CVE-2025-15284: arrayLimit bypass in bracket notation allows DoS via memory exhaustion

Vulnerability summary

CVE-2025-15284 is a medium (CVSS 6.3) Improper Input Validation vulnerability in qs_project qs. EPSS estimates a 0.45% chance of exploitation in the next 30 days, higher than 39.1% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 29-12-2025
   PublishedVulnerability first disclosed.
2. 10-02-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-20Improper Input ValidationThe product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.