CVE-2026-54737: @phun-ky/defaults-deep Has a Prototype Pollution issue via Unsafe Recursive Property Merging

A prototype pollution vulnerability exists in @phun-ky/defaults-deep prior to version 2.0.5.

The library recursively merged user-supplied objects without filtering unsafe property names such as __proto__, constructor, and prototype. An attacker able to supply crafted input could cause properties to be written to Object.prototype, resulting in prototype pollution affecting all objects within the running process.

Applications that pass untrusted input to defaultsDeep() may be impacted. Depending on how the application uses merged objects, this could lead to unexpected behavior, logic bypasses, denial of service, or other security issues.