qs : qs.stringify with arrayFormat 'comma' throws an uncaught TypeError on array elements carrying a non-callable own toString (DoS)

{
  "id": "8bc2e302f9cf90d6927a19203aa41cee24cc3f94d8b2d1152110af68c30848de",
  "url": "https://osv.dev/vulnerability/GHSA-6pq8-jhm2-2vcw",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "qs : qs.stringify with arrayFormat 'comma' throws an uncaught TypeError on array elements carrying a non-callable own toString (DoS)",
    "summary": "## Summary `qs.stringify(obj, { arrayFormat: 'comma' })` throws an uncaught `TypeError: Cannot convert object to primitive value` when an array in `obj` contains an element that carries an own, non-callable `toString` property (for example `{ a: [ { toString: 'x' } ] }`). A remote, unauthenticated attacker who can influence an object that the application later re-serializes with the comma array format triggers the throw. In a service that lacks a synchronous error boundary around the serialization call, the uncaught exception crashes the worker process, producing a denial of service. ## Root Cause When `arrayFormat: 'comma'` is selected, the comma branch collapses the whole array into a single value via `Array.prototype.join`, or, under `encodeValuesOnly: true`, maps each element through the value encoder before joining. Both paths perform an implicit string coercion (`ToPrimitive` with hint `\"string\"`) on each element. For an object whose own `toString` is a non-callable value, coercion skips the shadowed non-callable `toString`, falls through to `Object.prototype.valueOf` (which returns the object rather than a primitive), and throws. The comma branch runs this coercion before the per-element null and skip handling in the main loop, so nothing downstream can neutralize the hostile element, and the throw is never caught inside the library. ```text lib/stringify.js (comma-array branch) line 152-154: obj = utils.maybeMap(obj, function (v) { return v == null ? v : encoder(v); }",
    "evidence": "osv:GHSA-6pq8-jhm2-2vcw",
    "products": [
      {
        "name": {
          "value": "qs",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.16.1",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "medium",
    "structured": {
      "id": "GHSA-6pq8-jhm2-2vcw",
      "aliases": [
        "CVE-2026-110816",
        "GHSA-6pq8-jhm2-2vcw"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
        },
        {
          "type": "CVSS_V4",
          "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:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.16.1"
                }
              ]
            }
          ],
          "package": {
            "name": "qs",
            "purl": "pkg:npm/qs",
            "ecosystem": "npm"
          },
          "database_specific": {
            "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-6pq8-jhm2-2vcw/GHSA-6pq8-jhm2-2vcw.json",
            "last_known_affected_version_range": "<= 6.16.0"
          }
        }
      ],
      "modified": "2026-10-27T16:15:05.324423680Z",
      "provider": "osv",
      "references": [
        "https://github.com/ljharb/qs/security/advisories/GHSA-6pq8-jhm2-2vcw",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-110816",
        "https://github.com/ljharb/qs/commit/a952e7519338ef0cfb25694a2988848f93333727",
        "https://github.com/ljharb/qs",
        "https://github.com/ljharb/qs/releases/tag/v6.16.1"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-248",
          "CWE-704"
        ],
        "severity": "MODERATE",
        "github_reviewed": true,
        "nvd_published_at": "2026-10-14T22:17:23Z",
        "github_reviewed_at": "2026-10-27T16:10:55Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-110816",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/1/score"
  },
  "source_id": "core-osv",
  "document_id": 462858,
  "published_at": "2026-10-27T16:10:55+00:00"
}