CVE-2021-44906

Originally from: https://github.com/Marynk/JavaScript-vulnerability-detection/blob/main/minimist%20PoC.zip

Run

npm run hack

And you will see the any function's done property is changed to true. The explanation of command line node index.js --_.concat.constructor.prototype.done true:

• -- is the hypen mark normally used in command line arguments.
• _ is the built in key in minimist: https://github.com/minimistjs/minimist/blob/v1.2.5/index.js#L37
• .concat.constructor.prototype.done true will set _.concat.constructor.prototype.done to true. Because _.concat.constructor is a Function type, all Function's prototype will be added by a property called done.

The reason why the prototype chain is this long is that in the previous fixes, the developer banned __proto__, Arrary.prototype, Object.prototype, Number.prototype and String.prototype. So we have to use constructor who has prototype property and which is not blacklisted.

Another example is:

npm run hack2

However, in the above two example, we can only tamper values but not functions' definition.

Cause

In the fix for CVE-2020-7598 (1.2.2), and in 1.2.3 the developer already fixed some vulnerability by checking __proto__, Arrary.prototype, Object.prototype, Number.prototype, String.prototype, but they forgot to check Function.prototye. This is why this exploit can only affect the property of Function. For the fix of this CVE, the developer checked the Function.prototype as well as constructor: https://github.com/minimistjs/minimist/blob/v1.2.6/index.js#L73