The NPM package micromatch prior to version 4.0.8 is vulnerable to Regular Expression Denial of Service (ReDoS). The vulnerability occurs in micromatch.braces() in index.js because the pattern .* will greedily match anything. By passing a malicious payload, the pattern matching will keep backtracking to the input while it doesn't find the closing bracket. As the input size increases, the consumption time will also increase until it causes the application to hang or slow down. There was a merged fix but further testing shows the issue persisted prior to https://github.com/micromatch/micromatch/pull/266. This issue should be mitigated by using a safe pattern that won't start backtracking the regular expression due to greedy matching.

The NPM package braces fails to limit the number of characters it can handle, which could lead to Memory Exhaustion. In lib/parse.js, if a malicious user sends "imbalanced braces" as input, the parsing will enter a loop, which will cause the program to start allocating heap memory without freeing it at any moment of the loop. Eventually, the JavaScript heap limit is reached, and the program will crash.

Summary

The arrayLimit option in qs does not enforce limits for bracket notation (a[]=1&a[]=2), allowing attackers to cause denial-of-service via memory exhaustion. Applications using arrayLimit for DoS protection are vulnerable.

Details

The arrayLimit option only checks limits for indexed notation (a[0]=1&a[1]=2) but completely bypasses it for bracket notation (a[]=1&a[]=2).

Vulnerable code (lib/parse.js:159-162):

if (root === '[]' && options.parseArrays) {
    obj = utils.combine([], leaf);  // No arrayLimit check
}

Working code (lib/parse.js:175):

else if (index <= options.arrayLimit) {  // Limit checked here
    obj = [];
    obj[index] = leaf;
}

The bracket notation handler at line 159 uses utils.combine([], leaf) without validating against options.arrayLimit, while indexed notation at line 175 checks index <= options.arrayLimit before creating arrays.

PoC

Test 1 - Basic bypass:

npm install qs

const qs = require('qs');
const result = qs.parse('a[]=1&a[]=2&a[]=3&a[]=4&a[]=5&a[]=6', { arrayLimit: 5 });
console.log(result.a.length);  // Output: 6 (should be max 5)

Test 2 - DoS demonstration:

const qs = require('qs');
const attack = 'a[]=' + Array(10000).fill('x').join('&a[]=');
const result = qs.parse(attack, { arrayLimit: 100 });
console.log(result.a.length);  // Output: 10000 (should be max 100)

Configuration:

• arrayLimit: 5 (test 1) or arrayLimit: 100 (test 2)
• Use bracket notation: a[]=value (not indexed a[0]=value)

Impact

Denial of Service via memory exhaustion. Affects applications using qs.parse() with user-controlled input and arrayLimit for protection.

Attack scenario:

1. Attacker sends HTTP request: GET /api/search?filters[]=x&filters[]=x&...&filters[]=x (100,000+ times)
2. Application parses with qs.parse(query, { arrayLimit: 100 })
3. qs ignores limit, parses all 100,000 elements into array
4. Server memory exhausted → application crashes or becomes unresponsive
5. Service unavailable for all users

Real-world impact:

• Single malicious request can crash server
• No authentication required
• Easy to automate and scale
• Affects any endpoint parsing query strings with bracket notation

Suggested Fix

Add arrayLimit validation to the bracket notation handler. The code already calculates currentArrayLength at line 147-151, but it's not used in the bracket notation handler at line 159.

Current code (lib/parse.js:159-162):

if (root === '[]' && options.parseArrays) {
    obj = options.allowEmptyArrays && (leaf === '' || (options.strictNullHandling && leaf === null))
        ? []
        : utils.combine([], leaf);  // No arrayLimit check
}

Fixed code:

if (root === '[]' && options.parseArrays) {
    // Use currentArrayLength already calculated at line 147-151
    if (options.throwOnLimitExceeded && currentArrayLength >= options.arrayLimit) {
        throw new RangeError('Array limit exceeded. Only ' + options.arrayLimit + ' element' + (options.arrayLimit === 1 ? '' : 's') + ' allowed in an array.');
    }
    
    // If limit exceeded and not throwing, convert to object (consistent with indexed notation behavior)
    if (currentArrayLength >= options.arrayLimit) {
        obj = options.plainObjects ? { __proto__: null } : {};
        obj[currentArrayLength] = leaf;
    } else {
        obj = options.allowEmptyArrays && (leaf === '' || (options.strictNullHandling && leaf === null))
            ? []
            : utils.combine([], leaf);
    }
}

This makes bracket notation behaviour consistent with indexed notation, enforcing arrayLimit and converting to object when limit is exceeded (per README documentation).

A specially crafted URL with an '@' sign but empty user info and no hostname, when parsed with url-parse, url-parse will return the incorrect href. In particular,

parse(\"http://@/127.0.0.1\")

Will return:

{
 slashes: true,
 protocol: 'http:',
 hash: '',
 query: '',
 pathname: '/127.0.0.1',
 auth: '',
 host: '',
 port: '',
 hostname: '',
 password: '',
 username: '',
 origin: 'null',
 href: 'http:///127.0.0.1'
 }

If the 'hostname' or 'origin' attributes of the output from url-parse are used in security decisions and the final 'href' attribute of the output is then used to make a request, the decision may be incorrect.

url-parse before 1.5.0 mishandles certain uses of backslash such as http:/ and interprets the URI as a relative path.

url-parse prior to version 1.5.8 is vulnerable to Authorization Bypass Through User-Controlled Key.

Overview

Affected versions of npm url-parse are vulnerable to URL Redirection to Untrusted Site.

Impact

Depending on library usage and attacker intent, impacts may include allow/block list bypasses, SSRF attacks, open redirects, or other undesired behavior.

Leading control characters in a URL are not stripped when passed into url-parse. This can cause input URLs to be mistakenly be interpreted as a relative URL without a hostname and protocol, while the WHATWG URL parser will trim control characters and treat it as an absolute URL.

If url-parse is used in security decisions involving the hostname / protocol, and the input URL is used in a client which uses the WHATWG URL parser, the decision may be incorrect.

This can also lead to a cross-site scripting (XSS) vulnerability if url-parse is used to check for the javascript: protocol in URLs. See following example:

const parse = require('url-parse')
const express = require('express')
const app = express()
const port = 3000

url = parse(\"\\bjavascript:alert(1)\")

console.log(url)

app.get('/', (req, res) => {
 if (url.protocol !== \"javascript:\") {res.send(\"<a href=\\'\" + url.href + \"\\'>CLICK ME!</a>\")}
 })

app.listen(port, () => {
 console.log(`Example app listening on port ${port}`)
 })

Authorization Bypass Through User-Controlled Key in NPM url-parse prior to 1.5.6.