qs: Denial of Service via Attacker Controlled isBuffer

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.3 · 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 · score source

EPSS

• CVE-2026-82417: 0.40% estimated exploitation activity in the next 30 days; percentile 33.85 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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: utils.isBuffer (lib/utils.js:327-333) invokes obj.constructor.isBuffer without verifying it is callable: constructor and isBuffer are ordinary keys. qs.parse with…

Published by the source

2 Sep 2026, 14:45 UTC

Last modified by the source

2 Sep 2026, 14:45 UTC

Source last checked

26 Oct 2026, 13:02 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-4mjr-xmp4-gh2g

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# Patch Next advisory brief: CVE-2026-82417

Advisory: qs: Denial of Service via Attacker Controlled isBuffer
IDs: CVE-2026-82417, GHSA-4mjr-xmp4-gh2g
Record: https://patchnext.com/advisories/cve-2026-82417 (revision 1, source checked 26 Oct 2026, 13:02 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: qs 6.16.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm qs: affected >= 2.2.5, < 6.16.0; fixed in 6.16.0

## Suggested inspection (read-only)
- `npm ls qs --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on qs.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-4mjr-xmp4-gh2g (GitHub-reviewed advisory GHSA-4mjr-xmp4-gh2g lists affected ranges: npm qs >=2.2.5 <6.16.0)

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