critical CVSS 10 EPSS 0.63%

CVE-2026-53622·Traefik vulnerability

Traefik 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.

Severity
critical
Software
Traefik
Fixed in
3.7.3
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 0.63% — higher than 48% 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-2026-53622 scores 10 on CVSS, so a successful attack would be serious — but at 0.63%, 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: 3.7.3

Fixed in: 3.7.3

How to fix this CVE

Upgrade Traefik to version 3.7.3 or later (also 3.6.18 or 2.11.51 for older branches) to resolve the HTTP/3 TLS handshake bypass vulnerability. If HTTP/3 is not required for your deployment, disable QUIC on affected entrypoints as an interim mitigation. Verify that wildcard Host rules and case-insensitive hostname matching are properly validated after the upgrade.

sudo dnf update traefik

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

QUIC ClientHello packet with SNI containing wildcard or case-variant hostname (e.g., *.example.com or Example.COM) followed by successful TLS handshake without client certificate, then HTTP/2 request routed to mTLS-protected path

WAF mitigation (if patching is not yet possible)

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

Implement UDP rate limiting on port 443 (QUIC) to restrict QUIC connection attempts; block or challenge QUIC ClientHello packets with SNI values matching wildcard patterns until patched. This does not replace the need for patching.

How to check if you are affected

  1. Step 1: Check Traefik version with `traefik version` or inspect the running container `docker ps --no-trunc | grep traefik && docker exec <container_id> traefik version`
  2. Step 2: Verify HTTP/3 is enabled in your Traefik configuration by checking entrypoint settings for `http3: {}` or `protocol: udp` in static config files or command-line arguments
  3. Step 3: Search logs for QUIC/UDP connection attempts that bypass mTLS policies, looking for entries like `TLS handshake completed without client cert` followed by router dispatch to mTLS-protected backends
  4. Step 4: After upgrading, confirm the version with `traefik version` and verify SNI matching against wildcard patterns works correctly by testing connections with `openssl s_client -connect <host>:443 -servername *.example.com`

FAQ

What is CVE-2026-53622?

This critical vulnerability in Traefik's HTTP/3 implementation allows attackers to bypass client certificate (mTLS) requirements by exploiting case-sensitive SNI lookups that fail to match wildcard hostnames. The QUIC handshake can complete without a certificate, then route to backends that should require one.

Is CVE-2026-53622 being actively exploited?

No, this vulnerability is not currently listed in CISA's Known Exploited Vulnerabilities catalog, and no public exploits are available. However, given its critical CVSS 10.0 score and ease of exploitation, patching should be prioritized immediately.

What versions of Traefik are affected by CVE-2026-53622?

Versions 3.7.0 through 3.7.2, 3.6.0 through 3.6.17, and 2.11.0 through 2.11.50 are vulnerable. Fixed versions are 3.7.3, 3.6.18, and 2.11.51.

How do I check if my server is vulnerable to CVE-2026-53622?

Run `traefik version` and confirm HTTP/3 is enabled by examining your Traefik config file for `http3:` or `protocol: udp` settings in entrypoints. If your version is below 3.7.3 (or equivalent in your branch) AND HTTP/3 is enabled, you are vulnerable.

Does Defensia detect CVE-2026-53622?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Traefik is installed on a monitored server, CVE-2026-53622 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-2026-48020CVSS 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.
CVE-2026-85595CVSS 9.8Traefik versions before v2.11.55 and versions v3.0.0 through v3.7.10 contain an authentication bypass vulnerability in the digestAuth middleware where unknown usernames receive an empty secret instead of rejection. Attackers can compute a valid digest response using the empty secret and arbitrary credentials to bypass authentication on any digestAuth-protected route without a valid username or password.

References

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