{"id":"CVE-2026-110816","title":"### Summary\n\n\n\n`qs.stringify` with `arrayFormat: 'comma'` throws `TypeError: Cannot convert object to primitive value` when an array element cannot be coerced to a string, such as an object with an own non-callable `toString` (`{ \"toStri…","summary":"### Summary\n\n\n\n`qs.stringify` with `arrayFormat: 'comma'` throws `TypeError: Cannot convert object to primitive value` when an array element cannot be coerced to a string, such as an object with an own non-callable `toString` (`{ \"toStri…","severity":"medium","cvss":5.3,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","cwe":["CWE-248","CWE-704"],"vendor":"ljharb","product":"qs","affected":["qs >= 6.7.0 < 6.16.1"],"patched":["hardened_images"],"published":"2026-10-14","updated":"2026-10-16","sourceUpdated":"2026-10-16T21:17:23.953","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-110816","references":[{"url":"https://github.com/ljharb/qs/commit/a952e7519338ef0cfb25694a2988848f93333727","label":"7ffcee3d-2c14-4c3e-b844-86c6a321a158"},{"url":"https://github.com/ljharb/qs/security/advisories/GHSA-6pq8-jhm2-2vcw","label":"7ffcee3d-2c14-4c3e-b844-86c6a321a158"},{"url":"https://github.com/ljharb/qs/security/advisories/GHSA-6pq8-jhm2-2vcw","label":"134c704f-9b21-4f2e-91b3-4a467353bcc0"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-110816.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-110816"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2552954"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-110816"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-110816"},{"url":"https://access.redhat.com/errata/RHSA-2026:85266"},{"url":"https://github.com/ljharb/qs/releases/tag/v6.16.1"},{"url":"https://github.com/advisories/GHSA-6pq8-jhm2-2vcw"}],"tags":["nvd","cve.org","exploit-available","csaf","vex","red-hat","ghsa","npm"],"epss":0.00368,"epssPercentile":0.30524,"aliases":["GHSA-6pq8-jhm2-2vcw"],"ecosystem":"npm","exploitAvailable":true,"ssvc":{"exploitation":"poc","automatable":"yes","technicalImpact":"partial","timestamp":"2026-10-16T20:17:24.605809Z"},"ingestedAt":"2026-10-14T23:00:02.042Z","slug":"CVE-2026-110816","body":"## Overview\n\n### Summary\n\n\n\n`qs.stringify` with `arrayFormat: 'comma'` throws `TypeError: Cannot convert object to primitive value` when an array element cannot be coerced to a string, such as an object with an own non-callable `toString` (`{ \"toString\": \"x\" }`) or a null-prototype object. The comma format joins array elements with `Array.prototype.join` and, under `encodeValuesOnly`, first passes each element through `String()` in `utils.encode`; neither guards against an element whose string coercion fails.\n\n\n\n### Details\n\n\n\nIn `lib/stringify.js`, the comma branch collapses the array with `obj.join(',')`. For an element whose own `toString` is not callable, `ToPrimitive` skips it, falls through to `Object.prototype.valueOf` (which returns the object itself), and throws. Under `encodeValuesOnly: true`, the same element first reaches `String(str)` in `utils.encode` (`lib/utils.js`) and throws there. Nested arrays (`{ \"a\": [[{ \"toString\": \"x\" }]] }`) throw the same way, through `Array.prototype.toString`. The `indices`, `brackets`, and `repeat` formats walk into object elements instead of coercing them, and are not affected.\n\n\n\nSuch elements can come from untrusted input. `JSON.parse` produces `{ \"a\": [{ \"toString\": \"x\" }] }` with no qs option involved. `qs.parse(\"a[0][toString]=x\", { allowPrototypes: true })` keeps the `toString` key, and `qs.parse(\"a[][b]=c\", { plainObjects: true })` produces a null-prototype element; the default parse options drop `toString` and produce ordinary objects, which do not throw. Express 4's default `query parser`, Express 5's `extended` query parser, and body-parser's `urlencoded({ extended: true })` all call `qs.parse` with `allowPrototypes: true`.\n\n\n\n#### PoC\n\n\n\n```js\n\n\n\nvar qs = require(\"qs\");\n\n\n\nqs.stringify(JSON.parse(\"{\\\"a\\\":[{\\\"toString\\\":\\\"x\\\"}]}\"), { arrayFormat: \"comma\" });\n\n\n\nqs.stringify(qs.parse(\"a[0][toString]=x\", { allowPrototypes: true }), { arrayFormat: \"comma\" });\n\n\n\nqs.stringify(qs.parse(\"a[][b]=c\", { plainObjects: true }), { arrayFormat: \"comma\", encodeValuesOnly: true });\n\n\n\n// TypeError: Cannot convert object to primitive value\n\n\n\n```\n\n\n\n#### Fix\n\n\n\nApplied in a952e75 on `main` and released as v6.16.1: an element whose string coercion would fail is coerced to its primitive `valueOf`, if any, or else to `Object.prototype.toString`, so it renders as `[object Object]`, the same as any other object element already does under the comma format. Nested arrays are walked the way `join` walks them. Every input that did not previously throw serializes exactly as before, and a `toString` or `valueOf` that itself throws still propagates.\n\n\n\n### Affected versions\n\n\n\n`>=6.7.0 <6.16.1`, fixed in v6.16.1.\n\n\n\nThe `join` path was introduced with the comma format in b84acba and first shipped in v6.7.0; v6.6.x and earlier ignore `arrayFormat: 'comma'` and are not affected. The `encodeValuesOnly` `String()` site was introduced in 4c4b23d (v6.11.1); before that, the same input throws at `join`. Every release from v6.7.0 through v6.16.0 is affected.\n\n\n\n### Impact\n\n\n\nAn unauthenticated request can make any code path that re-serializes attacker-influenced data with `qs.stringify` and `arrayFormat: 'comma'` (for example, rebuilding a query string from `req.query` for a redirect or an upstream request, or serializing a parsed JSON body) throw synchronously. In a typical Node.js HTTP framework the throw is caught by the framework error boundary and the affected request returns a 500; the process survives and other requests are unaffected. Where the call runs outside an error boundary, such as an `async` Express 4 handler (where the throw becomes an unhandled promise rejection) or a bare `http` request handler, the process exits, so the impact in that case depends on the application error handling rather than on qs. The default `arrayFormat` (`indices`) is not affected.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Package advisory (CVE-2026-110816)\n\nAffected packages:\n\n- `qs >= 6.7.0, <= 6.16.0`\n\nPatched in:\n\n- `qs 6.16.1`\n\nSource: https://github.com/advisories/GHSA-6pq8-jhm2-2vcw\n\n## Vendor advisories\n\n- **RHSA-2026:85266** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-10-19 · [advisory](https://access.redhat.com/errata/RHSA-2026:85266)\n- **Red Hat VEX** · Moderate · affected: Red Hat Hardened Images · no fix planned: Red Hat Hardened Images · updated 2026-10-20 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-110816.json)","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":29.2,"likelihood":0.1,"exploitation":12,"ransomware":0},"changes":[{"seq":223375,"id":"CVE-2026-110816","ts":1792183952826,"field":"exploit_available","old":"false","new":"true"}]}