CVE-2026-104849: Tinypool: Prototype Pollution Gadget to RCE in run() options

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.

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().