CVE-2026-8723
Fix: ljharb/qs@21f80b3CVE-2026-8723 is a NULL Pointer Dereference vulnerability in qs. O3 Security confirms whether CVE-2026-8723 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
qs.stringify crashes on null/undefined entries in comma-format arrays under encodeValuesOnly
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-8723.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
qsnpmDescription
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:
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
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:
- 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).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | qs | ≥ 6.11.1&&< 6.15.2 | 6.15.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for qs. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update qs to 6.15.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-8723 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-8723 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-8723. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-8723 in your dependencies?
O3 detects CVE-2026-8723 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.