piscina: Prototype-pollution gadget in ThreadPool.options allows RCE via execArgv / loadBalancer / env

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piscina is a node.js worker pool implementation. Prior to 4.9.4, 5.3.2, and 6.0.0-rc.5, Piscina stores ThreadPool.options in src/index.ts as a plain object that inherits from Object.prototype. Applications with a separate prototype-pollution primitive can therefore supply inherited values for security-sensitive options that do not have own defaults. An inherited execArgv value is passed to the Node.js Worker constructor and can preload attacker-controlled code in worker threads, an inherited loadBalancer function can execute during task scheduling, and inherited env values can alter worker environments. This issue is fixed in versions 4.9.4, 5.3.2, and 6.0.0-rc.5.

Source published

30 Sep 2026 19:50:18 UTC

Source modified

30 Sep 2026 20:47:49 UTC

Saved here

23 Oct 2026 15:48:27 UTC

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CVE Program Terms of Use

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Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 4.0 · 9.2 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

piscina is a node.js worker pool implementation. Prior to 4.9.4, 5.3.2, and 6.0.0-rc.5, Piscina stores ThreadPool.options in src/index.ts as a plain object that inherits from Object.prototype. Applications with a separate prototype-pollution primitive can therefore supply inherited values for security-sensitive options that do not have own defaults. An inherited execArgv value is passed to the Node.js Worker constructor and can preload attacker-controlled code in worker threads, an inherited loadBalancer function can execute during task scheduling, and inherited env values can alter worker environments. This issue is fixed in versions 4.9.4, 5.3.2, and 6.0.0-rc.5.

Source published

Sep 30, 2026, 7:50:18 PM (timezone not stated)

Source modified

Sep 30, 2026, 8:47:49 PM (timezone not stated)

Saved here

11 Nov 2026 05:29:45 UTC

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ENISA EUVD · source terms and attribution apply

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Source: euvd · ENISA EUVD · source terms and attribution apply. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

EUVD CVSS 4.0 · 9.2 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

piscina is a node.js worker pool implementation. Prior to 4.9.4, 5.3.2, and 6.0.0-rc.5, Piscina stores ThreadPool.options in src/index.ts as a plain object that inherits from Object.prototype. Applications with a separate prototype-pollution primitive can therefore supply inherited values for security-sensitive options that do not have own defaults. An inherited execArgv value is passed to the Node.js Worker constructor and can preload attacker-controlled code in worker threads, an inherited loadBalancer function can execute during task scheduling, and inherited env values can alter worker environments. This issue is fixed in versions 4.9.4, 5.3.2, and 6.0.0-rc.5.

Source published

30 Sep 2026 20:17:27 UTC

Source modified

30 Sep 2026 21:17:06 UTC

Saved here

25 Oct 2026 04:17:29 UTC

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NIST NVD usage terms; underlying source attribution retained

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Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 4.0 · [email protected] · Secondary · 9.2 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

### Summary A prototype-pollution gadget in `ThreadPool.options` allows an attacker who can pollute `Object.prototype` to execute arbitrary code in Piscina worker threads, invoke arbitrary functions during task scheduling, or inject environment variables into workers. The root cause is that `ThreadPool.options` is created as a plain object inheriting from `Object.prototype`, so any option without an explicit default in `kDefaultOptions` can be supplied via the prototype chain. ### Details In `src/index.ts` the `ThreadPool` constructor builds the resolved options object as a plain object: ```ts this.options = { ...kDefaultOptions, ...options, filename, maxQueue: 0 } ``` Because this object has `Object.prototype` as its prototype, reads for properties that are not own properties of the object and are not present in `kDefaultOptions` fall back to `Object.prototype`. This means a prototype-pollution primitive (e.g. from a vulnerable `merge()` or `JSON.parse` merge elsewhere in the application) can inject values for `execArgv`, `env`, `loadBalancer`, `argv`, `workerData`, `resourceLimits`, `niceIncrement`, `closeTimeout`, `recordTiming`, `stricterFIFO`, `workerHistogram`, and `trackUnmanagedFds`. The most serious gadget is `execArgv`, which is passed directly to `new Worker(..., { execArgv })`. An attacker can set `Object.prototype.execArgv = ['--require', '/tmp/attacker.js']`, causing every worker to preload and execute the attacker-controlled module on startup. This issue survived the fix for **GHSA-x9g3-xrwr-cwfg / CVE-2026-55388** ("Prototype Pollution Gadget → RCE via inherited options.filename"). That advisory hardened the `Piscina` constructor's `filename` read and `run()`'s `filename`/`name` reads, but `ThreadPool.options` itself was not created with a null prototype. The same class of attack is therefore still possible against any option without an explicit default in `kDefaultOptions`. ### PoC ```js import { resolve } from 'node:path' import Piscina from 'piscina' Object.prototype.execArgv = ['--require', '/tmp/attacker.js'] const pool = new Piscina({ filename: resolve(import.meta.dirname, 'worker.js'), minThreads: 1, maxThreads: 1, }) await pool.run(1) ``` `/tmp/attacker.js` is executed in the worker on startup. A full reproduction repository with `execArgv`, `loadBalancer`, and `env` vectors is available at https://github.com/Fcmam5/piscina-pp-poc. ### Impact - **Remote Code Execution**: via `execArgv` (arbitrary `--require` module preloaded in every worker on spawn). - **Arbitrary code execution in the main thread**: via `loadBalancer`, an attacker-supplied function that is called during task scheduling. - **Environment/CLI option injection**: via `env`, which is passed to each worker constructor. - **Denial of Service / unexpected behavior**: via other reachable options such as `workerData`, `resourceLimits`, `niceIncrement`, `closeTimeout`, `recordTiming`, etc. Anyone using Piscina in an application where `Object.prototype` can be polluted (e.g. through a dependency with a prototype-pollution vulnerability) is impacted.

Source published

1 Oct 2026 15:03:33 UTC

Source modified

1 Oct 2026 15:15:09 UTC

Saved here

24 Oct 2026 13:17:17 UTC

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GitHub Advisory Database · CC-BY-4.0

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Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS_V4 · CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Publisher rating · CRITICAL