Find, fix and prevent vulnerabilities in your code.

Overview

qs is a querystring parser that supports nesting and arrays, with a depth limit.

Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling via improper enforcement of the arrayLimit option in bracket notation parsing. An attacker can exhaust server memory and cause application unavailability by submitting a large number of bracket notation parameters - like a[]=1&a[]=2 - in a single HTTP request.

PoC

const qs = require('qs');
const attack = 'a[]=' + Array(10000).fill('x').join('&a[]=');
const result = qs.parse(attack, { arrayLimit: 100 });
console.log(result.a.length);  // Output: 10000 (should be max 100)

Remediation

Upgrade qs to version 6.14.1 or higher.

References

• GitHub Commit

Overview

qs is a querystring parser that supports nesting and arrays, with a depth limit.

Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling via the parseArrayValue function when the comma option is in use. An attacker can exhaust system memory by submitting a parameter containing a large number of comma-separated values, resulting in the allocation of excessively large arrays.

Note: This is only exploitable if the comma option is explicitly set to true. arrayLimit is properly enforced for index and bracket notation.

PoC

const qs = require('qs');

const payload = 'a=' + ','.repeat(25);  // 26 elements after split (bypasses arrayLimit: 5)
const options = { comma: true, arrayLimit: 5, throwOnLimitExceeded: true };

try {
  const result = qs.parse(payload, options);
  console.log(result.a.length);  // Outputs: 26 (bypass successful)
} catch (e) {
  console.log('Limit enforced:', e.message);  // Not thrown
}

Remediation

Upgrade qs to version 6.14.2 or higher.

References

• GitHub Commit