CVE-2026-8723: ### Summary `qs.stringify` throws `TypeError` when called with `arrayFormat: 'comma'` and `encodeValuesOnly: true` on an array containing `null` or…

### 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 `

Affected

CVSS provenance