Prototype Poisoning Affecting qs package, versions <6.2.4 >=6.3.0 <6.3.3 >=6.4.0 <6.4.1 >=6.5.0 <6.5.3 >=6.6.0 <6.6.1 >=6.7.0 <6.7.3 >=6.8.0 <6.8.3 >=6.9.0 <6.9.7 >=6.10.0 <6.10.3



CVSS assessment made by Snyk's Security Team

    Threat Intelligence

    Exploit Maturity
    Proof of concept
    1.01% (84th percentile)

Do your applications use this vulnerable package?

In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.

Test your applications
  • Snyk ID SNYK-JS-QS-3153490
  • published 4 Dec 2022
  • disclosed 26 Nov 2022
  • credit BRAUN Nathanael, BRISSAUD Johan

How to fix?

Upgrade qs to version 6.2.4, 6.3.3, 6.4.1, 6.5.3, 6.6.1, 6.7.3, 6.8.3, 6.9.7, 6.10.3 or higher.


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

Affected versions of this package are vulnerable to Prototype Poisoning which allows attackers to cause a Node process to hang, processing an Array object whose prototype has been replaced by one with an excessive length value.

Note: In many typical Express use cases, an unauthenticated remote attacker can place the attack payload in the query string of the URL that is used to visit the application, such as a[__proto__]=b&a[__proto__]&a[length]=100000000.


Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its intended and legitimate users.

Unlike other vulnerabilities, DoS attacks usually do not aim at breaching security. Rather, they are focused on making websites and services unavailable to genuine users resulting in downtime.

One popular Denial of Service vulnerability is DDoS (a Distributed Denial of Service), an attack that attempts to clog network pipes to the system by generating a large volume of traffic from many machines.

When it comes to open source libraries, DoS vulnerabilities allow attackers to trigger such a crash or crippling of the service by using a flaw either in the application code or from the use of open source libraries.

Two common types of DoS vulnerabilities:

  • High CPU/Memory Consumption- An attacker sending crafted requests that could cause the system to take a disproportionate amount of time to process. For example, commons-fileupload:commons-fileupload.

  • Crash - An attacker sending crafted requests that could cause the system to crash. For Example, npm ws package

CVSS Scores

version 3.1
Expand this section


7.5 high
  • Attack Vector (AV)
  • Attack Complexity (AC)
  • Privileges Required (PR)
  • User Interaction (UI)
  • Scope (S)
  • Confidentiality (C)
  • Integrity (I)
  • Availability (A)
Expand this section


7.5 high
Expand this section

Red Hat

7.5 high