### Summary
The `arrayLimit` option in qs does not enforce limits for comma-separated values when `comma: true` is enabled, allowing attackers to cause denial-of-service via memory exhaustion. This is a bypass of the array limit enforcement, similar to the bracket notation bypass addressed in GHSA-6rw7-vpxm-498p (CVE-2025-15284).
### Details
When the `comma` option is set to `true` (not the default, but configurable in applications), qs allows parsing comma-separated strings as arrays (e.g., `?param=a,b,c` becomes `['a', 'b', 'c']`). However, the limit check for `arrayLimit` (default: 20) and the optional throwOnLimitExceeded occur after the comma-handling logic in `parseArrayValue`, enabling a bypass. This permits creation of arbitrarily large arrays from a single parameter, leading to excessive memory allocation.
**Vulnerable code** (lib/parse.js: lines ~40-50):
```js
if (val && typeof val === 'string' && options.comma && val.indexOf(',') > -1) {
return val.split(',');
}
if (options.throwOnLimitExceeded && currentArrayLength >= options.arrayLimit) {
throw new RangeError('Array limit exceeded. Only ' + options.arrayLimit + ' element' + (options.arrayLimit === 1 ? '' : 's') + ' allowed in an array.');
}
return val;
```
The `split(',')` returns the array immediately, skipping the subsequent limit check. Downstream merging via `utils.combine` does not prevent allocation, even if it marks overflows for sparse arrays.This discrepancy allows attackers to send a single parameter with millions of commas (e.g., `?param=,,,,,,,,...`), allocating massive arrays in memory without triggering limits. It bypasses the intent of `arrayLimit`, which is enforced correctly for indexed (`a[0]=`) and bracket (`a[]=`) notations (the latter fixed in v6.14.1 per GHSA-6rw7-vpxm-498p).
### PoC
**Test 1 - Basic bypass:**
```
npm install qs
```
```js
const qs = require('qs');
const payload = 'a=' + ','.repeat(25); // 26 elements after split (bypasses arrayLimit: 5)
const options = { comma: true, arrayLimit: 5, throwOnLimitExceeded: true };
try {
const result = qs.parse(payload, options);
console.log(result.a.length); // Outputs: 26 (bypass successful)
} catch (e) {
console.log('Limit enforced:', e.message); // Not thrown
}
```
**Configuration:**
- `comma: true`
- `arrayLimit: 5`
- `throwOnLimitExceeded: true`
Expected: Throws "Array limit exceeded" error.
Actual: Parses successfully, creating an array of length 26.
### Impact
Denial of Service (DoS) via memory exhaustion.
References
| Link | Resource |
|---|---|
| https://github.com/ljharb/qs/commit/f6a7abff1f13d644db9b05fe4f2c98ada6bf8482 | Patch |
| https://github.com/ljharb/qs/security/advisories/GHSA-w7fw-mjwx-w883 | Exploit Vendor Advisory |
| https://github.com/ljharb/qs/security/advisories/GHSA-w7fw-mjwx-w883 | Exploit Vendor Advisory |
Configurations
History
24 Feb 2026, 20:13
| Type | Values Removed | Values Added |
|---|---|---|
| References | () https://github.com/ljharb/qs/commit/f6a7abff1f13d644db9b05fe4f2c98ada6bf8482 - Patch | |
| References | () https://github.com/ljharb/qs/security/advisories/GHSA-w7fw-mjwx-w883 - Exploit, Vendor Advisory | |
| Summary |
|
|
| CWE | NVD-CWE-noinfo | |
| First Time |
Qs Project qs
Qs Project |
|
| CPE | cpe:2.3:a:qs_project:qs:*:*:*:*:*:node.js:*:* |
12 Feb 2026, 16:16
| Type | Values Removed | Values Added |
|---|---|---|
| References | () https://github.com/ljharb/qs/security/advisories/GHSA-w7fw-mjwx-w883 - |
12 Feb 2026, 05:17
| Type | Values Removed | Values Added |
|---|---|---|
| New CVE |
Information
Published : 2026-02-12 05:17
Updated : 2026-02-24 20:13
NVD link : CVE-2026-2391
Mitre link : CVE-2026-2391
CVE.ORG link : CVE-2026-2391
JSON object : View
Products Affected
qs_project
- qs
CWE