CVE-2026-102992: piscina: Prototype-pollution gadget in ThreadPool.options allows RCE via execArgv / loadBalancer / env

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 0.4%, percentile 37: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 37% 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 piscina (npm) >= 5.0.0, < 5.3.2, fixed in 5.3.2; piscina (npm) < 4.9.4, fixed in 4.9.4; piscina (npm) >= 6.0.0-rc.1, < 6.0.0-rc.5, fixed in 6.0.0-rc.5. Check your lockfile, including transitive dependencies.

What it is

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.

From the GitHub advisory

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:

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.

Weakness type: CWE-1321.

Product: piscina (npm) · Assigned by: GitHub_M · Published: 2026-09-30

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: high (needs special conditions)
• 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): 0.43% probability of exploitation activity in the next 30 days; percentile 37.

Timeline

• 2026-09-30 — CVE record last updated
• 2026-09-30 — CVE record published by GitHub_M
• 2026-10-01 — GitHub-reviewed advisory GHSA-67c8-pqhq-4rmx 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-67c8-pqhq-4rmx github.com
2. CVE.org record CVE-2026-102992 cve.org
3. NVD entry CVE-2026-102992 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
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3. github.com github.com
4. github.com github.com
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7. github.com github.com
8. github.com github.com

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