CVE-2025-15284
Fix: ljharb/qs@3086902CVE-2025-15284 is a Improper Input Validation vulnerability in qs. O3 Security confirms whether CVE-2025-15284 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
arrayLimit bypass in bracket notation allows DoS via memory exhaustion
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
qsnpmDescription
Improper Input Validation vulnerability in qs (parse modules) allows HTTP DoS.This issue affects qs: < 6.14.1.
Summary
The arrayLimit option in qs did not enforce limits for bracket notation (a[]=1&a[]=2), only for indexed notation (a[0]=1). This is a consistency bug; arrayLimit should apply uniformly across all array notations.
Note: The default parameterLimit of 1000 effectively mitigates the DoS scenario originally described. With default options, bracket notation cannot produce arrays larger than parameterLimit regardless of arrayLimit, because each a[]=valueconsumes one parameter slot. The severity has been reduced accordingly.
Details
The arrayLimit option only checked limits for indexed notation (a[0]=1&a[1]=2) but did not enforce it for bracket notation (a[]=1&a[]=2).
Vulnerable code (lib/parse.js:159-162):
if (root === '[]' && options.parseArrays) { obj = utils.combine([], leaf); // No arrayLimit check }
Working code (lib/parse.js:175):
else if (index <= options.arrayLimit) { // Limit checked here obj = []; obj[index] = leaf; }
The bracket notation handler at line 159 uses utils.combine([], leaf) without validating against options.arrayLimit, while indexed notation at line 175 checks index <= options.arrayLimit before creating arrays.
PoC
const qs = require('qs'); const result = qs.parse('a[]=1&a[]=2&a[]=3&a[]=4&a[]=5&a[]=6', { arrayLimit: 5 }); console.log(result.a.length); // Output: 6 (should be max 5)
Note on parameterLimit interaction: The original advisory's "DoS demonstration" claimed a length of 10,000, but parameterLimit (default: 1000) caps parsing to 1,000 parameters. With default options, the actual output is 1,000, not 10,000.
Impact
Consistency bug in arrayLimit enforcement. With default parameterLimit, the practical DoS risk is negligible since parameterLimit already caps the total number of parsed parameters (and thus array elements from bracket notation). The risk increases only when parameterLimit is explicitly set to a very high value.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | qs | all versions | 6.14.1 |
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 6.14.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-15284 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-2025-15284 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-2025-15284. 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-2025-15284 in your dependencies?
O3 detects CVE-2025-15284 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.