high CVSS 8.7 EPSS 0.19%

CVE-2026-114640·Traefik vulnerability

Traefik from v3.7.0 before v3.7.14 contains an authentication bypass vulnerability in its Kubernetes Ingress-NGINX provider that forwards client-supplied Ssl-Client-* headers on the plaintext HTTP router. When ssl-redirect is disabled alongside auth-tls-pass-certificate-to-upstream, unauthenticated attackers can send Ssl-Client-Verify: SUCCESS with a chosen certificate subject and issuer to impersonate mTLS identities.

Severity
high
Software
Traefik
Fixed in
3.7.14
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at 0.19% — higher than 9% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2026-114640 scores 8.7 on CVSS, so a successful attack would be serious — but at 0.19%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

From: 3.7.0

Until: 3.7.14

Fixed in: 3.7.14

How to fix this CVE

Upgrade Traefik immediately to version 3.7.14 or later to patch the mTLS header spoofing vulnerability. If you are running Kubernetes with Ingress-NGINX provider and have disabled ssl-redirect while enabling auth-tls-pass-certificate-to-upstream, this configuration is currently at risk of authentication bypass. Review your Traefik configuration to ensure these settings are not both active simultaneously until the upgrade is complete.

sudo dnf update traefik

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST|GET request containing header pattern `Ssl-Client-Verify:\s*SUCCESS` paired with `Ssl-Client-Subject:` or `Ssl-Client-Issuer:` headers to HTTP (not HTTPS) endpoints protected by mTLS policy

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Block or sanitize inbound HTTP requests containing Ssl-Client-* headers (Ssl-Client-Verify, Ssl-Client-Subject, Ssl-Client-Issuer, Ssl-Client-Cert). These headers should only be set by terminating TLS proxies, never forwarded from client requests. Implement a WAF rule: `SecRule REQUEST_HEADERS:Ssl-Client-Verify "@rx .+" "id:100001,phase:2,deny,status:403,msg:'Spoofed mTLS header detected'"` (ModSecurity syntax).

How to check if you are affected

  1. Step 1: Check installed Traefik version with `traefik version` or `docker exec <container_id> traefik version` if containerized
  2. Step 2: Verify if Kubernetes Ingress-NGINX provider is configured in your Traefik config file (check for `providers.kubernetesIngress` or `ingressClass: nginx`)
  3. Step 3: Confirm if ssl-redirect is disabled and auth-tls-pass-certificate-to-upstream is enabled in your static or dynamic configuration files
  4. Step 4: After upgrading, re-run `traefik version` to confirm version 3.7.14 or later is installed

FAQ

What is CVE-2026-114640?

This vulnerability allows unauthenticated attackers to forge mTLS client certificates by injecting spoofed SSL-Client-* HTTP headers when Traefik's Ingress-NGINX provider is misconfigured with ssl-redirect disabled and certificate-pass-through enabled. An attacker can claim any certificate subject/issuer without providing a valid certificate, bypassing mutual TLS authentication controls.

Is CVE-2026-114640 being actively exploited?

No, this vulnerability is not currently listed on CISA's Known Exploited Vulnerabilities (KEV) catalog, and no public exploits have been released. However, the attack is trivial to execute and organizations should patch immediately.

What versions of Traefik are affected by CVE-2026-114640?

Traefik versions 3.7.0 through 3.7.13 are vulnerable. Version 3.7.14 and later contain the fix.

How do I check if my server is vulnerable to CVE-2026-114640?

Run `traefik version` to confirm your version is between 3.7.0 and 3.7.13, then check your Traefik configuration for both `ssl-redirect: false` and `auth-tls-pass-certificate-to-upstream: true` in the Kubernetes Ingress provider settings.

Does Defensia detect CVE-2026-114640?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Traefik is installed on a monitored server, CVE-2026-114640 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

Track CVEs across your fleet automatically

Defensia scans your Linux servers and tells you exactly which ones are running vulnerable versions — including CVE-2026-114640. Free for 1 server.

Get started free