toml-node is a TOML parser for Node.js and the browser. Prior to 4.1.2, toml.parse() in lib/compiler.js can be tricked by a table path such as a.b.y.__proto__.__proto__, allowing traversal from a scalar value into Number.prototype and Object.prototype. The currentPath tracking value uses both arrays and strings, so valueAssignments records a comma-joined path such as a,b.y while deepRef checks the dot-joined path a.b.y, allowing the duplicate-key guard to miss and attacker-controlled keys to be written to Object.prototype. A table-array prefix-clearing path in addTableArray can also erase guard state before the same __proto__ traversal. Injected properties become visible throughout the Node.js process and can cause denial of service, logic or authorization bypass, or code execution when an application contains a suitable gadget. This issue is fixed in version 4.1.2.

A prototype pollution vulnerability exists in the toml-node TOML parser for Node.js prior to version 4.1.2. The toml.parse() function in lib/compiler.js can be exploited via specially crafted table paths containing __proto__ segments, allowing attackers to traverse into Number.prototype and Object.prototype. A mismatch between how valueAssignments records paths (comma-joined) and how deepRef checks them (dot-joined) causes the duplicate-key guard to be bypassed, enabling attacker-controlled keys to be written to Object.prototype. Additionally, the addTableArray function can erase guard state, enabling a secondary attack vector. Injected properties propagate across the entire Node.js process, potentially enabling denial of service, authorization or logic bypass, or remote code execution if a suitable gadget exists in the application. The vulnerability has been patched in toml-node version 4.1.2.