CVE-2026-88877
CriticalCVSS 9.8Summary
Traefik (HTTP reverse proxy and load balancer) in versions >= v3.7.0 and <= v3.7.11 has a flaw in the Kubernetes ingress-nginx provider for Ingresses carrying both an authentication annotation and the nginx.ingress.kubernetes.io/from-to-www-redirect annotation. The provider creates an additional 'sibling' router that matches on the host alone, carries only the RedirectRegex middleware, and still points at the parent router's protected backend service. Because RedirectRegex is not a terminal handler, a request its pattern does not match is forwarded to the backend, and because the redirect pattern only accepts a numeric port, a request with a non-numeric or empty port (e.g. 'Host: www.example.com:x') selects the sibling router, misses the redirect, and is proxied to the protected backend with none of the Ingress's annotation-derived middlewares applied. This discards not only authentication (e.g. BasicAuth) but every annotation-derived middleware, including source-IP allowlisting. Traefik v2 and v3 releases before v3.7.0 are not affected. The issue is fixed in v3.7.12.
Risk Assessment
An attacker can bypass authentication and other protections (e.g. IP allowlisting) and access the protected backend without authorization. This affects Kubernetes clusters using Traefik v3.7.0–v3.7.11 with the ingress-nginx provider and relevant annotations.
Recommendation
Upgrade Traefik to version v3.7.12 or later. Until patched, avoid combining authentication annotations with the from-to-www-redirect annotation in Ingresses.
Other vulnerabilities in Traefik
See all- CVE-2026-88012Medium
Traefik is an open source HTTP reverse proxy and load balancer. From 2.8.2 until 2.11.56 and 3.7.12, HTTP/3 entrypoints do not apply entryPoints..transport.respondingTimeouts.readTimeout because the timeout is enforced on a TCP connection and the HTTP/3 server has no corresponding QUIC stream deadline. An unauthenticated client can use a slow request body, trickling data indefinitely while holding a request and an upstream connection open and exhausting backends with bounded connection pools. This issue is fixed in 2.11.56 and 3.7.12.
- CVE-2026-88011Medium
Traefik is an open source HTTP reverse proxy and load balancer. Prior to 2.11.56, and from 3.0.0 until 3.7.12, a client-supplied dot-form header such as X.Authenticated.User survives ForwardAuth replacement and underscoreHeadersStrategy because Go treats it as distinct from X-Authenticated-User while normalization-prone CGI, WSGI, PHP, and NGINX backends collapse both names. A backend can consequently consume the client value instead of the identity Traefik asserted, allowing identity spoofing for any header managed by Traefik. The aliasHeadersStrategy protection is disabled by default and must be configured as delete or reject. The mitigation is available in 2.11.56 and 3.7.12.
- CVE-2026-88009High
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.
- CVE-2026-88008High
Traefik is an open source HTTP reverse proxy and load balancer. From 2.11.26 until 2.11.57 and 3.7.13, Traefik forwards a client-supplied Connection header requesting Upgrade, the Upgrade: h2c token, and HTTP2-Settings to a shared backend. If the backend accepts h2c and returns 101 Switching Protocols, Traefik enters a raw tunnel and no longer applies routers, BasicAuth, ForwardAuth, IPAllowList, RateLimit, access logging, metrics, or tracing to later HTTP/2 requests, allowing an unauthenticated request through an unprotected route to reach protected paths on the same backend. This issue is fixed in 2.11.57 and 3.7.13.
- CVE-2026-88004High
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.
- CVE-2026-88879Medium
Traefik v1.x, v2.x through v2.11.55, and v3.0.0 through v3.7.11 canonicalize header names only on dashes, so X-Auth-User, X_Auth_User, and X.Auth.User are treated as three distinct headers by Traefik, while backends that derive variable names from header names (CGI, WSGI, PHP, NGINX, and others) collapse them into a single variable. A client can smuggle a dot-form alias of a header managed by Traefik alongside the canonical version, e.g., X.Authenticated.User alongside X-Authenticated-User, causing the backend to read the client-supplied value instead of the identity Traefik asserted.
- CVE-2026-88878Medium
Traefik versions >= v2.8.2 through <= v2.11.55 and >= v3.0.0 through <= v3.7.11 do not apply the entryPoints.<name>.transport.respondingTimeouts settings (notably readTimeout, enabled by default at 60s) 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, an unauthenticated remote client can trickle request body bytes and hold a request open indefinitely.
- CVE-2026-88007Critical
Traefik (open source HTTP reverse proxy and load balancer) from 2.11.0 until 2.11.57 and 3.7.13 has an HTTP/3 issue: ConnContext does not call service.AddTransportOnContext, so kerberosRoundTripper uses a shared backend transport instead of one dedicated to each frontend connection. With HTTP/3 enabled, a backend using connection-bound NTLM or Negotiate authentication, and backend keep-alive, an unrelated client can reuse a backend connection authenticated for a victim, read victim-only data, and act as that victim without the victim credentials.
- CVE-2026-85595Critical
Traefik versions before v2.11.55 and versions v3.0.0 through v3.7.10 contain an authentication bypass vulnerability in the digestAuth middleware where unknown usernames receive an empty secret instead of rejection. Attackers can compute a valid digest response using the empty secret and arbitrary credentials to bypass authentication on any digestAuth-protected route without a valid username or password.
- CVE-2026-54763Critical
In Traefik prior to versions v2.11.51, v3.6.22, and v3.7.6, the BasicAuth, DigestAuth, and ForwardAuth middlewares fail to strip underscore-variant identity headers that backends normalize to dashed forms. An attacker can inject such a header to spoof identity or bypass authorization.
Original NVD description (English source)
Traefik is a HTTP reverse proxy and load balancer. In versions >= v3.7.0 and <= v3.7.11, the Kubernetes ingress-nginx provider mishandles Ingresses that carry both an authentication annotation and the nginx.ingress.kubernetes.io/from-to-www-redirect annotation. For such Ingresses the provider creates an additional 'sibling' router that matches on the host alone, carries only the RedirectRegex middleware, and still points at the parent router's protected backend service. Because RedirectRegex is not a terminal handler, a request its pattern does not match is forwarded to the backend, and because the redirect pattern only accepts a numeric port while Traefik's host matcher canonicalizes the authority via net.SplitHostPort, a request with a non-numeric or empty port (for example 'Host: www.example.com:x') selects the sibling router, misses the redirect, and is proxied to the protected backend with none of the Ingress's annotation-derived middlewares applied. This discards not only authentication (e.g. BasicAuth) but every annotation-derived middleware, including source-IP allowlisting. Traefik v2 and v3 releases before v3.7.0 are not affected. The issue is fixed in v3.7.12.