GHSA-6RW7-VPXM-498P

Vulnerability from github – Published: 2025-12-30 21:02 – Updated: 2026-03-02 22:05
VLAI
Summary
qs's arrayLimit bypass in its bracket notation allows DoS via memory exhaustion
Details

Summary

The arrayLimit option in qs did not enforce limits for bracket notation (a[]=1&a[]=2), only for indexed notation (a[0]=1). This is a consistency bug; arrayLimit should apply uniformly across all array notations.

Note: The default parameterLimit of 1000 effectively mitigates the DoS scenario originally described. With default options, bracket notation cannot produce arrays larger than parameterLimit regardless of arrayLimit, because each a[]=value consumes one parameter slot. The severity has been reduced accordingly.

Details

The arrayLimit option only checked limits for indexed notation (a[0]=1&a[1]=2) but did not enforce it for bracket notation (a[]=1&a[]=2).

Vulnerable code (lib/parse.js:159-162):

if (root === '[]' && options.parseArrays) {
    obj = utils.combine([], leaf);  // No arrayLimit check
}

Working code (lib/parse.js:175):

else if (index <= options.arrayLimit) {  // Limit checked here
    obj = [];
    obj[index] = leaf;
}

The bracket notation handler at line 159 uses utils.combine([], leaf) without validating against options.arrayLimit, while indexed notation at line 175 checks index <= options.arrayLimit before creating arrays.

PoC

const qs = require('qs');
const result = qs.parse('a[]=1&a[]=2&a[]=3&a[]=4&a[]=5&a[]=6', { arrayLimit: 5 });
console.log(result.a.length);  // Output: 6 (should be max 5)

Note on parameterLimit interaction: The original advisory's "DoS demonstration" claimed a length of 10,000, but parameterLimit (default: 1000) caps parsing to 1,000 parameters. With default options, the actual output is 1,000, not 10,000.

Impact

Consistency bug in arrayLimit enforcement. With default parameterLimit, the practical DoS risk is negligible since parameterLimit already caps the total number of parsed parameters (and thus array elements from bracket notation). The risk increases only when parameterLimit is explicitly set to a very high value.

Severity
3.7 (Low)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
6.3 (Medium)
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:L
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "qs"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.14.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2025-15284"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2025-12-30T21:02:54Z",
    "nvd_published_at": "2025-12-29T23:15:42Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nThe `arrayLimit` option in qs did not enforce limits for bracket notation (`a[]=1\u0026a[]=2`), only for indexed notation (`a[0]=1`). This is a consistency bug; `arrayLimit` should apply uniformly across all array notations.\n\n**Note:** The default `parameterLimit` of 1000 effectively mitigates the DoS scenario originally described. With default options, bracket notation cannot produce arrays larger than `parameterLimit` regardless of `arrayLimit`, because each `a[]=value` consumes one parameter slot. The severity has been reduced accordingly.\n\n### Details\n\nThe `arrayLimit` option only checked limits for indexed notation (`a[0]=1\u0026a[1]=2`) but did not enforce it for bracket notation (`a[]=1\u0026a[]=2`).\n\n**Vulnerable code** (`lib/parse.js:159-162`):\n```javascript\nif (root === \u0027[]\u0027 \u0026\u0026 options.parseArrays) {\n    obj = utils.combine([], leaf);  // No arrayLimit check\n}\n```\n\n**Working code** (`lib/parse.js:175`):\n```javascript\nelse if (index \u003c= options.arrayLimit) {  // Limit checked here\n    obj = [];\n    obj[index] = leaf;\n}\n```\n\nThe bracket notation handler at line 159 uses `utils.combine([], leaf)` without validating against `options.arrayLimit`, while indexed notation at line 175 checks `index \u003c= options.arrayLimit` before creating arrays.\n\n### PoC\n\n```javascript\nconst qs = require(\u0027qs\u0027);\nconst result = qs.parse(\u0027a[]=1\u0026a[]=2\u0026a[]=3\u0026a[]=4\u0026a[]=5\u0026a[]=6\u0027, { arrayLimit: 5 });\nconsole.log(result.a.length);  // Output: 6 (should be max 5)\n```\n\n**Note on parameterLimit interaction:** The original advisory\u0027s \"DoS demonstration\" claimed a length of 10,000, but `parameterLimit` (default: 1000) caps parsing to 1,000 parameters. With default options, the actual output is 1,000, not 10,000.\n\n### Impact\n\nConsistency bug in `arrayLimit` enforcement. With default `parameterLimit`, the practical DoS risk is negligible since `parameterLimit` already caps the total number of parsed parameters (and thus array elements from bracket notation). The risk increases only when `parameterLimit` is explicitly set to a very high value.",
  "id": "GHSA-6rw7-vpxm-498p",
  "modified": "2026-03-02T22:05:33Z",
  "published": "2025-12-30T21:02:54Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/ljharb/qs/security/advisories/GHSA-6rw7-vpxm-498p"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-15284"
    },
    {
      "type": "WEB",
      "url": "https://github.com/ljharb/qs/commit/3086902ecf7f088d0d1803887643ac6c03d415b9"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/ljharb/qs"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:L",
      "type": "CVSS_V4"
    }
  ],
  "summary": "qs\u0027s arrayLimit bypass in its bracket notation allows DoS via memory exhaustion"
}



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