CVE-2026-29054: traefik CVE-2024-45410 fix bypass Lowercase `Connection` Tokens Can Delete Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-92mv-8f8w-wq52",
  "modified" : "2026-03-05T22:37:26Z",
  "published" : "2026-03-04T21:19:08Z",
  "aliases" : [ "CVE-2026-29054" ],
  "summary" : "traefik CVE-2024-45410 fix bypass: lowercase `Connection` tokens can delete traefik-managed forwarded identity headers (for example, `X-Real-Ip`)",
  "details" : "## 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<details>\n<summary>Original Description</summary>\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</details>",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/traefik/traefik/v2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.11.9"
      }, {
        "fixed" : "2.11.38"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.11.37"
    }
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/traefik/traefik/v3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.1.3"
      }, {
        "fixed" : "3.6.9"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.6.8"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/traefik/traefik/security/advisories/GHSA-92mv-8f8w-wq52"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-29054"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/traefik/traefik"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/traefik/traefik/releases/tag/v2.11.38"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/traefik/traefik/releases/tag/v3.6.9"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-178" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-04T21:19:08Z",
    "nvd_published_at" : "2026-03-05T19:16:15Z"
  }
}