{
    "dataType": "CVE_RECORD",
    "dataVersion": "5.2",
    "cveMetadata": {
        "cveId": "CVE-2026-110816",
        "assignerOrgId": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
        "state": "PUBLISHED",
        "assignerShortName": "harborist",
        "dateReserved": "2026-10-14T21:40:55.805Z",
        "datePublished": "2026-10-14T22:05:24.015Z",
        "dateUpdated": "2026-10-16T20:17:48.588Z"
    },
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                "orgId": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
                "shortName": "harborist",
                "dateUpdated": "2026-10-14T22:05:24.015Z"
            },
            "title": "qs.stringify with arrayFormat comma throws TypeError on array elements that cannot be coerced to a string",
            "problemTypes": [
                {
                    "descriptions": [
                        {
                            "lang": "en",
                            "cweId": "CWE-248",
                            "description": "CWE-248 Uncaught Exception",
                            "type": "CWE"
                        }
                    ]
                },
                {
                    "descriptions": [
                        {
                            "lang": "en",
                            "cweId": "CWE-704",
                            "description": "CWE-704 Incorrect Type Conversion or Cast",
                            "type": "CWE"
                        }
                    ]
                }
            ],
            "affected": [
                {
                    "vendor": "ljharb",
                    "product": "qs",
                    "collectionURL": "https://npmjs.com/qs",
                    "packageName": "qs",
                    "repo": "https://github.com/ljharb/qs",
                    "versions": [
                        {
                            "status": "affected",
                            "version": "6.7.0",
                            "lessThan": "6.16.1",
                            "versionType": "semver"
                        }
                    ],
                    "defaultStatus": "unaffected"
                }
            ],
            "descriptions": [
                {
                    "lang": "en",
                    "value": "### 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.",
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                            "value": "<p>### Summary</p><p>`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.</p><p>### Details</p><p>In `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.</p><p>Such 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`.</p><p>#### PoC</p><p>```js</p><p>var qs = require(\"qs\");</p><p>qs.stringify(JSON.parse(\"{\\\"a\\\":[{\\\"toString\\\":\\\"x\\\"}]}\"), { arrayFormat: \"comma\" });</p><p>qs.stringify(qs.parse(\"a[0][toString]=x\", { allowPrototypes: true }), { arrayFormat: \"comma\" });</p><p>qs.stringify(qs.parse(\"a[][b]=c\", { plainObjects: true }), { arrayFormat: \"comma\", encodeValuesOnly: true });</p><p>// TypeError: Cannot convert object to primitive value</p><p>```</p><p>#### Fix</p><p>Applied 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.</p><p>### Affected versions</p><p>`&gt;=6.7.0 &lt;6.16.1`, fixed in v6.16.1.</p><p>The `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.</p><p>### Impact</p><p>An 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.</p>"
                        }
                    ]
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            "references": [
                {
                    "url": "https://github.com/ljharb/qs/security/advisories/GHSA-6pq8-jhm2-2vcw",
                    "tags": [
                        "vendor-advisory"
                    ]
                },
                {
                    "url": "https://github.com/ljharb/qs/commit/a952e7519338ef0cfb25694a2988848f93333727",
                    "tags": [
                        "patch"
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                        "privilegesRequired": "NONE",
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                        "subIntegrityImpact": "NONE",
                        "vulnAvailabilityImpact": "LOW",
                        "subAvailabilityImpact": "NONE",
                        "exploitMaturity": "NOT_DEFINED",
                        "Safety": "NOT_DEFINED",
                        "Automatable": "NOT_DEFINED",
                        "Recovery": "NOT_DEFINED",
                        "valueDensity": "NOT_DEFINED",
                        "vulnerabilityResponseEffort": "NOT_DEFINED",
                        "providerUrgency": "NOT_DEFINED",
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            "workarounds": [
                {
                    "lang": "en",
                    "value": "Use the default `arrayFormat` (`indices`), or pass a `filter` function to `qs.stringify` that replaces non-primitive array elements before the comma format joins them. Alternatively, wrap `qs.stringify` calls on externally influenced objects in try/catch, and avoid `allowPrototypes: true` / `plainObjects: true` when parsed untrusted input is fed back into `qs.stringify`.",
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            "solutions": [
                {
                    "lang": "en",
                    "value": "Upgrade to qs 6.16.1 or later.",
                    "supportingMedia": [
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                            "base64": false,
                            "value": "<p>Upgrade to qs 6.16.1 or later.</p>"
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                                "timestamp": "2026-10-16T20:17:24.605809Z",
                                "id": "CVE-2026-110816",
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                                "role": "CISA Coordinator",
                                "version": "2.0.3"
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                "title": "CISA ADP Vulnrichment",
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