLS authentication and access protected backends.
Exploitation requires a wildcard-protected router with stricter TLS options and another permissive SNI served on the same entrypoint.
Affected software
Traefik
How to mitigate CVE-2026-48491
Install security update from vendor's website.
Traefik - update to 3.7.3