GHSA-92mv-8f8w-wq52: traefik CVE-2024-45410 fix bypass: lowercase `Connection` tokens can delete traefik-managed forwarded identity headers (for example, `X-Real-Ip`)
ImpactThere 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.Patcheshttps://github.com/traefik/traefik/releases/tag/v2.11.38https://github.com/traefik/traefik/releases/tag/v3.6.9WorkaroundsNo workaround available.For more informationIf there are any questions or comments about this advisory, please [open an issue](https://github.com/traefik/traefik/issues).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.SeverityCRITICALRationale: 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 LinksRepository: https://github.com/traefik/traefikPinned commit: a4a91344edcdd6276c1b766ca19ee3f0e346480fCallsite (pinned): https://github.com/traefik/traefik/blob/a4a91344edcdd6276c1b766ca19ee3f0e346480f/pkg/middlewares/forwardedheaders/forwarded_header.go#L225Vulnerability DetailsRoot CauseremoveConnectionHeaders 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 PathRemote unauthenticated HTTP client (untrusted IP) sends Connection: x-real-ip, and Traefik deletes the generated X-Real-Ip header.Proof of ConceptThe attached poc.zip contains a deterministic, make-based integration PoC with a canonical run and a negative control.Canonical (vulnerable):Output contains:Control (same env, no lowercase token):Output contains: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 FixCase-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.
CVSS v3.1: 7.5