critical CVSS 9.1 EPSS 1.1%

CVE-2026-71324·Traefik vulnerability

Traefik is an open source HTTP reverse proxy and load balancer. Prior to 2.11.53, 3.6.24, and 3.7.9, Traefik's default HTTP reverse proxy forwards a plain HTTP/2 or HTTP/3 CONNECT request and its body to an HTTP/1.1 upstream through a shared net/http.Transport. When the upstream answers the CONNECT with a keep-alive non-2xx response and does not drain the body, Traefik returns the desynchronized backend socket to its shared pool and reuses it for other clients. An unauthenticated attacker can use this behavior to make a different client read the attacker's smuggled response, which can include authenticated or private content from another request. The ForwardAuth middleware with forwardBody true and preserveRequestMethod true can re-issue a CONNECT with the buffered body attached, exposing the auth-client pool to the same desynchronization. This issue is fixed in 2.11.53, 3.6.24, and 3.7.9.

Severity
critical
Software
Traefik
Fixed in
3.7.9
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 1.1% — higher than 64% 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.

Affected versions

From: 3.7.0

Until: 3.7.9

Fixed in: 3.7.9

How to fix this CVE

Upgrade Traefik to version 3.7.9 or later to patch a critical HTTP/2 and HTTP/3 CONNECT request handling vulnerability that can lead to response smuggling and unauthorized data disclosure. Organizations running versions 3.7.0 through 3.7.8 should prioritize this update immediately. The fix prevents socket desynchronization in the reverse proxy's connection pool, which could otherwise allow attackers to intercept responses intended for other clients.

sudo dnf update traefik --assumeyes

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST|GET.*HTTP/(2|3).*CONNECT.*\r\n.*Connection: keep-alive|HTTP/1\.1\s+(3\d{2}|4\d{2}|5\d{2}).*(?=(?:.*\r\n){0,5}\r\n[A-Za-z0-9])

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 rate-limit CONNECT tunnel requests from untrusted sources. Implement strict validation of upstream server responses to CONNECT requests, ensuring the response body is properly consumed before connection reuse. Consider enforcing HTTP/1.1 connections to upstream servers if HTTP/2 tunneling is not required.

How to check if you are affected

  1. Step 1: Check installed Traefik version with: traefik version or grep -i version /etc/traefik/traefik.yml
  2. Step 2: Verify if HTTP/2 or HTTP/3 CONNECT tunneling is enabled in your Traefik configuration by checking for 'http2' or 'http3' protocol settings in backends
  3. Step 3: Search Traefik access and error logs for patterns like 'CONNECT.*200' or '502 Bad Gateway' followed by mismatched response bodies using: grep -E 'CONNECT|502' /var/log/traefik/access.log
  4. Step 4: After patching, confirm the updated version is running with: traefik version && systemctl status traefik

FAQ

What is CVE-2026-71324?

This vulnerability allows connection pool poisoning in Traefik's reverse proxy when handling HTTP/2 or HTTP/3 CONNECT requests. If an upstream server responds with a non-2xx status while leaving the connection desynchronized, Traefik may reuse that corrupted connection for subsequent client requests, causing one client to receive another client's response data.

Is CVE-2026-71324 being actively exploited?

No, this vulnerability is not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog, and no public exploits are available. However, the critical CVSS score of 9.1 warrants immediate patching.

What versions of Traefik are affected by CVE-2026-71324?

Traefik versions 3.7.0 through 3.7.8 are vulnerable. Additionally, versions 2.x prior to 2.11.53 and 3.6.x prior to 3.6.24 are also affected. Upgrade to 3.7.9, 3.6.24, or 2.11.53 respectively.

How do I check if my server is vulnerable to CVE-2026-71324?

Run 'traefik version' to retrieve your installed version. If it falls within 3.7.0–3.7.8, 2.x before 2.11.53, or 3.6.x before 3.6.24, your server is vulnerable.

Does Defensia detect CVE-2026-71324?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Traefik is installed on a monitored server, CVE-2026-71324 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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