Medium

qs array-limit bypass via bracket-key comma parsing

Disclosed: 02.09.2026
Updated: 11.10.2026 10:22

Summary

qs v6.15.3 allows bracket-key input to bypass arrayLimit and throwOnLimitExceeded when comma: true. The input a[]=1,2,3,4 succeeds with arrayLimit: 3, while the equivalent plain-key input is rejected.

Affected version tested:

qs v6.15.3
commit 18d085e919dae70c8f1b200ab99323058edab2c2

Details

parseArrayValue() enforces the comma limit only for flat values. The a[] form is marked non-flat, so its comma-separated value is wrapped after parsing and the inner array is not checked. A single parameter can therefore materialize arbitrarily large arrays.

PoC

const qs = require('qs')
const options = { comma: true, arrayLimit: 3, throwOnLimitExceeded: true }

const result = qs.parse('a[]=1,2,3,4', options)
console.log(result.a[0].length) // 4; expected RangeError

const big = qs.parse('a[]=' + '1,'.repeat(1000000) + '1', { comma: true, arrayLimit: 20 })
console.log(big.a[0].length) // 1000001

On v6.15.3, the first input parses successfully and the second creates an array with 1,000,001 elements. The equivalent a=1,2,3,4 input throws RangeError as expected.

Impact

An attacker who can supply a query string or form body can bypass configured array limits and force excessive memory allocation, causing denial of service. The limit must be applied after comma splitting and before the resulting array is wrapped.

Affected software

Click a technology to see all vulnerabilities affecting it.

Platform	Package	Vulnerable versions	Fixed in
npm package	qs	>= 6.14.2, < 6.16.0	6.16.0

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-770
Platform: npm
Package: qs
Disclosed: 02.09.2026
Updated: 11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-x5fp-wj9c-mxmx - 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

02.09.2026

qs array-limit bypass via bracket-key comma parsing this entry

Medium · 3.7 CVE-2026-82562 >= 6.14.2, < 6.16.0 6.16.0
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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