CVE-2026-110816 (GCVE-0-2026-110816)
Vulnerability from cvelistv5
Published
2026-10-14 22:05
Modified
2026-10-16 20:17
Severity ?
5.3 (Medium) - CVSS:3.1/AV:N/AC:L/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:N
CWE
  • CWE-248 - Uncaught Exception
  • CWE-704 - Incorrect Type Conversion or Cast
Summary
### Summary `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. ### Details 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. 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`. #### PoC ```js var qs = require("qs"); qs.stringify(JSON.parse("{\"a\":[{\"toString\":\"x\"}]}"), { arrayFormat: "comma" }); qs.stringify(qs.parse("a[0][toString]=x", { allowPrototypes: true }), { arrayFormat: "comma" }); qs.stringify(qs.parse("a[][b]=c", { plainObjects: true }), { arrayFormat: "comma", encodeValuesOnly: true }); // TypeError: Cannot convert object to primitive value ``` #### Fix 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. ### Affected versions `>=6.7.0 <6.16.1`, fixed in v6.16.1. 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. ### Impact 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.
References
Impacted products
Vendor Product Version
ljharb qs Version: 6.7.0   ≤
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              "value": "\u003cp\u003e### Summary\u003c/p\u003e\u003cp\u003e`qs.stringify` with `arrayFormat: \u0027comma\u0027` 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.\u003c/p\u003e\u003cp\u003e### Details\u003c/p\u003e\u003cp\u003eIn `lib/stringify.js`, the comma branch collapses the array with `obj.join(\u0027,\u0027)`. 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.\u003c/p\u003e\u003cp\u003eSuch 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\u0027s default `query parser`, Express 5\u0027s `extended` query parser, and body-parser\u0027s `urlencoded({ extended: true })` all call `qs.parse` with `allowPrototypes: true`.\u003c/p\u003e\u003cp\u003e#### PoC\u003c/p\u003e\u003cp\u003e```js\u003c/p\u003e\u003cp\u003evar qs = require(\"qs\");\u003c/p\u003e\u003cp\u003eqs.stringify(JSON.parse(\"{\\\"a\\\":[{\\\"toString\\\":\\\"x\\\"}]}\"), { arrayFormat: \"comma\" });\u003c/p\u003e\u003cp\u003eqs.stringify(qs.parse(\"a[0][toString]=x\", { allowPrototypes: true }), { arrayFormat: \"comma\" });\u003c/p\u003e\u003cp\u003eqs.stringify(qs.parse(\"a[][b]=c\", { plainObjects: true }), { arrayFormat: \"comma\", encodeValuesOnly: true });\u003c/p\u003e\u003cp\u003e// TypeError: Cannot convert object to primitive value\u003c/p\u003e\u003cp\u003e```\u003c/p\u003e\u003cp\u003e#### Fix\u003c/p\u003e\u003cp\u003eApplied 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.\u003c/p\u003e\u003cp\u003e### Affected versions\u003c/p\u003e\u003cp\u003e`\u0026gt;=6.7.0 \u0026lt;6.16.1`, fixed in v6.16.1.\u003c/p\u003e\u003cp\u003eThe `join` path was introduced with the comma format in b84acba and first shipped in v6.7.0; v6.6.x and earlier ignore `arrayFormat: \u0027comma\u0027` 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.\u003c/p\u003e\u003cp\u003e### Impact\u003c/p\u003e\u003cp\u003eAn unauthenticated request can make any code path that re-serializes attacker-influenced data with `qs.stringify` and `arrayFormat: \u0027comma\u0027` (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.\u003c/p\u003e"
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              "value": "\u003cp\u003eUse 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`.\u003c/p\u003e"
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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`.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eUse 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`.\u003c/p\u003e\", \"base64\": false}]}], \"descriptions\": [{\"lang\": \"en\", \"value\": \"### Summary\\n\\n\\n\\n`qs.stringify` with `arrayFormat: \u0027comma\u0027` 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(\u0027,\u0027)`. 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\u0027s default `query parser`, Express 5\u0027s `extended` query parser, and body-parser\u0027s `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`\u003e=6.7.0 \u003c6.16.1`, 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: \u0027comma\u0027` 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: \u0027comma\u0027` (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.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003e### Summary\u003c/p\u003e\u003cp\u003e`qs.stringify` with `arrayFormat: \u0027comma\u0027` 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.\u003c/p\u003e\u003cp\u003e### Details\u003c/p\u003e\u003cp\u003eIn `lib/stringify.js`, the comma branch collapses the array with `obj.join(\u0027,\u0027)`. 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.\u003c/p\u003e\u003cp\u003eSuch 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\u0027s default `query parser`, Express 5\u0027s `extended` query parser, and body-parser\u0027s `urlencoded({ extended: true })` all call `qs.parse` with `allowPrototypes: true`.\u003c/p\u003e\u003cp\u003e#### PoC\u003c/p\u003e\u003cp\u003e```js\u003c/p\u003e\u003cp\u003evar qs = require(\\\"qs\\\");\u003c/p\u003e\u003cp\u003eqs.stringify(JSON.parse(\\\"{\\\\\\\"a\\\\\\\":[{\\\\\\\"toString\\\\\\\":\\\\\\\"x\\\\\\\"}]}\\\"), { arrayFormat: \\\"comma\\\" });\u003c/p\u003e\u003cp\u003eqs.stringify(qs.parse(\\\"a[0][toString]=x\\\", { allowPrototypes: true }), { arrayFormat: \\\"comma\\\" });\u003c/p\u003e\u003cp\u003eqs.stringify(qs.parse(\\\"a[][b]=c\\\", { plainObjects: true }), { arrayFormat: \\\"comma\\\", encodeValuesOnly: true });\u003c/p\u003e\u003cp\u003e// TypeError: Cannot convert object to primitive value\u003c/p\u003e\u003cp\u003e```\u003c/p\u003e\u003cp\u003e#### Fix\u003c/p\u003e\u003cp\u003eApplied 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.\u003c/p\u003e\u003cp\u003e### Affected versions\u003c/p\u003e\u003cp\u003e`\u0026gt;=6.7.0 \u0026lt;6.16.1`, fixed in v6.16.1.\u003c/p\u003e\u003cp\u003eThe `join` path was introduced with the comma format in b84acba and first shipped in v6.7.0; v6.6.x and earlier ignore `arrayFormat: \u0027comma\u0027` 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.\u003c/p\u003e\u003cp\u003e### Impact\u003c/p\u003e\u003cp\u003eAn unauthenticated request can make any code path that re-serializes attacker-influenced data with `qs.stringify` and `arrayFormat: \u0027comma\u0027` (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.\u003c/p\u003e\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-248\", \"description\": \"CWE-248 Uncaught Exception\"}]}, {\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-704\", \"description\": \"CWE-704 Incorrect Type Conversion or Cast\"}]}], \"providerMetadata\": {\"orgId\": \"7ffcee3d-2c14-4c3e-b844-86c6a321a158\", \"shortName\": \"harborist\", \"dateUpdated\": \"2026-10-14T22:05:24.015Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-110816\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-10-16T20:17:48.588Z\", \"dateReserved\": \"2026-10-14T21:40:55.805Z\", \"assignerOrgId\": \"7ffcee3d-2c14-4c3e-b844-86c6a321a158\", \"datePublished\": \"2026-10-14T22:05:24.015Z\", \"assignerShortName\": \"harborist\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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