medium CVSS 5.3 EPSS 0.42%

CVE-2026-88878·Traefik vulnerability

Traefik is an HTTP reverse proxy and load balancer. In versions >= v2.8.2 through <= v2.11.55 and >= v3.0.0 through <= v3.7.11, the entryPoints.<name>.transport.respondingTimeouts settings — notably readTimeout, which is enabled by default at 60s — are not applied to the HTTP/3 request path. readTimeout is enforced as a deadline on the underlying TCP connection, which cannot be applied to a QUIC stream, and Traefik's HTTP/3 server is constructed without any timeout. As a result, on entry points with HTTP/3 enabled, an unauthenticated remote client that trickles request body bytes can hold a request open indefinitely and, with it, one upstream connection per request, exhausting bounded backend connection pools and causing denial of service. The issue was introduced in v2.8.2 when a quic-go API change removed the embedded http.Server that carried these timeouts. Fixed in v2.11.56 and v3.7.12.

Severity
medium
Software
Traefik
Fixed in
3.7.12
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 0.42% — higher than 36% 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: 3.0.0

Until: 3.7.12

Fixed in: 3.7.12

How to fix this CVE

Upgrade Traefik to version 3.7.12 or later to resolve the HTTP/3 timeout bypass vulnerability. This update restores proper request timeout enforcement on QUIC streams, preventing resource exhaustion attacks. Organizations running versions 3.0.0 through 3.7.11 should prioritize this patch, especially if HTTP/3 is enabled on entry points.

sudo dnf update traefik-3.7.12 -y

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST|GET|PUT.*HTTP/3.*\r\n.*Content-Length:\s*[0-9]{4,}.*\r\n\r\n[\s\S]{0,100}(?!.*\r\n\r\n)

WAF mitigation (if patching is not yet possible)

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

Implement connection-level rate limiting on HTTP/3 traffic; enforce maximum request duration timeouts at the reverse proxy or WAF layer; consider disabling HTTP/3 until patched if it is not business-critical.

How to check if you are affected

  1. Step 1: Check installed Traefik version with `traefik version` or `docker inspect $(docker ps -q -f ancestor=traefik:latest) | grep -i version`
  2. Step 2: Verify HTTP/3 is enabled by checking the Traefik configuration file: `grep -A 5 'entryPoints' /etc/traefik/traefik.yml | grep -i 'http3\|quic'`
  3. Step 3: Search logs for incomplete or slow HTTP/3 requests: `grep -i 'http/3\|quic' /var/log/traefik/traefik.log | grep -v 'close\|finish' | head -20`
  4. Step 4: After patching, verify version with `traefik version` and confirm it reports v3.7.12 or later; test HTTP/3 connectivity with `curl --http3-only https://your-traefik-endpoint.local`

FAQ

What is CVE-2026-88878?

This vulnerability allows attackers to bypass request timeout settings on HTTP/3 connections in Traefik, enabling them to hold connections open indefinitely by trickling request body bytes. This exhausts backend connection pools and causes denial of service.

Is CVE-2026-88878 being actively exploited?

No, this vulnerability is not listed in CISA's KEV catalog and has no public exploits available, though the attack method is straightforward for motivated threat actors.

What versions of Traefik are affected by CVE-2026-88878?

Traefik versions 3.0.0 through 3.7.11 are vulnerable. The legacy v2 branch (v2.8.2 through v2.11.55) is also affected but fixed in v2.11.56.

How do I check if my server is vulnerable to CVE-2026-88878?

Run `traefik version` and confirm the version number; if it falls within 3.0.0–3.7.11, cross-reference your Traefik configuration to confirm HTTP/3 is enabled with `grep -i 'http3\|quic' /etc/traefik/traefik.yml`.

Does Defensia detect CVE-2026-88878?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Traefik is installed on a monitored server, CVE-2026-88878 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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