ljharb qs up to 6.15.1 lib/stringify.js null pointer dereference

Summaryinfo

A vulnerability identified as problematic has been detected in ljharb qs up to 6.15.1. Affected by this issue is some unknown functionality in the library lib/stringify.js. This manipulation causes null pointer dereference. This vulnerability is tracked as CVE-2026-8723. The attack is possible to be carried out remotely. No exploit exists. You should upgrade the affected component.

Detailsinfo

A vulnerability has been found in ljharb qs up to 6.15.1 and classified as problematic. Affected by this vulnerability is some unknown functionality in the library lib/stringify.js. The manipulation with an unknown input leads to a null pointer dereference vulnerability. The CWE definition for the vulnerability is CWE-476. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. As an impact it is known to affect availability. The summary by CVE is:

### Summary `qs.stringify` throws `TypeError` when called with `arrayFormat: 'comma'` and `encodeValuesOnly: true` on an array containing `null` or `undefined`. The throw is synchronous and not handled by any of qs's null-related options (`skipNulls`, `strictNullHandling`). ### Details In the comma + `encodeValuesOnly` branch, `lib/stringify.js:145` mapped the array through the raw encoder before joining: ```js obj = utils.maybeMap(obj, encoder); ``` `utils.encode` (`lib/utils.js:195`) reads `str.length` with no null guard, so a `null` or `undefined` element throws `TypeError`. `skipNulls` and `strictNullHandling` are both checked in the per-element loop below this line and never get a chance to run. Same class of bug as the filter-array path fixed in 0c180a4. The vulnerable shape of the comma + `encodeValuesOnly` branch was introduced in 4c4b23d ("encode comma values more consistently", PR #463, 2023-01-19), first released in v6.11.1. #### PoC ```js const qs = require('qs'); qs.stringify({ a: [null, 'b'] }, { arrayFormat: 'comma', encodeValuesOnly: true }); qs.stringify({ a: [undefined, 'b'] }, { arrayFormat: 'comma', encodeValuesOnly: true }); qs.stringify({ a: [null] }, { arrayFormat: 'comma', encodeValuesOnly: true }); // TypeError: Cannot read properties of null (reading 'length') // at encode (lib/utils.js:195:13) // at Object.maybeMap (lib/utils.js:322:37) // at stringify (lib/stringify.js:145:25) ``` #### Fix `lib/stringify.js:145`, applied in 21f80b3 on `main` and released as v6.15.2: ```diff - obj = utils.maybeMap(obj, encoder); + obj = utils.maybeMap(obj, function (v) { + return v == null ? v : encoder(v); + }); ``` `null` and `undefined` now pass through `maybeMap` unchanged and reach the `join(',')` step as-is. For `{ a: [null, 'b'] }` this produces `a=,b`, matching the non-`encodeValuesOnly` comma path (which already joins before encoding and produces `a=%2Cb` for the same input). Single-element `[null]` arrays still collapse via the existing `obj.join(',') || null` and remain subject to `skipNulls` / `strictNullHandling` in the main loop. ### Affected versions `>=6.11.1 <6.15.2` — fixed in v6.15.2. The vulnerable code shape was introduced in 4c4b23d and first shipped in v6.11.1. Earlier versions — including all of 6.7.x, 6.8.x, 6.9.x, 6.10.x, and 6.11.0 — implemented the comma + `encodeValuesOnly` path differently (joining before encoding) and are not affected. Empirically verified across released versions. ### Impact Application code that calls `qs.stringify` with both `arrayFormat: 'comma'` and `encodeValuesOnly: true` (both non-default) on input that may contain a `null` or `undefined` array element will throw synchronously instead of producing a query string. In a typical Node.js HTTP framework (Express, Fastify, Koa, hapi) the sync throw is caught by the framework's error boundary and the affected request returns a 500; the worker process does not exit and subsequent requests are unaffected. The "kills the worker process" framing applies only to call sites outside a request-handler error boundary (background jobs, startup paths, stream pipelines) or to deployments with framework error handling explicitly disabled. The vulnerable input is a `null` or `undefined` entry inside an array; this is reachable from JSON request bodies or from application code constructing arrays from user input, but not from standard HTML form submissions (which produce strings or omitted fields, not literal `null`).

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-8723 since 05/16/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 315208 (Linux Distros Unpatched Vulnerability : CVE-2026-8723), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.15.2 eliminates this vulnerability. Applying the patch 21f80b33e5c8b3f7eba1034fff0da4a4a37a1d41 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at CNNVD (CNNVD-202605-3961), Tenable (315208) and CERT Bund (WID-SEC-2026-2118). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Affected

• IBM App Connect Enterprise

Productinfo

Vendor

• ljharb

Name

• qs

Version

• 6.15.0
• 6.15.1

License

• open-source

Website

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

CPE 2.3info

• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Discussion