Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution) vulnerability in Mozilla Convict.
This allows an attacker to inject attributes that are used in other components, or to override existing attributes with ones that have incompatible type, which may lead to a crash.
The main use case of Convict is for handling server-side configurations written by the admins owning the servers, and not random users. So its unlikely that an admin would deliberately sabotage their own server. Still, a situation can happen where an admin not knowledgeable about JavaScript could be tricked by an attacker into writing the malicious JavaScript code into some config files.
This issue affects Convict: before 6.2.4.
The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.
By adding or modifying attributes of an object prototype, it is possible to create attributes that exist on every object, or replace critical attributes with malicious ones. This can be problematic if the product depends on existence or non-existence of certain attributes, or uses pre-defined attributes of object prototype (such as hasOwnProperty, toString or valueOf). This weakness is usually exploited by using a special attribute of objects called proto, constructor or prototype. Such attributes give access to the object prototype. This weakness is often found in code that assigns object attributes based on user input, or merges or clones objects recursively.