CVE-2026-29054

Traefik is an HTTP reverse proxy and load balancer. From version 2.11.9 to 2.11.37 and from version 3.1.3 to 3.6.8, there is a potential vulnerability in Traefik managing the Connection header with X-Forwarded headers. When Traefik processes HTTP/1.1 requests, the protection put in place to prevent the removal of Traefik-managed X-Forwarded headers (such as X-Real-Ip, X-Forwarded-Host, X-Forwarded-Port, etc.) via the Connection header does not handle case sensitivity correctly. The Connection tokens are compared case-sensitively against the protected header names, but the actual header deletion operates case-insensitively. As a result, a remote unauthenticated client can use lowercase Connection tokens (e.g. Connection: x-real-ip) to bypass the protection and trigger the removal of Traefik-managed forwarded identity headers. This issue has been patched in versions 2.11.38 and 3.6.9.

Traefik is an HTTP reverse proxy and load balancer. From version 2.11.9 to 2.11.37 and from version 3.1.3 to 3.6.8, there is a potential vulnerability in Traefik managing the Connection header with X-Forwarded headers. When Traefik processes HTTP/1.1 requests, the protection put in place to prevent the removal of Traefik-managed X-Forwarded headers (such as X-Real-Ip, X-Forwarded-Host, X-Forwarded-Port, etc.) via the Connection header does not handle case sensitivity correctly. The Connection tokens are compared case-sensitively against the protected header names, but the actual header deletion operates case-insensitively. As a result, a remote unauthenticated client can use lowercase Connection tokens (e.g. Connection: x-real-ip) to bypass the protection and trigger the removal of Traefik-managed forwarded identity headers. This issue has been patched in versions 2.11.38 and 3.6.9.

traefik CVE-2024-45410 fix bypass: lowercase `Connection` tokens can delete traefik-managed forwarded identity headers (for example, `X-Real-Ip`) in github.com/traefik/traefik

## Impact There is a potential vulnerability in Traefik managing the `Connection` header with `X-Forwarded` headers. When Traefik processes HTTP/1.1 requests, the protection put in place to prevent the removal of Traefik-managed `X-Forwarded` headers (such as `X-Real-Ip`, `X-Forwarded-Host`, `X-Forwarded-Port`, etc.) via the `Connection` header does not handle case sensitivity correctly. The `Connection` tokens are compared case-sensitively against the protected header names, but the actual header deletion operates case-insensitively. As a result, a remote unauthenticated client can use lowercase `Connection` tokens (e.g. `Connection: x-real-ip`) to bypass the protection and trigger the removal of Traefik-managed forwarded identity headers. This is a bypass of the fix for [CVE-2024-45410](https://github.com/traefik/traefik/security/advisories/GHSA-62c8-mh53-4cqv). Depending on the deployment, the impact may be higher if downstream services rely on these headers (such as `X-Real-Ip` or `X-Forwarded-*`) for authentication, authorization, routing, or scheme decisions. ## Patches - https://github.com/traefik/traefik/releases/tag/v2.11.38 - https://github.com/traefik/traefik/releases/tag/v3.6.9 ## Workarounds No workaround available. ## For more information If there are any questions or comments about this advisory, please [open an issue](https://github.com/traefik/traefik/issues). --- <details> <summary>Original Description</summary> Traefik's XForwarded middleware (removeConnectionHeaders) tries to prevent clients from using the Connection header to strip trusted X-Forwarded-* headers, but the protection compares the Connection tokens case-sensitively while the deletion is case-insensitive. As a result, a remote unauthenticated client can send a lowercase token like Connection: x-real-ip and still trigger deletion of traefik-managed X-Real-Ip (and similarly named headers in the managed list). This can cause downstream routing, scheme, and header-based authn/authz decisions to be evaluated with missing trusted forwarding identity headers. ### Severity CRITICAL Rationale: the PoC demonstrates an end-to-end access control bypass pattern when a downstream service uses proxy-provided identity headers (for example, X-Real-Ip) for IP allowlists or trust decisions. A remote unauthenticated client can strip the traefik-managed identity header via a lowercase Connection token, causing the downstream service to evaluate the request without the expected header signal. ### Relevant Links - Repository: https://github.com/traefik/traefik - Pinned commit: a4a91344edcdd6276c1b766ca19ee3f0e346480f - Callsite (pinned): https://github.com/traefik/traefik/blob/a4a91344edcdd6276c1b766ca19ee3f0e346480f/pkg/middlewares/forwardedheaders/forwarded_header.go#L225 ### Vulnerability Details #### Root Cause removeConnectionHeaders uses a case-sensitive membership check for protected header names when inspecting Connection tokens, but it deletes headers via net/http which treats header names case-insensitively. A lowercase token bypasses the protection check and still triggers deletion. #### Attacker Control / Attack Path Remote unauthenticated HTTP client (untrusted IP) sends Connection: x-real-ip, and Traefik deletes the generated X-Real-Ip header. ### Proof of Concept The attached poc.zip contains a deterministic, make-based integration PoC with a canonical run and a negative control. Canonical (vulnerable): unzip poc.zip -d poc cd poc make test Output contains: [CALLSITE_HIT]: pkg/middlewares/forwardedheaders/forwarded_header.go:225 [PROOF_MARKER]: downstream_admin_bypass=1 x_real_ip_present=0 Control (same env, no lowercase token): unzip poc.zip -d poc cd poc make test Output contains: [CALLSITE_HIT]: pkg/middlewares/forwardedheaders/forwarded_header.go:225 [NC_MARKER]: downstream_admin_bypass=0 x_real_ip_present=1 Expected: Connection tokens are handled case-insensitively and protected identity headers (for example, X-Real-Ip and X-Forwarded-*) are not deleted due to client-supplied Connection options (regardless of token casing). Actual: Lowercase Connection tokens bypass the protection check and still trigger deletion of traefik-managed identity headers (for example, X-Real-Ip). ### Recommended Fix - Case-fold (or otherwise canonicalize) Connection header tokens before comparing them against protected header names. - Add a regression test covering lowercase tokens (for example, Connection: x-real-ip). Fix accepted when: a request with Connection: x-real-ip does not cause deletion of traefik-managed X-Real-Ip, and a regression test covers this behavior. </details>

Traefik es un proxy inverso HTTP y un equilibrador de carga. Desde la versión 2.11.9 hasta la 2.11.37 y desde la versión 3.1.3 hasta la 3.6.8, existe una potencial vulnerabilidad en Traefik al gestionar el encabezado Connection con los encabezados X-Forwarded. Cuando Traefik procesa solicitudes HTTP/1.1, la protección implementada para evitar la eliminación de los encabezados X-Forwarded gestionados por Traefik (como X-Real-Ip, X-Forwarded-Host, X-Forwarded-Port, etc.) a través del encabezado Connection no maneja correctamente la distinción entre mayúsculas y minúsculas. Los tokens de Connection se comparan con distinción entre mayúsculas y minúsculas con los nombres de los encabezados protegidos, pero la eliminación real del encabezado opera sin distinción entre mayúsculas y minúsculas. Como resultado, un cliente remoto no autenticado puede usar tokens de Connection en minúsculas (p. ej., Connection: x-real-ip) para eludir la protección y activar la eliminación de los encabezados de identidad reenviados gestionados por Traefik. Este problema ha sido parcheado en las versiones 2.11.38 y 3.6.9.