Medium

qs's arrayLimit bypass in its bracket notation allows DoS via memory exhaustion

Disclosed: 30.12.2025
Updated: 11.10.2026 10:22

Summary

The arrayLimit option in qs did not enforce limits for bracket notation (a[]=1&a[]=2), only for indexed notation (a[0]=1). This is a consistency bug; arrayLimit should apply uniformly across all array notations.

Note: The default parameterLimit of 1000 effectively mitigates the DoS scenario originally described. With default options, bracket notation cannot produce arrays larger than parameterLimit regardless of arrayLimit, because each a[]=value consumes one parameter slot. The severity has been reduced accordingly.

Details

The arrayLimit option only checked limits for indexed notation (a[0]=1&a[1]=2) but did not enforce 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

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)

Note on parameterLimit interaction: The original advisory's "DoS demonstration" claimed a length of 10,000, but parameterLimit (default: 1000) caps parsing to 1,000 parameters. With default options, the actual output is 1,000, not 10,000.

Impact

Consistency bug in arrayLimit enforcement. With default parameterLimit, the practical DoS risk is negligible since parameterLimit already caps the total number of parsed parameters (and thus array elements from bracket notation). The risk increases only when parameterLimit is explicitly set to a very high value.

Affected software

Click a technology to see all vulnerabilities affecting it.

Platform	Package	Vulnerable versions	Fixed in
npm package	qs	< 6.14.1	6.14.1

References

CVSS score 3.7/10

CVSS vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
Weakness (CWE): CWE-20
Platform: npm
Package: qs
Disclosed: 30.12.2025
Updated: 11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-6rw7-vpxm-498p - CC BY 4.0

Vulnerability history: qs

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (9) in the archive

Total entries: 9
First → latest: 10.2017 09.2026
Without a fix: 0
Exploited in attacks: 0

Severity breakdown

High 4
Medium 4
Low 1

Disclosures per year

2017: 1
2018: 1
2019: 0
2020: 1
2021: 0
2022: 1
2023: 0
2024: 0
2025: 1
2026: 4

30.12.2025

qs's arrayLimit bypass in its bracket notation allows DoS via memory exhaustion this entry

Medium · 3.7 CVE-2025-15284 < 6.14.1 6.14.1
27.11.2022

qs vulnerable to Prototype Pollution

High · 7.5 CVE-2022-24999 >= 6.10.0, < 6.10.3, >= 6.9.0, < 6.9.7, >= 6.8.0, < 6.8.3, >= 6.7.0, < 6.7.3, >= 6.6.0, < 6.6.1, >= 6.5.0, < 6.5.3, >= 6.4.0, < 6.4.1, >= 6.3.0, < 6.3.3, < 6.2.4 6.10.3, 6.9.7, 6.8.3, 6.7.3, 6.6.1, 6.5.3, 6.4.1, 6.3.3, 6.2.4
30.04.2020

Prototype Pollution Protection Bypass in qs

High · 7.5 CVE-2017-1000048 < 6.0.4, >= 6.1.0, < 6.1.2, >= 6.2.0, < 6.2.3, >= 6.3.0, < 6.3.2 6.0.4, 6.1.2, 6.2.3, 6.3.2
09.10.2018

Denial-of-Service Extended Event Loop Blocking in qs

High CVE-2014-10064 < 1.0.0 1.0.0
24.10.2017

Denial-of-Service Memory Exhaustion in qs

High CVE-2014-7191 < 1.0.0 1.0.0

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