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

Source: https://junglewise.ai/threats/cve-2026-48491-traefik-mtls-bypass-in-snicheck-via-wildcard-domain-fronting  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-23. Updated: 2026-06-23  
License: CC BY 4.0 with a link back

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)](https://junglewise.ai/threats/technologies/github-com-traefik-traefik-v2), [github.com/traefik/traefik/v3 (Go)](https://junglewise.ai/threats/technologies/github-com-traefik-traefik-v3), [Traefik Labs Traefik Proxy](https://junglewise.ai/threats/technologies/traefik-proxy). Vendors: [Go](https://junglewise.ai/threats/vendors/go), [Traefik Labs](https://junglewise.ai/threats/vendors/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

  ```sh
  go get github.com/traefik/traefik/v2@v2.11.48
  ```

- github.com/traefik/traefik/v3 (Go): upgrade to 3.7.3 or later

  ```sh
  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

- [https://github.com/traefik/traefik/releases/tag/v3.7.3](https://github.com/traefik/traefik/releases/tag/v3.7.3)
- [https://github.com/traefik/traefik/security/advisories/GHSA-5r4w-85f3-pw66](https://github.com/traefik/traefik/security/advisories/GHSA-5r4w-85f3-pw66)

## Related threats

- [Traefik readTimeout not enforced on HTTP/3 connections](https://junglewise.ai/threats/cve-2026-88012-traefik-readtimeout-not-enforced-on-http-3-connections)
- [Traefik ForwardAuth identity spoofing via header alias](https://junglewise.ai/threats/cve-2026-88011-traefik-forwardauth-identity-spoofing-via-header-alias)
- [Traefik rootless HTTP/1 request-target routing bypass](https://junglewise.ai/threats/cve-2026-88009-traefik-rootless-http-1-request-target-routing-bypass)
- [Traefik HTTP request smuggling via unrestricted protocol upgrade](https://junglewise.ai/threats/cve-2026-88008-traefik-http-request-smuggling-via-unrestricted-protocol-upgrade)
- [Traefik HTTP/3 backend NTLM connection reuse](https://junglewise.ai/threats/cve-2026-88007-traefik-http-3-backend-ntlm-connection-reuse)