CVE-2026-2391

Date: February 11, 2026

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): 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 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.