A prototype‑pollution flaw in the toml-node parser allows an attacker to craft a TOML path that includes __proto__ in multiple places. Because the library’s internal path tracking desynchronizes from the object assignment, keys such as __proto__ are written to Object.prototype and Number.prototype. This corrupts the JavaScript runtime’s prototype chain, allowing injected properties to be visible anywhere in the Node.js process. The vulnerability can lead to denial of service, logic or authorization bypass, and can enable remote code execution if the application contains a gadget that allows the attacker to invoke the poisoned prototype methods.

The affected product is the BinaryMuse toml-node library. Any release earlier than 4.1.2 is vulnerable; this includes all 4.1.1 versions and older. Applications that depend on these versions and parse untrusted TOML data are impacted.

The CVSS score of 8.2 marks this issue as high severity, and the EPSS score is currently unavailable. The vulnerability is not listed in the CISA KEV catalog. An attacker can exploit the flaw by providing malicious TOML input to an application that uses the vulnerable parse routine. Once injected, the poisoned prototype can persist throughout the Node.js process, enabling indirect exploitation and potentially remote code execution if a suitable gadget exists. The lack of an EPSS score does not diminish the high functional impact of the flaw.