high CVSS 7.4

CVE-2026-88004·Traefik vulnerability

Traefik is an open source HTTP reverse proxy and load balancer. From 3.2.0 until 3.7.13, Traefik entrypoint defenses aliasHeadersStrategy, underscoreHeadersStrategy, and forwardedHeaders inspect req.Header but not req.Trailer, allowing an unauthenticated client to submit an aliasing or trusted header name in an HTTP/1.1 chunked trailer or an HTTP/2 trailer. When the retry or buffering middleware reads the body before the reverse proxy clones the request, the attacker-controlled trailer value reaches a backend that merges trailers into the header namespace, bypassing the documented delete or reject behavior and potentially spoofing identity or forwarded routing data. This issue is fixed in 3.7.13.

Severity
high
Software
Traefik
Fixed in
3.7.13
Published

Affected versions

From: 3.2.0

Until: 3.7.13

Fixed in: 3.7.13

How to fix this CVE

Update Traefik to version 3.7.13 or later to patch the HTTP trailer header spoofing vulnerability. This fix ensures that entrypoint defenses properly validate all header sources, including HTTP/1.1 chunked trailers and HTTP/2 trailers, preventing attackers from bypassing authentication or routing controls through trailer injection.

sudo dnf update traefik

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST|GET /.*HTTP/1\.1.*\r\nTransfer-Encoding: chunked.*Trailer:.*Authorization|X-Forwarded-For|X-Real-IP

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 strictly validate HTTP/1.1 requests with chunked Transfer-Encoding that include Trailer headers containing sensitive header names (Authorization, X-Forwarded-For, X-Real-IP, X-Forwarded-Proto). Additionally, enforce HTTP/2 trailer header validation at ingress to reject trailers with header field names that duplicate or override critical security headers.

How to check if you are affected

  1. Step 1: Check installed Traefik version with `traefik version` or inspect the binary at `/usr/bin/traefik --version`
  2. Step 2: Verify if aliasHeadersStrategy, underscoreHeadersStrategy, or forwardedHeaders are enabled in your traefik.yaml or static config by searching for these keys: `grep -E '(aliasHeadersStrategy|underscoreHeadersStrategy|forwardedHeaders)' /etc/traefik/traefik.yaml`
  3. Step 3: Check Traefik logs for suspicious trailer headers or chunked encoding requests with header-like values: `grep -i 'trailer\|chunked' /var/log/traefik/traefik.log | head -20`
  4. Step 4: Confirm the patch by running `traefik version` and verifying the version is 3.7.13 or higher, or check the commit hash in the binary metadata

FAQ

What is CVE-2026-88004?

A header validation bypass in Traefik that allows attackers to inject malicious headers through HTTP trailers, circumventing entrypoint security policies designed to block or delete sensitive headers. This can lead to authentication bypass or request routing manipulation.

Is CVE-2026-88004 being actively exploited?

No, there are no reports of active exploitation or publicly available exploits as of the current advisory date. However, the vulnerability requires only network access and no authentication, making it a high-priority target for opportunistic attacks.

What versions of Traefik are affected by CVE-2026-88004?

Traefik versions 3.2.0 through 3.7.12 are vulnerable. Version 3.7.13 and later contain the security fix.

How do I check if my server is vulnerable to CVE-2026-88004?

Run `traefik version` or inspect `/usr/bin/traefik --version` and compare against 3.7.13. If your version is between 3.2.0 and 3.7.12, you are vulnerable.

Does Defensia detect CVE-2026-88004?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Traefik is installed on a monitored server, CVE-2026-88004 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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