{"id":"CVE-2026-2391","details":"### Summary\nThe `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).\n\n### Details\nWhen 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.\n\n**Vulnerable code** (lib/parse.js: lines ~40-50):\n```js\nif (val && typeof val === 'string' && options.comma && val.indexOf(',') \u003e -1) {\n    return val.split(',');\n}\n\nif (options.throwOnLimitExceeded && currentArrayLength \u003e= options.arrayLimit) {\n    throw new RangeError('Array limit exceeded. Only ' + options.arrayLimit + ' element' + (options.arrayLimit === 1 ? '' : 's') + ' allowed in an array.');\n}\n\nreturn val;\n```\nThe `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).\n\n### PoC\n**Test 1 - Basic bypass:**\n```\nnpm install qs\n```\n\n```js\nconst qs = require('qs');\n\nconst payload = 'a=' + ','.repeat(25);  // 26 elements after split (bypasses arrayLimit: 5)\nconst options = { comma: true, arrayLimit: 5, throwOnLimitExceeded: true };\n\ntry {\n  const result = qs.parse(payload, options);\n  console.log(result.a.length);  // Outputs: 26 (bypass successful)\n} catch (e) {\n  console.log('Limit enforced:', e.message);  // Not thrown\n}\n```\n**Configuration:**\n- `comma: true`\n- `arrayLimit: 5`\n- `throwOnLimitExceeded: true`\n\nExpected: Throws \"Array limit exceeded\" error.\nActual: Parses successfully, creating an array of length 26.\n\n\n### Impact\nDenial of Service (DoS) via memory exhaustion.","aliases":["GHSA-w7fw-mjwx-w883"],"modified":"2026-04-10T05:39:17.102223Z","published":"2026-02-12T05:17:11.187Z","related":["CGA-3mq6-2fwj-jgmr","GHSA-w7fw-mjwx-w883"],"references":[{"type":"FIX","url":"https://github.com/ljharb/qs/commit/f6a7abff1f13d644db9b05fe4f2c98ada6bf8482"},{"type":"EVIDENCE","url":"https://github.com/ljharb/qs/security/advisories/GHSA-w7fw-mjwx-w883"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/ljharb/qs","events":[{"introduced":"125e103b61f2bef245970f5a2a8dceffe5aab59a"},{"fixed":"bdcf0c7f82387c18ac8fabfccd2f440645cef47b"},{"fixed":"f6a7abff1f13d644db9b05fe4f2c98ada6bf8482"}],"database_specific":{"versions":[{"introduced":"6.7.0"},{"fixed":"6.14.2"}]}}],"versions":["v6.10.0","v6.10.1","v6.10.2","v6.10.3","v6.10.4","v6.10.5","v6.11.0","v6.11.1","v6.11.2","v6.12.0","v6.12.1","v6.12.2","v6.12.3","v6.13.0","v6.13.1","v6.14.0","v6.14.1","v6.7.0","v6.8.0","v6.9.0","v6.9.1","v6.9.2","v6.9.3","v6.9.4","v6.9.5","v6.9.6"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-2391.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"}]}