FreeScout is a free, self-hosted help desk and shared mailbox. Versions of FreeScout prior to 1.8.139 contain a Prototype Pollution vulnerability in the "/public/js/main.js" source file. The Prototype Pollution arises because the "getQueryParam" Function recursively merges an object containing user-controllable properties into an existing object (For URL Query Parameters Parsing), without first sanitizing the keys. This can allow an attacker to inject a property with a key "__proto__", along with arbitrarily nested properties. The merge operation assigns the nested properties to the "params" object's prototype instead of the target object itself. As a result, the attacker can pollute the prototype with properties containing harmful values, which are then inherited by user-defined objects and subsequently used by the application dangerously. The vulnerability lets an attacker control properties of objects that would otherwise be inaccessible. If the application subsequently handles an attacker-controlled property in an unsafe way, this can potentially be chained with other vulnerabilities like DOM-based XSS, Open Redirection, Cookie Manipulation, Link Manipulation, HTML Injection, etc. Version 1.8.139 contains a patch for the issue.