critical CVSS 9.1 EPSS 0.35%

CVE-2026-85597·Traefik vulnerability

Traefik before v2.11.55 and v3.0.0 through v3.7.10 contain a TLS option conflict resolution vulnerability that allows unauthenticated attackers to bypass client-certificate authentication by creating conflicting TLS options on multi-host routers. Attackers can reach protected backends by exploiting shared TLS resolution across multiple hostnames in a single router rule, causing the strict mTLS requirement to fall back to default options for all hosts.

Severity
critical
Software
Traefik
Fixed in
3.7.11
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 0.35% — higher than 27% 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-2026-85597 scores 9.1 on CVSS, so a successful attack would be serious — but at 0.35%, 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: 3.0.0

Until: 3.7.11

Fixed in: 3.7.11

How to fix this CVE

Upgrade Traefik to version 3.7.11 or later to resolve the TLS option conflict vulnerability that allows mTLS authentication bypass. Organizations running Traefik 3.0.0 through 3.7.10 should prioritize this update immediately, as the vulnerability permits unauthenticated access to backends protected by mutual TLS. Review your router configurations after patching to ensure strict mTLS policies are properly enforced across all hostnames.

sudo dnf update traefik

Defensia detects this vulnerability

How to check if you are affected

  1. Run `traefik version` or check `/opt/traefik/traefik --version` to identify the currently installed version
  2. Review your Traefik configuration files (typically in /etc/traefik/traefik.yml or /etc/traefik/config/) for multi-host router rules with TLS options defined on the same rule
  3. Search Traefik access logs for requests from clients without valid certificates reaching protected backends: `grep -i 'tls' /var/log/traefik/access.log | grep -v 'subject='`
  4. After upgrading, restart Traefik (`sudo systemctl restart traefik`) and verify the new version with `traefik version`

FAQ

What is CVE-2026-85597?

This is a TLS configuration vulnerability in Traefik that allows attackers to bypass client-certificate authentication (mTLS) by exploiting conflicting TLS options on routers handling multiple hostnames, causing the strict mutual TLS requirement to be ignored.

Is CVE-2026-85597 being actively exploited?

No, this vulnerability is not currently listed in the CISA Known Exploited Vulnerabilities catalog, and no public exploit code is available at this time.

What versions of Traefik are affected by CVE-2026-85597?

Traefik versions 3.0.0 through 3.7.10 are vulnerable. Version 3.7.11 and later contain the patch. Versions earlier than 3.0.0 (including v2.x) are also affected if they have not been patched to v2.11.55 or later.

How do I check if my server is vulnerable to CVE-2026-85597?

Run `traefik version` and compare against 3.7.11; if your version is between 3.0.0 and 3.7.10 inclusive, you are vulnerable. Additionally, check if your Traefik configuration contains multi-host router rules with shared TLS options.

Does Defensia detect CVE-2026-85597?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Traefik is installed on a monitored server, CVE-2026-85597 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-2026-85597. Free for 1 server.

Get started free