qs
CVE-2025-15284
MEDIUM
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessSend crafted bracket-notation query string
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ExploitBypass arrayLimit via repeated a[] params
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ImpactExhaust server memory (availability DoS)
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A05:2025 - Injection
ASVS 5.0
V2 - Validation and Business Logic Input validation, allowlisting
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| Exploitation Conditions | Exploitation requires that the target application (1) uses qs to parse attacker-controlled query strings, (2) has array parsing enabled (parseArrays, the default), and critically (3) has explicitly set parameterLimit to a very high value well above the default of 1000. The default parameterLimit of 1000 caps the total parsed parameters and therefore the number of bracket-notation (a[]=value) elements, neutralizing the DoS regardless of arrayLimit. The primary limiting factor is thus this non-default configuration prerequisite; no authentication or user interaction is required once that config is in place, and the impact is bounded to low memory/availability pressure rather than code execution. |
| Impact | This is a low-to-moderate risk issue that the vendor itself downgraded. The input CVSS 4.0 vector (AV:N/AC:L/AT:P/PR:N/UI:N) scores 6.3 and includes AT:P (attack requirements), correctly signaling that exploitation is not against default configurations - the VA:L/SA:L impacts confirm only a low availability effect, no confidentiality or integrity impact. EPSS is low at 0.45% (37th percentile), consistent with a consistency bug rather than a mass-exploited flaw. POC code exists (in the GHSA advisory) but there is NO CISA KEV listing, so POC availability must not be conflated with active exploitation. The signals are internally consistent and align with the advisory's own 'severity reduced' note: the default parameterLimit of 1000 already caps bracket-notation array growth, so the DoS is only practically reachable when an operator has explicitly raised parameterLimit far above the default. Verdict: a real but conditional, low-priority availability bug - high CVSS reach (ubiquitous package, network vector) tempered by a hard configuration prerequisite that the AT:P metric and low EPSS both reflect. |
| Exploit ScenarioDerived | An attacker sends an HTTP request to a Node.js service that parses untrusted query strings with qs configured with a very high (non-default) parameterLimit. Using bracket notation (a[]=1&a[]=2&...), the attacker bypasses the arrayLimit cap and forces qs to allocate an oversized array/object, consuming excess server memory. Publicly available PoC exists in the GHSA advisory, but with the default parameterLimit of 1000 the impact is negligible. |
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Alert meAnalysisAIv1 – Oct 14, 2026
Memory and availability pressure in the npm package qs (versions before 6.14.1) stems from an input-validation gap where the arrayLimit parse option is enforced for indexed array notation (a[0]=1) but not for bracket notation (a[]=1), letting attackers control how many array elements are materialized for a single key from an attacker-supplied query string. Exploitation requires a non-default configuration: the application must use qs to parse attacker-controlled query strings with parseArrays enabled (the default) and, critically, parameterLimit explicitly raised well above its default of 1000, because parameterLimit independently caps total parsed parameters and neutralizes the issue under default settings. Unauthenticated remote attackers face no user interaction, but impact is bounded to low availability/memory pressure rather than code execution; publicly available exploit code exists (PoC in vendor advisory GHSA-6rw7-vpxm-498p), a vendor patch is available in qs 6.14.1, and EPSS is only 0.45% (37th percentile), consistent with the vendor's own severity downgrade.
RemediationAI
Upgrade to qs 6.14.1 or later (for example npm install qs@^6.14.1), which is the vendor-released fix referenced by GHSA-6rw7-vpxm-498p and commit 3086902ecf7f088d0d1803887643ac6c03d415b9. If upgrading immediately is not possible, the most effective compensating control is to set parameterLimit explicitly to the default 1000 or lower, since it caps total parsed parameters and thus bounds bracket-notation expansion - the trade-off is that legitimate requests or form bodies with more than that many parameters will be truncated or rejected. Applications that do not need array parsing can set parseArrays: false, which stops bracket-notation arrays from being built at all, but this changes parsed output into plain key/value pairs and may break downstream consumers expecting arrays. Do not raise arrayLimit or parameterLimit to accommodate large payloads, as that restores the vulnerable condition; where very large query strings are unavoidable, validate and cap request body/query size at the reverse proxy or framework layer (for example limiting URL length or max parameter counts in Express/Koa middleware), accepting that this rejects unusually large but legitimate requests. Note that the patched behavior converts over-limit arrays into numeric-keyed objects rather than arrays, so teams using permissive array settings should test consumers after upgrading. Vendor advisories to consult: https://github.com/ljharb/qs/security/advisories/GHSA-6rw7-vpxm-498p and the patch commit https://github.com/ljharb/qs/commit/3086902ecf7f088d0d1803887643ac6c03d415b9.
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 1 package in npm
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Technical ContextAI · show details
qs is a widely used Node.js library that parses URL query strings and form-encoded bodies into nested JavaScript objects and arrays. It supports two array notations: indexed notation such as a[0]=1 and bracket notation such as a[]=1. The arrayLimit option is intended to bound how many elements a single key can expand into, and indexed notation honored it via a check like index <= options.arrayLimit in lib/parse.js; the bracket-notation branch, however, built arrays through utils.combine([], leaf) (lib/parse.js around line 159) with no arrayLimit validation at all, so bracket notation could exceed the configured limit. This is a classic CWE-20 improper input validation / inconsistent enforcement defect rather than a memory-safety bug, since the resulting object is simply larger than the option promises. The fix (commit 3086902ecf7f088d0d1803887643ac6c03d415b9) threads arrayLimit into utils.combine, tracks over-limit results with a side-channel registry (markOverflow/isOverflow/getMaxIndex), and converts arrays that exceed the limit into numeric-keyed objects that still preserve every value; because arrayLimit defaults to a modest value and parameterLimit defaults to 1000 (each a[]=value consumes one parameter slot), the original advisory's claimed 10,000-element blow-up is not reachable with default options. The CPE cpe:2.3:a:qs_project:qs:*:*:*:*:*:node.js:*:*: within the Node.js platform target identifies the npm-distributed package, and note that the attached 'Information Disclosure' tag is inconsistent with the assessed availability-only impact - there is no confidentiality impact in the assessed vector.
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Severity by source
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:L
Remote unauthenticated (AV:N/PR:N) but AC:H because meaningful DoS requires a non-default high parameterLimit; only low availability impact, no C/I impact.
Primary rating from Vendor (7ffcee3d-2c14-4c3e-b844-86c6a321a158).
CVSS VectorVendor: 7ffcee3d-2c14-4c3e-b844-86c6a321a158
DescriptionCVE.org
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.
Blast Radius
ecosystem impact- 253 npm packages depend on qs (79 direct, 175 indirect)
Ecosystem-wide dependent count for version 6.14.1.
Threat Intelligence Overview
NVD
CVE.org
EPSS
GitHub
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Affected Products (CPE)CVE.org
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Comma-split value parsing in the qs npm library (versions 6.14.2 through 6.15.3) bypasses the caller-configured `arrayLi
### Summary The `arrayLimit` option in qs does not enforce limits for comma-separated values when `comma: true` is enabl
the web framework using ljharb's qs module older than v6.3.2, v6.2.3, v6.1.2, and v6.0.4 is vulnerable to a DoS. Rated h
Query string parameter injection in the npm qs library: when an application calls qs.stringify with the non-default opti
Exploit-DB