CVE-2026-48491 Details
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.
A high-severity vulnerability has been identified in Traefik versions 3.7.0 prior to 3.7.3. The issue lies in Traefik's domain-fronting protection, specifically the SNICheck feature, which allows an unauthenticated client to bypass mutual TLS requirements enforced through wildcard router TLSOptions. When a router is configured with a wildcard host rule, such as Host(*.example.com), and stricter TLS options like RequireAndVerifyClientCert, the SNICheck only applies exact map lookups for the HTTP Host header, ignoring wildcard matching. This creates an opportunity for an attacker to exploit the vulnerability by completing the TLS handshake under permissive options and then targeting the wildcard-protected backend with an HTTP Host header, all without presenting a client certificate. This vulnerability affects the regular HTTPS and HTTP/2 paths, but does not require HTTP/3.
Users can upgrade to Traefik version 3.7.3 to address this vulnerability.
Metrics
CVSS 4.0 Severity and Vector Strings:
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Jun 24, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://access.redhat.com/errata/RHSA-2026:62260 | redhat-SADP | |
| https://access.redhat.com/security/cve/CVE-2026-48491 | redhat-SADP | |
| https://bugzilla.redhat.com/show_bug.cgi?id=2491923 | redhat-SADP | |
| https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-48491.json | redhat-SADP | |
| https://github.com/traefik/traefik/releases/tag/v3.7.3 | [email protected] | PatchRelease Notes |
| https://github.com/traefik/traefik/security/advisories/GHSA-5r4w-85f3-pw66 | [email protected] | ExploitMailing ListPatchVendor Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-288 | Authentication Bypass Using an Alternate Path or Channel | [email protected] |
| CWE-807 | Reliance on Untrusted Inputs in a Security Decision | redhat-SADP |
Affected Products
| Product | Versions |
|---|---|
| traefik traefik | >= 3.7.0, < 3.7.3 |
CPE
Remediation
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Change History
7 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Sep 2, 2026 | CVE Modified | redhat-SADP |
| Sep 2, 2026 | CVE Modified | [email protected] |
| Jul 15, 2026 | CVE Modified | redhat-SADP |
| Jun 30, 2026 | CVE Modified | redhat-SADP |
| Jun 26, 2026 | Initial Analysis | [email protected] |
| Jun 24, 2026 | CVE Modified | CISA-ADP |
| Jun 23, 2026 | New CVE Received | [email protected] |