CVE-2026-82417

Estado: Pendiente de análisisMedia (6.3)—

### 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.

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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

// 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

```

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.

Detalles técnicos trazas, registros y código del informe original

var qs = require("qs");

qs.stringify(qs.parse("x[constructor][isBuffer]=y", { plainObjects: true }));

qs.stringify(JSON.parse("{\"a\":{\"constructor\":{\"isBuffer\":\"x\"}}}"));

- return !!(obj.constructor && obj.constructor.isBuffer && obj.constructor.isBuffer(obj));

+ return !!(obj.constructor && typeof obj.constructor.isBuffer === "function" && obj.constructor.isBuffer(obj));

CVSS

Versión: 4.0
Vector: 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Puntuación base: 6.3

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.42%
Percentil entre todas las CVEs puntuadas: 34
Fecha de la puntuación: 6/10/2026

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

Tecnologías afectadas (3)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Express — Express^AI Openjsf — Body-parser^AI QS — QS^AI

CWE

CWE-248, CWE-703

Referencias

JSON original (NVD)

Mostrar

{
  "id": "CVE-2026-82417",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-82417",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-08-31T17:07:54.823942Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 5.3,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "LOW",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 1.4,
        "exploitabilityScore": 3.9
      }
    ],
    "cvssMetricV40": [
      {
        "type": "Secondary",
        "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
        "cvssData": {
          "Safety": "NOT_DEFINED",
          "version": "4.0",
          "Recovery": "NOT_DEFINED",
          "baseScore": 6.3,
          "Automatable": "NOT_DEFINED",
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
          "exploitMaturity": "NOT_DEFINED",
          "providerUrgency": "NOT_DEFINED",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "attackRequirements": "PRESENT",
          "privilegesRequired": "NONE",
          "subIntegrityImpact": "NONE",
          "vulnIntegrityImpact": "NONE",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "vulnAvailabilityImpact": "LOW",
          "availabilityRequirement": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "subConfidentialityImpact": "NONE",
          "vulnConfidentialityImpact": "NONE",
          "confidentialityRequirement": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "vulnerabilityResponseEffort": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED"
        }
      }
    ]
  },
  "affected": [
    {
      "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
      "affectedData": [
        {
          "repo": "https://github.com/ljharb/qs",
          "vendor": "ljharb",
          "product": "qs",
          "versions": [
            {
              "status": "affected",
              "version": "2.2.5",
              "lessThan": "6.16.0",
              "versionType": "semver"
            }
          ],
          "packageName": "qs",
          "collectionURL": "https://npmjs.com/qs",
          "defaultStatus": "unaffected"
        }
      ]
    }
  ],
  "published": "2026-08-30T00:16:34.657",
  "references": [
    {
      "url": "https://github.com/ljharb/qs/commit/e83d321ffafb38cf210683ac31714fce6ce1c6c6",
      "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158"
    },
    {
      "url": "https://github.com/ljharb/qs/security/advisories/GHSA-4mjr-xmp4-gh2g",
      "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158"
    },
    {
      "url": "https://github.com/ljharb/qs/security/advisories/GHSA-4mjr-xmp4-gh2g",
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0"
    }
  ],
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "7ffcee3d-2c14-4c3e-b844-86c6a321a158",
      "description": [
        {
          "lang": "en",
          "value": "CWE-248"
        },
        {
          "lang": "en",
          "value": "CWE-703"
        }
      ]
    }
  ],
  "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 && obj.constructor.isBuffer && obj.constructor.isBuffer(obj));\n\n\n\n+ return !!(obj.constructor && typeof obj.constructor.isBuffer === \"function\" && 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`>=2.2.5 <6.16.0`, 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."
    }
  ],
  "lastModified": "2026-09-03T18:00:36.970",
  "sourceIdentifier": "7ffcee3d-2c14-4c3e-b844-86c6a321a158"
}