CVE-2026-48491: Traefik mTLS bypass in SNICheck via wildcard domain fronting

CVE-2026-48491 · Severity: high · CVSS 3.1 · Published 2026-06-23

Traefik is a popular open-source tool used to route and manage web traffic. A security flaw in its domain-fronting protection allows unauthorized users to bypass security requirements, such as digital certificates (mTLS), when accessing certain protected websites. By using a "permissive" connection to one site and then switching the request to a "protected" site that uses wildcard rules (like *.example.com), an attacker can gain access to sensitive internal services without the required credentials.

Technologies: github.com/traefik/traefik/v2 (Go), github.com/traefik/traefik/v3 (Go), Traefik Labs Traefik Proxy. Vendors: Go, Traefik Labs.

Quick answers

Is CVE-2026-48491 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-48491 being exploited in the wild.
How severe is CVE-2026-48491?
High severity, with a CVSS score of 3.1, published 23 June 2026.
Which products and versions are affected?
github.com/traefik/traefik/v2 (Go) SEMVER:introduced=0,fixed=2.11.48; github.com/traefik/traefik/v3 (Go) SEMVER:introduced=3.7.0,fixed=3.7.3; Traefik Labs Traefik Proxy >= 3.7.0, <= 3.7.1.
Is there a fix for CVE-2026-48491?
Yes. github.com/traefik/traefik/v2 (Go): upgrade to 2.11.48 or later; github.com/traefik/traefik/v3 (Go): upgrade to 3.7.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-48491 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-48491?
Check whether you run github.com/traefik/traefik/v2 (Go), github.com/traefik/traefik/v3 (Go) or Traefik Labs Traefik Proxy at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • github.com/traefik/traefik/v2 (Go): upgrade to 2.11.48 or later
    go get github.com/traefik/traefik/v2@v2.11.48
  • github.com/traefik/traefik/v3 (Go): upgrade to 3.7.3 or later
    go get github.com/traefik/traefik/v3@v3.7.3

Technical details

A vulnerability exists in Traefik's SNICheck middleware where it resolves TLS options for the HTTP Host header using exact map lookups only, failing to account for wildcard host rules (e.g., Host(*.example.com)). If a router is configured with a wildcard host and strict TLSOptions (such as RequireAndVerifyClientCert), an attacker can perform a 'domain-fronting' attack. By completing a TLS handshake using a different, permissive SNI on the same entrypoint and then sending an HTTP Host header targeting the wildcard-protected backend, the attacker bypasses the mTLS requirement. This occurs because SNICheck incorrectly classifies the wildcard-protected host as using default (permissive) TLS options. The issue affects HTTPS/HTTP-2 paths in versions 3.7.0 through 3.7.2 and is fixed in version 3.7.3.

Affected products

  • Traefik Proxy Traefik >= 3.7.0, < 3.7.3

Identifiers

  • CVE-2026-48491
  • GHSA-5r4w-85f3-pw66
  • GO-2026-5152

Timeline

  • 2026-06-05: advisory: GitHub Security Advisory published
  • 2026-06-04: patched: Version 3.7.3 released
  • 2026-06-23: disclosed: CVE-2026-48491 published to NVD

References

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