CVE-2026-48491
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.36%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
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.
- CVSS 4.0
- 7.8 HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 0.36% probability · 29th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-288, CWE-807
- Affected
- traefik/traefik
- Source
- security-advisories@github.com
References
- https://github.com/traefik/traefik/releases/tag/v3.7.3Patch, Release Notes
- https://github.com/traefik/traefik/security/advisories/GHSA-5r4w-85f3-pw66Exploit, Mailing List, Patch, Vendor Advisory
- https://access.redhat.com/errata/RHSA-2026:62260
- https://access.redhat.com/security/cve/CVE-2026-48491
- https://bugzilla.redhat.com/show_bug.cgi?id=2491923
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-48491.json
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.