{"id":"DEBIAN-CVE-2026-2391","details":"### 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(',') \u003e -1) {     return val.split(','); }  if (options.throwOnLimitExceeded && currentArrayLength \u003e= 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.","modified":"2026-09-14T17:01:02.292958567Z","published":"2026-02-12T05:17:11.187Z","upstream":["CVE-2026-2391"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-2391"}],"affected":[{"package":{"name":"node-qs","ecosystem":"Debian:12","purl":"pkg:deb/debian/node-qs?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.11.0+ds+~6.9.7-3","6.11.0+ds+~6.9.7-4","6.13.0+ds+~6.9.16-1","6.14.1+ds+~6.14.0-1","6.15.0+ds+~6.15.0-1","6.15.0+ds+~6.15.0-2","6.15.0+ds+~6.15.0-3","6.15.2+ds+~6.15.1-1","6.16.0+ds+~6.15.1-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-2391.json"}},{"package":{"name":"node-qs","ecosystem":"Debian:13","purl":"pkg:deb/debian/node-qs?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.13.0+ds+~6.9.16-1","6.14.1+ds+~6.14.0-1","6.15.0+ds+~6.15.0-1","6.15.0+ds+~6.15.0-2","6.15.0+ds+~6.15.0-3","6.15.2+ds+~6.15.1-1","6.16.0+ds+~6.15.1-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-2391.json"}},{"package":{"name":"node-qs","ecosystem":"Debian:14","purl":"pkg:deb/debian/node-qs?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.15.0+ds+~6.15.0-1"}]}],"versions":["6.13.0+ds+~6.9.16-1","6.14.1+ds+~6.14.0-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-2391.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"}]}