CVE-2026-82417 (GCVE-0-2026-82417)
Vulnerability from cvelistv5
Published
2026-08-29 23:51
Modified
2026-08-31 17:08
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-703 - Improper Check or Handling of Exceptional Conditions
Summary
### Summary `qs.stringify` throws a `TypeError` when it serializes an object whose own `constructor` property has a truthy, non-callable `isBuffer` member. `utils.isBuffer` duck-types buffers by calling `obj.constructor.isBuffer(obj)` after checking only that the property is truthy, so a value such as `{ constructor: { isBuffer: "x" } }` makes the call throw `TypeError: obj.constructor.isBuffer is not a function`. ### Details `lib/stringify.js:127` calls `utils.isBuffer` on every non-primitive value it serializes. `utils.isBuffer` (`lib/utils.js:332`) reads `obj.constructor.isBuffer` and invokes it without verifying that it is a function. `constructor` and `isBuffer` are ordinary property names, so any object carrying them as own properties reaches the unchecked call. Such an object can be built from untrusted input. `qs.parse("x[constructor][isBuffer]=y", { plainObjects: true })` or `{ allowPrototypes: true }` keeps the `constructor` key as an own property (the default parse options drop it), and `JSON.parse("{\"a\":{\"constructor\":{\"isBuffer\":\"x\"}}}")` produces the same shape with no qs option involved. Express 4 with its default `query parser` setting and body-parser with `extended: true` both call `qs.parse` with `allowPrototypes: true`, so on those stacks `req.query` and `req.body` can carry the shape directly. #### PoC ```js var qs = require("qs"); qs.stringify(qs.parse("x[constructor][isBuffer]=y", { plainObjects: true })); qs.stringify(JSON.parse("{\"a\":{\"constructor\":{\"isBuffer\":\"x\"}}}")); // TypeError: obj.constructor.isBuffer is not a function // at Object.isBuffer (lib/utils.js:332:78) // at stringify (lib/stringify.js:127:45) ``` #### Fix `lib/utils.js`, applied in e83d321 on `main` and released as v6.16.0: ```diff - return !!(obj.constructor && obj.constructor.isBuffer && obj.constructor.isBuffer(obj)); + return !!(obj.constructor && typeof obj.constructor.isBuffer === "function" && obj.constructor.isBuffer(obj)); ``` Real `Buffer`, `safer-buffer`, and browserify `buffer` polyfill instances serialize exactly as before; only the throw is removed. ### Affected versions `>=2.2.5 <6.16.0`, fixed in v6.16.0. The unguarded duck-type was introduced in 3768a75 and first shipped in v2.2.5 (September 2014). v2.2.4 and earlier used `Buffer.isBuffer` and are not affected. Every release from v2.2.5 through v6.15.3 contains the unguarded call. ### Impact An unauthenticated request can make any code path that re-serializes attacker-influenced data with `qs.stringify` (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 background job, the process exits, so the impact in that case depends on the application error handling rather than on qs.
References
Impacted products
Vendor Product Version
ljharb qs Version: 2.2.5   ≤
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              "value": "\u003cp\u003e### Summary\u003c/p\u003e\u003cp\u003e`qs.stringify` throws a `TypeError` when it serializes an object whose own `constructor` property has a truthy, non-callable `isBuffer` member. `utils.isBuffer` duck-types buffers by calling `obj.constructor.isBuffer(obj)` after checking only that the property is truthy, so a value such as `{ constructor: { isBuffer: \"x\" } }` makes the call throw `TypeError: obj.constructor.isBuffer is not a function`.\u003c/p\u003e\u003cp\u003e### Details\u003c/p\u003e\u003cp\u003e`lib/stringify.js:127` calls `utils.isBuffer` on every non-primitive value it serializes. `utils.isBuffer` (`lib/utils.js:332`) reads `obj.constructor.isBuffer` and invokes it without verifying that it is a function. `constructor` and `isBuffer` are ordinary property names, so any object carrying them as own properties reaches the unchecked call.\u003c/p\u003e\u003cp\u003eSuch an object can be built from untrusted input. `qs.parse(\"x[constructor][isBuffer]=y\", { plainObjects: true })` or `{ allowPrototypes: true }` keeps the `constructor` key as an own property (the default parse options drop it), and `JSON.parse(\"{\\\"a\\\":{\\\"constructor\\\":{\\\"isBuffer\\\":\\\"x\\\"}}}\")` produces the same shape with no qs option involved. Express 4 with its default `query parser` setting and body-parser with `extended: true` both call `qs.parse` with `allowPrototypes: true`, so on those stacks `req.query` and `req.body` can carry the shape directly.\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(qs.parse(\"x[constructor][isBuffer]=y\", { plainObjects: true }));\u003c/p\u003e\u003cp\u003eqs.stringify(JSON.parse(\"{\\\"a\\\":{\\\"constructor\\\":{\\\"isBuffer\\\":\\\"x\\\"}}}\"));\u003c/p\u003e\u003cp\u003e// TypeError: obj.constructor.isBuffer is not a function\u003c/p\u003e\u003cp\u003e//     at Object.isBuffer (lib/utils.js:332:78)\u003c/p\u003e\u003cp\u003e//     at stringify (lib/stringify.js:127:45)\u003c/p\u003e\u003cp\u003e```\u003c/p\u003e\u003cp\u003e#### Fix\u003c/p\u003e\u003cp\u003e`lib/utils.js`, applied in e83d321 on `main` and released as v6.16.0:\u003c/p\u003e\u003cp\u003e```diff\u003c/p\u003e\u003cp\u003e- return !!(obj.constructor \u0026amp;\u0026amp; obj.constructor.isBuffer \u0026amp;\u0026amp; obj.constructor.isBuffer(obj));\u003c/p\u003e\u003cp\u003e+ return !!(obj.constructor \u0026amp;\u0026amp; typeof obj.constructor.isBuffer === \"function\" \u0026amp;\u0026amp; obj.constructor.isBuffer(obj));\u003c/p\u003e\u003cp\u003e```\u003c/p\u003e\u003cp\u003eReal `Buffer`, `safer-buffer`, and browserify `buffer` polyfill instances serialize exactly as before; only the throw is removed.\u003c/p\u003e\u003cp\u003e### Affected versions\u003c/p\u003e\u003cp\u003e`\u0026gt;=2.2.5 \u0026lt;6.16.0`, fixed in v6.16.0.\u003c/p\u003e\u003cp\u003eThe unguarded duck-type was introduced in 3768a75 and first shipped in v2.2.5 (September 2014). v2.2.4 and earlier used `Buffer.isBuffer` and are not affected. Every release from v2.2.5 through v6.15.3 contains the unguarded call.\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` (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 background job, the process exits, so the impact in that case depends on the application error handling rather than on qs.\u003c/p\u003e"
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          "value": "### Summary\n\n\n\n`qs.stringify` throws a `TypeError` when it serializes an object whose own `constructor` property has a truthy, non-callable `isBuffer` member. `utils.isBuffer` duck-types buffers by calling `obj.constructor.isBuffer(obj)` after checking only that the property is truthy, so a value such as `{ constructor: { isBuffer: \"x\" } }` makes the call throw `TypeError: obj.constructor.isBuffer is not a function`.\n\n\n\n### Details\n\n\n\n`lib/stringify.js:127` calls `utils.isBuffer` on every non-primitive value it serializes. `utils.isBuffer` (`lib/utils.js:332`) reads `obj.constructor.isBuffer` and invokes it without verifying that it is a function. `constructor` and `isBuffer` are ordinary property names, so any object carrying them as own properties reaches the unchecked call.\n\n\n\nSuch an object can be built from untrusted input. `qs.parse(\"x[constructor][isBuffer]=y\", { plainObjects: true })` or `{ allowPrototypes: true }` keeps the `constructor` key as an own property (the default parse options drop it), and `JSON.parse(\"{\\\"a\\\":{\\\"constructor\\\":{\\\"isBuffer\\\":\\\"x\\\"}}}\")` produces the same shape with no qs option involved. Express 4 with its default `query parser` setting and body-parser with `extended: true` both call `qs.parse` with `allowPrototypes: true`, so on those stacks `req.query` and `req.body` can carry the shape directly.\n\n\n\n#### PoC\n\n\n\n```js\n\n\n\nvar qs = require(\"qs\");\n\n\n\nqs.stringify(qs.parse(\"x[constructor][isBuffer]=y\", { plainObjects: true }));\n\n\n\nqs.stringify(JSON.parse(\"{\\\"a\\\":{\\\"constructor\\\":{\\\"isBuffer\\\":\\\"x\\\"}}}\"));\n\n\n\n// TypeError: obj.constructor.isBuffer is not a function\n\n\n\n//     at Object.isBuffer (lib/utils.js:332:78)\n\n\n\n//     at stringify (lib/stringify.js:127:45)\n\n\n\n```\n\n\n\n#### Fix\n\n\n\n`lib/utils.js`, applied in e83d321 on `main` and released as v6.16.0:\n\n\n\n```diff\n\n\n\n- return !!(obj.constructor \u0026\u0026 obj.constructor.isBuffer \u0026\u0026 obj.constructor.isBuffer(obj));\n\n\n\n+ return !!(obj.constructor \u0026\u0026 typeof obj.constructor.isBuffer === \"function\" \u0026\u0026 obj.constructor.isBuffer(obj));\n\n\n\n```\n\n\n\nReal `Buffer`, `safer-buffer`, and browserify `buffer` polyfill instances serialize exactly as before; only the throw is removed.\n\n\n\n### Affected versions\n\n\n\n`\u003e=2.2.5 \u003c6.16.0`, fixed in v6.16.0.\n\n\n\nThe unguarded duck-type was introduced in 3768a75 and first shipped in v2.2.5 (September 2014). v2.2.4 and earlier used `Buffer.isBuffer` and are not affected. Every release from v2.2.5 through v6.15.3 contains the unguarded call.\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` (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 background job, the process exits, so the impact in that case depends on the application error handling rather than on qs."
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              "value": "\u003cp\u003ePass a `filter` function to `qs.stringify` that drops values carrying an own `constructor` property; it runs before the `isBuffer` check. 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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    "datePublished": "2026-08-29T23:51:27.634Z",
    "dateReserved": "2026-08-28T23:08:00.460Z",
    "dateUpdated": "2026-08-31T17:08:24.074Z",
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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\u003ePass a `filter` function to `qs.stringify` that drops values carrying an own `constructor` property; it runs before the `isBuffer` check. 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` throws a `TypeError` when it serializes an object whose own `constructor` property has a truthy, non-callable `isBuffer` member. `utils.isBuffer` duck-types buffers by calling `obj.constructor.isBuffer(obj)` after checking only that the property is truthy, so a value such as `{ constructor: { isBuffer: \\\"x\\\" } }` makes the call throw `TypeError: obj.constructor.isBuffer is not a function`.\\n\\n\\n\\n### Details\\n\\n\\n\\n`lib/stringify.js:127` calls `utils.isBuffer` on every non-primitive value it serializes. `utils.isBuffer` (`lib/utils.js:332`) reads `obj.constructor.isBuffer` and invokes it without verifying that it is a function. `constructor` and `isBuffer` are ordinary property names, so any object carrying them as own properties reaches the unchecked call.\\n\\n\\n\\nSuch an object can be built from untrusted input. `qs.parse(\\\"x[constructor][isBuffer]=y\\\", { plainObjects: true })` or `{ allowPrototypes: true }` keeps the `constructor` key as an own property (the default parse options drop it), and `JSON.parse(\\\"{\\\\\\\"a\\\\\\\":{\\\\\\\"constructor\\\\\\\":{\\\\\\\"isBuffer\\\\\\\":\\\\\\\"x\\\\\\\"}}}\\\")` produces the same shape with no qs option involved. Express 4 with its default `query parser` setting and body-parser with `extended: true` both call `qs.parse` with `allowPrototypes: true`, so on those stacks `req.query` and `req.body` can carry the shape directly.\\n\\n\\n\\n#### PoC\\n\\n\\n\\n```js\\n\\n\\n\\nvar qs = require(\\\"qs\\\");\\n\\n\\n\\nqs.stringify(qs.parse(\\\"x[constructor][isBuffer]=y\\\", { plainObjects: true }));\\n\\n\\n\\nqs.stringify(JSON.parse(\\\"{\\\\\\\"a\\\\\\\":{\\\\\\\"constructor\\\\\\\":{\\\\\\\"isBuffer\\\\\\\":\\\\\\\"x\\\\\\\"}}}\\\"));\\n\\n\\n\\n// TypeError: obj.constructor.isBuffer is not a function\\n\\n\\n\\n//     at Object.isBuffer (lib/utils.js:332:78)\\n\\n\\n\\n//     at stringify (lib/stringify.js:127:45)\\n\\n\\n\\n```\\n\\n\\n\\n#### Fix\\n\\n\\n\\n`lib/utils.js`, applied in e83d321 on `main` and released as v6.16.0:\\n\\n\\n\\n```diff\\n\\n\\n\\n- return !!(obj.constructor \u0026\u0026 obj.constructor.isBuffer \u0026\u0026 obj.constructor.isBuffer(obj));\\n\\n\\n\\n+ return !!(obj.constructor \u0026\u0026 typeof obj.constructor.isBuffer === \\\"function\\\" \u0026\u0026 obj.constructor.isBuffer(obj));\\n\\n\\n\\n```\\n\\n\\n\\nReal `Buffer`, `safer-buffer`, and browserify `buffer` polyfill instances serialize exactly as before; only the throw is removed.\\n\\n\\n\\n### Affected versions\\n\\n\\n\\n`\u003e=2.2.5 \u003c6.16.0`, fixed in v6.16.0.\\n\\n\\n\\nThe unguarded duck-type was introduced in 3768a75 and first shipped in v2.2.5 (September 2014). v2.2.4 and earlier used `Buffer.isBuffer` and are not affected. Every release from v2.2.5 through v6.15.3 contains the unguarded call.\\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` (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 background job, the process exits, so the impact in that case depends on the application error handling rather than on qs.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003e### Summary\u003c/p\u003e\u003cp\u003e`qs.stringify` throws a `TypeError` when it serializes an object whose own `constructor` property has a truthy, non-callable `isBuffer` member. `utils.isBuffer` duck-types buffers by calling `obj.constructor.isBuffer(obj)` after checking only that the property is truthy, so a value such as `{ constructor: { isBuffer: \\\"x\\\" } }` makes the call throw `TypeError: obj.constructor.isBuffer is not a function`.\u003c/p\u003e\u003cp\u003e### Details\u003c/p\u003e\u003cp\u003e`lib/stringify.js:127` calls `utils.isBuffer` on every non-primitive value it serializes. `utils.isBuffer` (`lib/utils.js:332`) reads `obj.constructor.isBuffer` and invokes it without verifying that it is a function. `constructor` and `isBuffer` are ordinary property names, so any object carrying them as own properties reaches the unchecked call.\u003c/p\u003e\u003cp\u003eSuch an object can be built from untrusted input. `qs.parse(\\\"x[constructor][isBuffer]=y\\\", { plainObjects: true })` or `{ allowPrototypes: true }` keeps the `constructor` key as an own property (the default parse options drop it), and `JSON.parse(\\\"{\\\\\\\"a\\\\\\\":{\\\\\\\"constructor\\\\\\\":{\\\\\\\"isBuffer\\\\\\\":\\\\\\\"x\\\\\\\"}}}\\\")` produces the same shape with no qs option involved. Express 4 with its default `query parser` setting and body-parser with `extended: true` both call `qs.parse` with `allowPrototypes: true`, so on those stacks `req.query` and `req.body` can carry the shape directly.\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(qs.parse(\\\"x[constructor][isBuffer]=y\\\", { plainObjects: true }));\u003c/p\u003e\u003cp\u003eqs.stringify(JSON.parse(\\\"{\\\\\\\"a\\\\\\\":{\\\\\\\"constructor\\\\\\\":{\\\\\\\"isBuffer\\\\\\\":\\\\\\\"x\\\\\\\"}}}\\\"));\u003c/p\u003e\u003cp\u003e// TypeError: obj.constructor.isBuffer is not a function\u003c/p\u003e\u003cp\u003e//     at Object.isBuffer (lib/utils.js:332:78)\u003c/p\u003e\u003cp\u003e//     at stringify (lib/stringify.js:127:45)\u003c/p\u003e\u003cp\u003e```\u003c/p\u003e\u003cp\u003e#### Fix\u003c/p\u003e\u003cp\u003e`lib/utils.js`, applied in e83d321 on `main` and released as v6.16.0:\u003c/p\u003e\u003cp\u003e```diff\u003c/p\u003e\u003cp\u003e- return !!(obj.constructor \u0026amp;\u0026amp; obj.constructor.isBuffer \u0026amp;\u0026amp; obj.constructor.isBuffer(obj));\u003c/p\u003e\u003cp\u003e+ return !!(obj.constructor \u0026amp;\u0026amp; typeof obj.constructor.isBuffer === \\\"function\\\" \u0026amp;\u0026amp; obj.constructor.isBuffer(obj));\u003c/p\u003e\u003cp\u003e```\u003c/p\u003e\u003cp\u003eReal `Buffer`, `safer-buffer`, and browserify `buffer` polyfill instances serialize exactly as before; only the throw is removed.\u003c/p\u003e\u003cp\u003e### Affected versions\u003c/p\u003e\u003cp\u003e`\u0026gt;=2.2.5 \u0026lt;6.16.0`, fixed in v6.16.0.\u003c/p\u003e\u003cp\u003eThe unguarded duck-type was introduced in 3768a75 and first shipped in v2.2.5 (September 2014). v2.2.4 and earlier used `Buffer.isBuffer` and are not affected. Every release from v2.2.5 through v6.15.3 contains the unguarded call.\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` (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 background job, the process exits, so the impact in that case depends on the application error handling rather than on qs.\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-703\", \"description\": \"CWE-703 Improper Check or Handling of Exceptional Conditions\"}]}], \"providerMetadata\": {\"orgId\": \"7ffcee3d-2c14-4c3e-b844-86c6a321a158\", \"shortName\": \"harborist\", \"dateUpdated\": \"2026-08-29T23:51:27.634Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-82417\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-31T17:08:24.074Z\", \"dateReserved\": \"2026-08-28T23:08:00.460Z\", \"assignerOrgId\": \"7ffcee3d-2c14-4c3e-b844-86c6a321a158\", \"datePublished\": \"2026-08-29T23:51:27.634Z\", \"assignerShortName\": \"harborist\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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