high CVSS 8.2 EPSS 0.44%

CVE-2026-88009·Traefik vulnerability

Traefik is an open source HTTP reverse proxy and load balancer. Prior to 2.11.57, and 3.7.13, Traefik accepts a rootless HTTP/1 request target that Go stores in URL.Opaque while leaving URL.Path empty. The rewriteRequestBuilder path evaluates routing, path sanitization, forwardAuth, encodedCharacters, and access logging against a path normalized to / but forwards URL.Opaque verbatim to the backend, allowing cross-vhost routing bypass, path-scoped authorization bypass, and access-log evasion when the backend interprets the opaque target as a path. This issue is fixed in 2.11.57 and 3.7.13.

Severity
high
Software
Traefik
Fixed in
3.7.13
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 0.44% — higher than 37% 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-2026-88009 scores 8.2 on CVSS, so a successful attack would be serious — but at 0.44%, 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: 3.7.13

Fixed in: 3.7.13

How to fix this CVE

Upgrade Traefik to version 3.7.13 or later to resolve a critical HTTP request handling flaw that allows attackers to bypass routing policies and authorization controls. Organizations running versions 3.0.0 through 3.7.12 should prioritize this update immediately, as the vulnerability permits malicious actors to route requests to unintended backends and evade security logging.

sudo dnf install -y traefik-3.7.13 (via EPEL or Traefik official repository)

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

GET / HTTP/1.1\r\nHost: backend.example.com\r\n|POST .*?HTTP/1\.1 with encoded or opaque request targets (e.g., requests missing standard path formatting but targeting backend services)

WAF mitigation (if patching is not yet possible)

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

Implement WAF rules to reject HTTP/1.1 requests with malformed or opaque request targets (e.g., targets that do not begin with '/' or contain unexpected percent-encoding patterns). Monitor for requests where the Host header and request target path are mismatched relative to expected routing rules.

How to check if you are affected

  1. Step 1: Verify installed Traefik version by running: traefik version or checking docker ps for the image tag if containerized
  2. Step 2: Confirm if Traefik is exposed to untrusted HTTP/1.1 traffic by reviewing your ingress configuration and network policies
  3. Step 3: Search Traefik access logs for HTTP requests with malformed request targets (Check for requests with unusual URL encoding or missing path segments while targeting different backends than expected)
  4. Step 4: After upgrading, validate the fix by restarting Traefik (systemctl restart traefik or container redeploy) and confirm version output shows 3.7.13 or higher

FAQ

What is CVE-2026-88009?

A vulnerability in Traefik's HTTP/1 request handling where rootless request targets are processed inconsistently—the reverse proxy evaluates routing rules and authorization against a normalized path, but forwards the original unmodified request target to backend servers, allowing security controls to be bypassed.

Is CVE-2026-88009 being actively exploited?

No, this vulnerability is not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits have been disclosed. However, the flaw is easily discoverable and should be patched promptly.

What versions of Traefik are affected by CVE-2026-88009?

Traefik versions 3.0.0 through 3.7.12 are affected. Version 2.x users on versions prior to 2.11.57 should also upgrade.

How do I check if my server is vulnerable to CVE-2026-88009?

Run 'traefik version' or check your container image tag to determine the installed version. If it is between 3.0.0 and 3.7.12 (or 2.0.0 and 2.11.56 for v2), your instance is vulnerable.

Does Defensia detect CVE-2026-88009?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Traefik is installed on a monitored server, CVE-2026-88009 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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