CVE-2026-104848: Tinypool: Prototype Pollution gadget in worker options leads to Remote Code Execution

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.5%, percentile 42: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 42% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes tinypool (npm) <= 2.1.0, fixed in 2.1.1. Check your lockfile, including transitive dependencies.

What it is

Tinypool is a minimal Node.js worker thread pool implementation. Prior to 2.1.1, Tinypool constructs ThreadPool.options from a normal options object and reads the execArgv and env worker options in dist/index.js, allowing values inherited from a polluted Object.prototype to be copied into own properties and passed to workerthreads.Worker. An attacker who can first pollute either property can cause each newly spawned worker to load attacker-selected JavaScript through command-line preload arguments or NODEOPTIONS, resulting in code execution with the host process's privileges and possible access to CI secrets, signing material, or build artifacts. This issue is fixed in version 2.1.1.

From the GitHub advisory

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 workerthreads.Worker.

Node 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.

Two keys reach code execution:

1. execArgv — polluting Object.prototype.execArgv = ['--require', '/path/to/attacker.js'] causes every pool worker to load the attacker's script. 2. env — polluting Object.prototype.env = { NODEOPTIONS: '--require /path/to/attacker.js' } achieves the same via environment injection.

Root cause

Weakness type: CWE-1321.

Product: tinypool (npm) · Assigned by: GitHub_M · Published: 2026-10-02

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: present (depends on deployment conditions)
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.50% probability of exploitation activity in the next 30 days; percentile 42.

Timeline

• 2026-10-02 — CVE record last updated
• 2026-10-02 — CVE record published by GitHub_M
• 2026-10-05 — GitHub-reviewed advisory GHSA-5gmw-xhrv-c9v3 published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-5gmw-xhrv-c9v3 github.com
2. CVE.org record CVE-2026-104848 cve.org
3. NVD entry CVE-2026-104848 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com

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