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Prototype Pollution


An application object, method or module can be overwritten with malicious logic due to the lack of validations and the nature of the JavaScript language.


  • Overwrite or pollute the behavior of existing methods in the application.
  • Lead to dangerous vulnerabilities suchs as XSS, SQLi, RCE, among others.


  • Implement integrity validations on the vulnerable objects.
  • Restrict and Discourage the use harmful properties such as proto in the system objects.


Authenticated attacker from the Internet.

Expected Remediation Time

⌚ 60 minutes.


Default score using CVSS 3.1. It may change depending on the context of the src.


  • Attack vector: N
  • Attack complexity: H
  • Privileges required: L
  • User interaction: N
  • Scope: U
  • Confidentiality: N
  • Integrity: L
  • Availability: N


  • Exploit code maturity: P
  • Remediation level: U
  • Report confidence: R


  • Vector string: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N/E:P/RL:U/RC:R
  • Score:
    • Base: 3.1
    • Temporal: 2.8
  • Severity:
    • Base: Low
    • Temporal: Low

Score 4.0

Default score using CVSS 4.0 . It may change depending on the context of the src.

Base 4.0

  • Attack vector: N
  • Attack complexity: H
  • Attack Requirements: N
  • Privileges required: L
  • User interaction: N
  • Confidentiality (VC): N
  • Integrity (VI): L
  • Availability (VA): N
  • Confidentiality (SC): N
  • Integrity (SI): N
  • Availability (SA): N

Threat 4.0

  • Exploit maturity: P

Result 4.0

  • Vector string: CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P
  • Score:
    • CVSS-BT: 1.3
  • Severity:
    • CVSS-BT: Low

Compliant code

There are no harmful functionalities on vulnerable objects

function modifyPrototype(moduleName, deleteMethod, newMethod) {
var newMod = new moduleName;

//Add new method to the object, without altering the original
newMod.${newMethod} = function() {
//Add functionality to object

return newMod;

Non compliant code

There are functionalities that can be overwritten due to insecure coding practices

function modifyPrototype(moduleName, deleteMethod, newMethod) {
// modifying the prototype of a module from within another function
var newMod = require(moduleName);
delete newMod[deleteMethod];
newMod.${newMethod} = function() {
// function body that modifies the original method

module.exports = newMod;



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