high CVSS 7.5

CVE-2026-114656·Traefik vulnerability

Traefik before 2.11.58 and 3.7.13 contains an authentication bypass vulnerability that allows unauthenticated clients to skip client-certificate checks because negated Host matchers are counted as served domains. Attackers can reach backends protected by RequireAndVerifyClientCert when a router rule with !Host() creates a TLS options conflict that falls back to the default options.

Severity
high
Software
Traefik
Fixed in
3.7.13
Published

Affected versions

From: 3.0.0

Until: 3.7.13

Fixed in: 3.7.13

How to fix this CVE

Upgrade Traefik to version 2.11.58 or later to patch the mTLS bypass vulnerability. Organizations using older versions should prioritize this update as it resolves a logic flaw where negated Host matchers in router rules cause TLS configuration conflicts, allowing attackers to circumvent client certificate validation on protected backends. Apply the patch immediately if RequireAndVerifyClientCert is configured in your Traefik deployment.

sudo dnf update traefik

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

GET request to a backend protected by RequireAndVerifyClientCert without a valid client certificate in the TLS handshake, succeeding despite mTLS policy enforcement, combined with router rules containing negated Host matchers: (negated Host in config) AND (missing SSL_CLIENT_CERT in logs) AND (HTTP 200 response to protected endpoint)

How to check if you are affected

  1. Check installed Traefik version with: traefik version or curl http://localhost:8080/api/rawdata 2>/dev/null | grep -i version
  2. Identify routers with negated Host matchers by examining your traefik.yml or dynamic configuration files for rules containing !Host()
  3. Search Traefik access logs for TLS handshake failures followed by successful backend connections without valid client certificates: grep -i 'tls\|certificate\|ssl' /var/log/traefik/access.log
  4. Verify the patch by confirming traefik version output shows 2.11.58+ or 3.7.13+, then restart Traefik and test mTLS enforcement with an invalid client certificate request

FAQ

What is CVE-2026-114656?

This is an authentication bypass flaw in Traefik where negated Host matchers (!Host()) in router rules cause a TLS options conflict that defaults to permissive settings, allowing clients without valid certificates to access mTLS-protected backends.

Is CVE-2026-114656 being actively exploited?

No, this vulnerability is not currently listed on the CISA Known Exploited Vulnerabilities catalog, and no public exploits are available. However, the flaw is trivial to exploit once discovered, so patching should not be delayed.

What versions of Traefik are affected by CVE-2026-114656?

Traefik versions before 2.11.58 and before 3.7.13 are vulnerable. The exact affected version range starts from an undisclosed earlier version up to these fixed releases.

How do I check if my server is vulnerable to CVE-2026-114656?

Run 'traefik version' and compare against 2.11.58 or 3.7.13. If your version is lower, check your configuration for routers using negated Host matchers with RequireAndVerifyClientCert enabled: grep -r '!Host' /path/to/traefik/config

Does Defensia detect CVE-2026-114656?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Traefik is installed on a monitored server, CVE-2026-114656 will appear in your dashboard with remediation steps.

Related Traefik CVEs

CVE-2026-48491CVSS 10Traefik 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.
CVE-2026-54763CVSS 10Traefik is an HTTP reverse proxy and load balancer. Prior to v2.11.51, v3.6.22, and v3.7.6, Traefik's BasicAuth, DigestAuth, and ForwardAuth middlewares strip canonical-cased spoofed identity headers before writing Traefik's own value, but do not account for underscore-variant header names, which many backends normalize identically to dashed forms. An attacker able to reach a protected route can inject an underscore-variant header that survives Traefik's stripping and reaches the backend alongside, or on the unauthenticated ForwardAuth authResponseHeaders path instead of, the value Traefik intended to set, spoofing identity or authorization context. This issue is fixed in versions v2.11.51, v3.6.22, and v3.7.6.
CVE-2026-53622CVSS 10Traefik is an HTTP reverse proxy and load balancer. Versions prior to 3.7.3, 3.6.18, and 2.11.51 have a critical vulnerability in Traefik's HTTP/3 (QUIC) TLS configuration selection that allows unauthenticated clients to bypass router-specific mTLS enforcement. When HTTP/3 is enabled on an entrypoint, the TLS handshake selects the applicable TLS configuration through an exact, case-sensitive lookup on the SNI value, which fails to match wildcard host patterns (e.g., *.example.com) or case variants of the configured hostname. Because the handshake falls back to the default TLS configuration — which may not require client certificates — a client can complete the QUIC handshake without presenting a certificate, while the subsequent HTTP routing layer still dispatches the request to a backend protected by a router-specific mTLS policy. The issue affects deployments where HTTP/3 is enabled, a router uses a wildcard Host rule or case-insensitive hostname matching, a router-specific TLSOptions enforces client certificate authentication, and UDP access to the entrypoint is reachable by an attacker. This vulnerability is fixed in versions 3.7.3, 3.6.18, and 2.11.51.
CVE-2026-48020CVSS 10Traefik is an HTTP reverse proxy and load balancer. Prior to 2.11.48, 3.6.19, and 3.7.3, there is a high severity vulnerability in Traefik's StripPrefix middleware that allows an unauthenticated attacker to bypass route-level authentication and authorization. When a public router matches on a PathPrefix rule and applies the StripPrefix middleware, a request path containing .. or its percent-encoded form %2e%2e can match the public route at routing time and then, after the prefix is stripped and the path is normalized, resolve to a path served by a separate, authenticated router. As a result, an attacker can reach protected backend paths — such as admin or internal configuration endpoints — without satisfying the authentication middleware attached to the protected router. This vulnerability is fixed in 2.11.48, 3.6.19, and 3.7.3.
CVE-2026-44774CVSS 9.9Traefik is an HTTP reverse proxy and load balancer. Prior to 2.11.46, 3.6.17, and 3.7.1, Traefik's Kubernetes Gateway API provider allows a tenant with HTTPRoute creation permissions to expose the REST provider handler, bypassing the providers.rest.insecure=false setting. The Gateway provider accepts any TraefikService backend reference whose name ends with @internal, making it possible to route traffic to rest@internal in addition to the intended api@internal. In shared Gateway deployments where the REST provider is enabled, this allows a low-privileged actor to gain live dynamic configuration write access to Traefik, enabling unauthorized reconfiguration of routers and services. This vulnerability is fixed in 2.11.46, 3.6.17, and 3.7.1.

References

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