Description
Improper Input Validation vulnerability in qs (parse modules) allows HTTP DoS.This issue affects qs: < 6.14.1. SummaryThe 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. DetailsThe 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. PoCTest 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) ImpactDenial of Service via memory exhaustion. Affects applications using qs.parse() with user-controlled input and arrayLimit for protection. Attack scenario: * Attacker sends HTTP request: GET /api/search?filters[]=x&filters[]=x&...&filters[]=x (100,000+ times) * Application parses with qs.parse(query, { arrayLimit: 100 }) * qs ignores limit, parses all 100,000 elements into array * Server memory exhausted → application crashes or becomes unresponsive * 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
Risk Information
cvss3
Base: 7.5
Severity: LOW
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cvss4
Base: 8.7
Severity: LOW
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
