CVE-2026-24888: Maker.js Prototype Pollution Flaw Exposes Developer Toolchains to Silent Logic Manipulation

CVE-2026-24888 — Maker.js Prototype Pollution Vulnerability

Vulnerability Overview

CVE ID: CVE-2026-24888
Affected Component: Maker.js
Affected Function: makerjs.extendObject
Vulnerability Class: Prototype Pollution
Severity: Medium
CVSS v3.1 Base Score: 6.5
Attack Vector: Network
Privileges Required: None
User Interaction: None
Exploit Maturity: Conceptually exploitable; no widely published weaponized exploit observed
Impact Scope: Application logic manipulation, security control bypass, and potential vulnerability chaining

Official Patch / Upgrade Link (only official link):
👉 https://github.com/microsoft/maker.js/security/advisories/GHSA-2cp6-34r9-54xx

Description of the Vulnerability

A prototype pollution vulnerability was identified in Maker.js versions up to and including 0.19.1. The issue resides in the internal utility function extendObject, which was designed to merge properties from one object into another.

During this merging process, object properties were copied without validation, without ownership checks, and without filtering special JavaScript meta-properties. As a result, properties such as __proto__, constructor, and prototype could be injected into destination objects.

Because JavaScript objects inherit from prototypes, modification of these prototype properties allowed attackers to influence the behavior of unrelated objects across the application runtime. This condition is known as prototype pollution.

The vulnerability was corrected in Maker.js version 0.19.2, where defensive checks were introduced to prevent unsafe property propagation.

Technical Root Cause

The vulnerability occurred due to the following conditions:

Properties were copied using generic iteration logic
hasOwnProperty() validation was not enforced
Dangerous keys capable of mutating object prototypes were not blocked
Nested objects were processed without sanitization

This allowed attacker-controlled input objects to modify global or shared object prototypes indirectly.

Impact and Risk Assessment

While the vulnerability does not directly result in remote code execution on its own, the following impacts were observed as possible outcomes:

Application logic manipulation
Security validation bypass
Privilege flag injection
Unexpected behavior across unrelated components
Increased risk of follow-on exploitation when chained with other vulnerabilities

In environments where Maker.js is used in backend services, automation pipelines, or developer tooling that processes untrusted input, the risk is elevated.

Exploitation Scenario (Educational Purpose Only)

To exploit this vulnerability, the following conditions must be met:

User-controlled input must reach extendObject or a wrapper function calling it
The input must be treated as an object without sanitization
The merged object must later influence logic or security decisions

Example Educational Payload

{
  "__proto__": {
    "isPrivileged": true
  }
}

When processed by the vulnerable function, this payload could result in isPrivileged being present on all objects inheriting from Object.prototype.

Proof-of-Concept Status

No confirmed public exploit toolkit is currently circulating
No known automated exploit frameworks target this CVE specifically
The vulnerability pattern is well understood and easily testable

Due to the simplicity of prototype pollution mechanics, exploitation feasibility should be considered high if a vulnerable code path exists.

Detection and Identification

Indicators of Attempted Exploitation

The following patterns may indicate exploitation attempts:

Incoming JSON containing:
- __proto__
- constructor
- prototype
Unexpected boolean or privilege-style properties appearing across objects
Logic behaving inconsistently without corresponding code changes

Runtime Verification Checks

A quick defensive runtime check can be implemented to detect pollution:

if (Object.prototype.hasOwnProperty("isPrivileged")) {
  // Prototype pollution suspected
}

If unexpected properties are found on Object.prototype, immediate investigation is recommended.

Log Sources to Monitor

The following log sources should be monitored closely:

Web server access logs (request bodies where possible)
Application request parsing logs
Debug logs capturing object merges or configuration loading
Dependency and build logs identifying Maker.js versions
Runtime anomaly or integrity monitoring systems

Detection Rules

IDS / IPS Rule

Detect JSON payloads containing "__proto__", "constructor", or "prototype"
within HTTP request bodies.

SIEM Rule Logic

Condition:
  RequestBody contains "__proto__"
  OR RequestBody contains "constructor"
  OR RequestBody contains "prototype"
Severity: Medium
Action: Alert + Log Request Context

Behavioral Rule

Alert when inherited properties appear on application objects that were never explicitly defined
Alert when application state changes without corresponding configuration updates

Mitigation and Remediation

Immediate Actions

Upgrade Maker.js to version 0.19.2 or later
Redeploy all applications using patched dependencies
Confirm transitive dependencies do not bundle older versions

Temporary Mitigation

Sanitize all incoming objects
Explicitly delete dangerous keys before processing
Enforce strict allowlists for object merging

Example sanitization logic:

function sanitize(input) {
  if (typeof input !== "object" || input === null) return input;
  delete input.__proto__;
  delete input.constructor;
  delete input.prototype;
  for (const key in input) {
    sanitize(input[key]);
  }
  return input;
}

MITRE Classification

CWE: CWE-1321 — Improperly Controlled Modification of Object Prototype Attributes
Attack Pattern: Prototype Pollution

Security Best Practices Going Forward

Avoid generic object merging with untrusted data
Prefer structured schema validation
Use immutable configuration objects
Monitor prototype integrity at runtime
Include prototype pollution checks in security testing

Final Takeaway

CVE-2026-24888 is a classic but impactful prototype pollution vulnerability caused by unsafe object property copying in Maker.js. While the severity is classified as medium, the real-world impact depends heavily on how and where the library is used.

The issue has been fully resolved by the vendor, and upgrading remains the definitive fix. Detection and monitoring controls should be implemented to identify both attempted and successful exploitation, particularly in environments where untrusted input is processed.