CVE-2026-104849: Tinypool Remote Code Execution Vulnerability

CRITICAL
Advisory Identifier: GHSA-85c8-ppgw-ccpr
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CWE-1321 CWE-94
Published
Advisory Summary

CVE-2026-104849 is a CRITICAL remote code execution vulnerability (CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')) affecting Tinypool libraries in the npm ecosystem. The issue involves prototype pollution gadget to rce in run() options. Remediation is available by upgrading affected packages to version 2.1.2.

CVE-2026-104849 at a Glance

CVE Identifier CVE-2026-104849
GHSA Identifier GHSA-85c8-ppgw-ccpr
Severity CRITICAL
CVSS v3.1 Base Score N/A
CWE Classification CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Affected Product Tinypool
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-104849

To remediate this vulnerability, upgrade all affected Tinypool dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

tinypool fixed: 2.1.2 
npm install tinypool@2.1.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls tinypool

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-104849, inspect your project dependencies using npm:

npm ls tinypool

Analyze the terminal output to locate any version of Tinypool in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.1.2), your application is affected.

Note: The npm ls tinypool command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution'), where the product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype. In Tinypool, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

`tinypool` is a fork of `piscina` and inherited the same prototype-pollution surface. When `pool.run(task, options)` is called, the `filename` option is read from the provided `options` object. If that object does not have an own `filename` property, the lookup falls through to `Object.prototype`. An attacker who can pollute `Object.prototype.filename` (for example, via a vulnerable `lodash.merge`, `qs.parse`, or similar elsewhere in the application) can make tinypool load and execute an attacker-controlled worker module. This is the tinypool counterpart to the piscina root discovery [GHSA-x9g3-xrwr-cwfg](https://github.com/piscinajs/piscina/security/advisories/GHSA-x9g3-xrwr-cwfg). `pool.run(task)` with no second argument is not affected, because `kDefaultOptions.filename` is `null` and the options object is not user-controlled. The exploit only triggers when the caller passes their own options object to `pool.run()`. ## Impact Arbitrary JavaScript execution in the worker pool. If the application passes attacker-controlled data as the `run()` task and also supplies a `run()` options object, the attacker can redirect execution to a malicious worker that exfiltrates or modifies that data, achieving remote code execution and/or data exfiltration. ## Proof of Concept ```js // legitimate-worker.mjs export default async (task) => ({ by: 'legitimate-worker', processed: task }) // malicious-worker.mjs export default async (task) => ({ by: 'attacker', stolenRequestBody: task }) // main.js import express from "express"; import Tinypool from "tinypool"; import { fileURLToPath } from "node:url"; import path from "node:path"; const __dirname = path.dirname(fileURLToPath(import.meta.url)); // Simulate upstream prototype pollution (lodash merge, qs parse, etc.) Object.prototype.filename = path.join(__dirname, "malicious-worker.mjs"); const pool = new Tinypool({ filename: path.join(__dirname, "legitimate-worker.mjs"), }); express() .use(express.json()) .post("/", async (req, res) => { const ac = new AbortController(); const result = await pool.run(req.body, { signal: ac.signal }); res.json(result); }) .listen(31337); ``` ## Suggested fix Read all user-supplied options from own properties only (`Object.hasOwn` or `Object.prototype.hasOwnProperty.call`) and build the internal `ThreadPool.options` object with a null prototype.

CVE-2026-104849 Affected Tinypool Versions

1 component(s)
Fixed Versions:
2.1.2
Product / Package Ecosystem Affected Versions Fixed Version
tinypool
npm/tinypool
npm
< 2.1.2
2.1.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/tinylibs/tinypool/security/advisories/GHSA-85c8-ppgw-ccpr
NVD — CVE-2026-104849 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-104849
Tinypool Source Repository REPOSITORY
https://github.com/tinylibs/tinypool/pull/135
Security Fix Commit FIX COMMIT
https://github.com/tinylibs/tinypool/commit/f41411a3e23324c674f35a19a3240f7a7c40ffbf
Tinypool Source Repository REPOSITORY
https://github.com/tinylibs/tinypool
Tinypool Release RELEASE
https://github.com/tinylibs/tinypool/releases/tag/v2.1.2

Frequently Asked Questions

What is CVE-2026-104849?
CVE-2026-104849 is a security vulnerability in Tinypool involving Prototype Pollution Gadget to RCE in run() options under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution').
Which Tinypool versions are affected?
Affected versions include releases prior to 2.1.2 across affected packages: tinypool.
What version fixes CVE-2026-104849?
Upgrading to 2.1.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is tinypool affected?
Yes, tinypool is affected in releases prior to 2.1.2. Upgrade your dependency to 2.1.2 or later.
What CWE is associated with CVE-2026-104849?
CVE-2026-104849 is classified under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') (The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.).
How can I check npm dependencies for CVE-2026-104849?
Run the dependency tree command: 'npm ls tinypool'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-85c8-ppgw-ccpr",
  "modified" : "2026-10-05T22:49:52Z",
  "published" : "2026-10-05T22:49:52Z",
  "aliases" : [ "CVE-2026-104849" ],
  "summary" : "Tinypool: Prototype Pollution Gadget to RCE in run() options",
  "details" : "`tinypool` is a fork of `piscina` and inherited the same prototype-pollution surface. When `pool.run(task, options)` is called, the `filename` option is read from the provided `options` object. If that object does not have an own `filename` property, the lookup falls through to `Object.prototype`.\n\nAn attacker who can pollute `Object.prototype.filename` (for example, via a vulnerable `lodash.merge`, `qs.parse`, or similar elsewhere in the application) can make tinypool load and execute an attacker-controlled worker module.\n\nThis is the tinypool counterpart to the piscina root discovery [GHSA-x9g3-xrwr-cwfg](https://github.com/piscinajs/piscina/security/advisories/GHSA-x9g3-xrwr-cwfg).\n\n`pool.run(task)` with no second argument is not affected, because `kDefaultOptions.filename` is `null` and the options object is not user-controlled. The exploit only triggers when the caller passes their own options object to `pool.run()`.\n\n## Impact\n\nArbitrary JavaScript execution in the worker pool. If the application passes attacker-controlled data as the `run()` task and also supplies a `run()` options object, the attacker can redirect execution to a malicious worker that exfiltrates or modifies that data, achieving remote code execution and/or data exfiltration.\n\n## Proof of Concept\n\n```js\n// legitimate-worker.mjs\nexport default async (task) => ({ by: 'legitimate-worker', processed: task })\n\n// malicious-worker.mjs\nexport default async (task) => ({ by: 'attacker', stolenRequestBody: task })\n\n// main.js\nimport express from \"express\";\nimport Tinypool from \"tinypool\";\nimport { fileURLToPath } from \"node:url\";\nimport path from \"node:path\";\n\nconst __dirname = path.dirname(fileURLToPath(import.meta.url));\n\n// Simulate upstream prototype pollution (lodash merge, qs parse, etc.)\nObject.prototype.filename = path.join(__dirname, \"malicious-worker.mjs\");\n\nconst pool = new Tinypool({\n  filename: path.join(__dirname, \"legitimate-worker.mjs\"),\n});\n\nexpress()\n  .use(express.json())\n  .post(\"/\", async (req, res) => {\n    const ac = new AbortController();\n    const result = await pool.run(req.body, { signal: ac.signal });\n    res.json(result);\n  })\n  .listen(31337);\n```\n\n## Suggested fix\n\nRead all user-supplied options from own properties only (`Object.hasOwn` or `Object.prototype.hasOwnProperty.call`) and build the internal `ThreadPool.options` object with a null prototype.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "tinypool"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.1.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/tinylibs/tinypool/security/advisories/GHSA-85c8-ppgw-ccpr"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-104849"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/tinylibs/tinypool/pull/135"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/tinylibs/tinypool/commit/f41411a3e23324c674f35a19a3240f7a7c40ffbf"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/tinylibs/tinypool"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/tinylibs/tinypool/releases/tag/v2.1.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1321", "CWE-94" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-05T22:49:52Z",
    "nvd_published_at" : "2026-10-02T17:17:03Z"
  }
}