CVE-2026-8723

CVE-2026-8723 is a medium-severity vulnerability with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-476.

Key facts

Description

### 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`).

Frequently asked questions

What is CVE-2026-8723?
### 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`).
How severe is CVE-2026-8723?
CVE-2026-8723 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.
Is CVE-2026-8723 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (27th percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-8723?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-8723 have an EU (EUVD) identifier?
Yes. CVE-2026-8723 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-30674.
When was CVE-2026-8723 published?
CVE-2026-8723 was published on 2026-05-17 and last updated on 2026-06-17.

References

Other CWE-476 (NULL Pointer Dereference) vulnerabilities

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