ljharb qs up to 6.15.x Buffer Detection lib/utils.js utils.isBuffer obj uncaught exception

Summaryinfo

A vulnerability was found in ljharb qs up to 6.15.x. It has been declared as problematic. The impacted element is the function utils.isBuffer of the file lib/utils.js of the component Buffer Detection. The manipulation of the argument obj results in input validation. This vulnerability is cataloged as CVE-2026-82417. The attack may be launched remotely. There is no exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, was found in ljharb qs up to 6.15.x. Affected is the function utils.isBuffer of the file lib/utils.js of the component Buffer Detection. The manipulation of the argument obj with an unknown input leads to a input validation vulnerability. CWE is classifying the issue as CWE-248. An exception is thrown from a function, but it is not caught. This is going to have an impact on availability. CVE summarizes:

### 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.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-82417 since 08/29/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Technical details are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 341603 (Linux Distros Unpatched Vulnerability : CVE-2026-82417), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.16.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (341603). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Vendor

• ljharb

Name

• qs

Version

• 6.0
• 6.1
• 6.2
• 6.3
• 6.4
• 6.5
• 6.6
• 6.7
• 6.8
• 6.9
• 6.10
• 6.11
• 6.12
• 6.13
• 6.14
• 6.15

Website

• Product: https://github.com/ljharb/qs/

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