{ "canonical_id": "traefik--CVE-2026-29054", "system_id": "traefik", "display_name": "Traefik", "category": "servers", "advisory_mode": "server", "title": "traefik CVE-2024-45410 fix bypass: lowercase `Connection` tokens can delete traefik-managed forwarded identity headers (for example, `X-Real-Ip`)", "summary": "## Impact\n\nThere is a potential vulnerability in Traefik managing the `Connection` header with `X-Forwarded` headers.\n\nWhen 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.\n\nThis is a bypass of the fix for [CVE-2024-45410](https://github.com/traefik/traefik/security/advisories/GHSA-62c8-mh53-4cqv).\n\nDepending 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.\n\n## Patches\n\n- https://github.com/traefik/traefik/releases/tag/v2.11.38\n- https://github.com/traefik/traefik/releases/tag/v3.6.9\n\n## Workarounds\n\nNo workaround available.\n\n## For more information\n\nIf there are any questions or comments about this advisory, please [open an issue](https://github.com/traefik/traefik/issues).\n\n---\n\n
\nOriginal Description\n\nTraefik'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.\n\nAs 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).\n\nThis can cause downstream routing, scheme, and header-based authn/authz decisions to be evaluated with missing trusted forwarding identity headers.\n\n### Severity\n\nCRITICAL\n\nRationale: 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.\n\n### Relevant Links\n\n- Repository: https://github.com/traefik/traefik\n- Pinned commit: a4a91344edcdd6276c1b766ca19ee3f0e346480f\n- Callsite (pinned): https://github.com/traefik/traefik/blob/a4a91344edcdd6276c1b766ca19ee3f0e346480f/pkg/middlewares/forwardedheaders/forwarded_header.go#L225\n\n### Vulnerability Details\n\n#### Root Cause\n\nremoveConnectionHeaders 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.\n\n#### Attacker Control / Attack Path\n\nRemote unauthenticated HTTP client (untrusted IP) sends Connection: x-real-ip, and Traefik deletes the generated X-Real-Ip header.\n\n### Proof of Concept\n\nThe attached poc.zip contains a deterministic, make-based integration PoC with a canonical run and a negative control.\n\nCanonical (vulnerable):\n\n unzip poc.zip -d poc\n cd poc\n make test\n\nOutput contains:\n\n [CALLSITE_HIT]: pkg/middlewares/forwardedheaders/forwarded_header.go:225\n [PROOF_MARKER]: downstream_admin_bypass=1 x_real_ip_present=0\n\nControl (same env, no lowercase token):\n\n unzip poc.zip -d poc\n cd poc\n make test\n\nOutput contains:\n\n [CALLSITE_HIT]: pkg/middlewares/forwardedheaders/forwarded_header.go:225\n [NC_MARKER]: downstream_admin_bypass=0 x_real_ip_present=1\n\nExpected: 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).\n\nActual: Lowercase Connection tokens bypass the protection check and still trigger deletion of traefik-managed identity headers (for example, X-Real-Ip).\n\n### Recommended Fix\n\n- Case-fold (or otherwise canonicalize) Connection header tokens before comparing them against protected header names.\n- Add a regression test covering lowercase tokens (for example, Connection: x-real-ip).\n\nFix 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.\n\n
", "published_at": "2026-03-04T21:19:08Z", "updated_at": "2026-03-05T22:46:31.066201Z", "severity": "low", "cvss_score": 3.1, "exploit_status": "unknown", "source_confidence": "official", "official_source_url": "https://github.com/traefik/traefik/security/advisories/GHSA-92mv-8f8w-wq52", "secondary_source_urls": [ "https://nvd.nist.gov/vuln/detail/CVE-2026-29054", "https://github.com/traefik/traefik", "https://github.com/traefik/traefik/releases/tag/v2.11.38", "https://github.com/traefik/traefik/releases/tag/v3.6.9" ], "aliases": [ "CVE-2026-29054", "GHSA-92mv-8f8w-wq52" ], "cve_ids": [ "CVE-2026-29054" ], "ghsa_ids": [ "GHSA-92mv-8f8w-wq52" ], "osv_ids": [ "GHSA-92mv-8f8w-wq52" ], "affected_versions": [ "introduced=2.11.9, fixed<2.11.38", "introduced=3.1.3, fixed<3.6.9" ], "fixed_versions": [ "2.11.38", "3.6.9" ], "package_name": "github.com/traefik/traefik/v3", "render_markdown": false, "case_path": null, "secure_code_topics": [ "proxy-trust-boundary", "request-smuggling-boundary", "token-cookie-storage", "authz-server-side-recheck", "dependency-upgrade-policy" ], "status": "generated", "triage_reasons": [], "verification_status": "triage-manual", "verification_mode": "synthetic", "last_verified_at": null, "last_run_id": null, "evidence_bundle": null, "historical_status": null, "latest_status": null, "browser_evidence": { "required": false, "present": false, "refs": [] }, "repro_profile_id": "authz-bypass-generic", "artifact_mode": "synthetic", "blocked_reason": null, "metadata": { "source_names": [ "OSV Traefik" ], "source_kinds": [ "osv-batch" ], "candidate_count": 1 } }