CVE-2026-44373: Nitro Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5w89-w975-hf9q",
  "modified" : "2026-05-14T20:42:49Z",
  "published" : "2026-05-06T23:01:27Z",
  "aliases" : [ "CVE-2026-44373" ],
  "summary" : "Nitro has a proxy scope bypass via percent-encoded path traversal in `routeRules`",
  "details" : "A proxy route rule like:\n\n```ts\nrouteRules: {\n  \"/api/orders/**\": { proxy: { to: \"http://upstream/orders/**\" } }\n}\n```\n\nis intended to limit the proxy to URLs under `/api/orders/`. Before the patch, an attacker could bypass that scope by sending percent-encoded path traversal (`..%2f`) in the URL, causing Nitro to forward a request that the upstream resolved outside the configured scope. Example exploit:\n\n```\nGET /api/orders/..%2fadmin%2fconfig.json\n```\n\nNitro sees `..%2f` as opaque characters at match time, the `/api/orders/**` rule matched, and the raw path was forwarded to the upstream as `/orders/..%2fadmin/config.json`. An upstream that decodes `%2F` to  `/` then resolved `..` and can serve `/admin/config.json` outside the intended scope.\n\n### Are you affected?\n\nUsers may be affected if **ALL** of the following are true:\n\n1. Their project uses Nitro's `routeRules` with a `proxy` entry (`{ proxy: { to: \"...\" } }`).\n2. The proxy `to` value uses a `/**` wildcard suffix to forward sub-paths.\n3. The **upstream** behind the proxy decodes `%2F` as `/` before routing or filesystem lookup.\n4. Proxy route rules are _not_ handled natively at CDN (nitro v3 and vercel)\n\nWhether the bypass actually leaks data depends on the upstream. Modern JS frameworks keep `%2F` opaque per RFC 3986 and are safe by construction. \n\n- **Safe examples:** H3 v2, Express v5, Hono v4 — modern JS frameworks keep `%2F` opaque per RFC 3986.\n- **Vulnerable examples:** naive imlementations that decodes the URL, static file servers, CGI dispatchers, Python `os.path`-based routing, anything sitting behind another layer that decodes `%2F` (common in microservice meshes).\n\n## Impact\n\nAny HTTP path reachable from the Nitro server to the upstream could be requested, regardless of the configured `/**` scope. In typical deployments (API gateway, BFF, microservice proxy) this could expose internal admin endpoints, secrets endpoints, or other services the developer believed the scope rule fenced off.\n\n## Patched versions\n\nUpgrade to one of:\n\n- [2.13.4](https://github.com/nitrojs/nitro/releases/tag/v2.13.4) or later (https://github.com/nitrojs/nitro/pull/4223) \n- [3.0.260429-beta](https://github.com/nitrojs/nitro/releases/tag/v3.0.260429-beta) or later (https://github.com/nitrojs/nitro/pull/4222)\n\nThe fix canonicalizes the incoming pathname before building the upstream URL and rejects requests with `400 Bad Request` if the resolved path would escape the rule's base. The bytes forwarded upstream are unchanged when the request is allowed.\n\n> Note: the fix assumes the upstream does not double-decode percent-encoding. If your upstream decodes twice (`%252F → %2F → /`), it remains your responsibility to harden it. **Single-decode is standard**.\n\n## Credits\n\nReported by [@mHe4am](https://github.com/mHe4am) ([@he4am on HackerOne](https://hackerone.com/he4am)) via the [Vercel Open Source](https://hackerone.com/vercel-open-source?type=team) program.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "nitro"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.0.260429-beta"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "nitropack"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.13.4"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/nitrojs/nitro/security/advisories/GHSA-5w89-w975-hf9q"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-44373"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nitrojs/nitro/pull/4222"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nitrojs/nitro/pull/4223"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/nitrojs/nitro"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nitrojs/nitro/releases/tag/v2.13.4"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nitrojs/nitro/releases/tag/v3.0.260429-beta"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-06T23:01:27Z",
    "nvd_published_at" : "2026-05-13T21:16:48Z"
  }
}