CVE-2026-82417

A flaw was found in qs. The qs.stringify function, responsible for serializing objects, does not properly validate the isBuffer property of an object's constructor before attempting to invoke it. An unauthenticated attacker can provide specially crafted input that, when processed and then serialized by qs.stringify, triggers a TypeError. This vulnerability can lead to a Denial of Service (DoS), causing affected applications to return a 500 error or, in certain scenarios, terminate the application process.

A denial of service vulnerability was found in the qs package for Node.js. The stringify function does not verify that constructor.isBuffer is callable before invoking it. An attacker who can influence object shape, for example through query parameters parsed with allowPrototypes: true as Express 4 does by default, can cause qs.stringify to throw a TypeError when that data is re-serialized. In typical Node.js HTTP frameworks the error is caught per request and returns HTTP 500. In code paths without an error boundary, such as async handlers or background jobs, the process may exit.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

If an immediate upgrade to qs 6.16.0 is not feasible, avoid re-serializing attacker-influenced parsed query or body objects with qs.stringify. Where qs.parse is used directly, set allowPrototypes: false unless prototype keys are required. For Express applications, review whether the default query parser configuration is necessary. Wrapping qs.stringify calls in try/catch can limit impact to individual requests.