CVE-2026-24888

The makerjs.extendObject function copies properties from source objects without proper validation, potentially exposing applications to security risks. The function lacks hasOwnProperty() checks and does not filter dangerous keys, allowing inherited properties and potentially malicious properties to be copied to target objects.

Details

The extendObject function iterates over source object properties using a for...in loop without:

1. Checking hasOwnProperty() to exclude inherited properties
2. Filtering dangerous keys (__proto__, constructor, prototype)
3. Validating property sources

Affected Code

File: https://github.com/microsoft/maker.js/blob/98cffa82a372ff942194c925a12a311253587167/packages/maker.js/src/core/maker.ts#L232-L241

PoC

const makerjs = require('makerjs');

const source = { __proto__: { name: 'Ravi', isAdmin: true } };
const target = { name: 'user' };
const result = makerjs.extendObject(target, source);

console.log(result.name);  // Ravi
console.log(result.isAdmin);   // true

Security Implications

1. Unexpected Behavior: Properties may appear on target objects but not be own properties, breaking hasOwnProperty() assumptions in security-sensitive code.

2. Security Bypass Risk: Code relying on hasOwnProperty() for validation could be bypassed.

3. Future Risk: Lack of dangerous key filtering (__proto__, constructor, prototype) exposes potential attack vectors.

Affected Use Cases

• Extending objects from user input or external APIs
• Merging options from untrusted sources

CVE-2026-24888 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.19.2); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-24888? CVE-2026-24888 is a medium-severity security vulnerability in makerjs (npm), affecting versions <= 0.19.1. It is fixed in 0.19.2.
2. How severe is CVE-2026-24888? CVE-2026-24888 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of makerjs are affected by CVE-2026-24888? makerjs (npm) versions <= 0.19.1 is affected.
4. Is there a fix for CVE-2026-24888? Yes. CVE-2026-24888 is fixed in 0.19.2. Upgrade to this version or later.
5. Is CVE-2026-24888 exploitable, and should I be worried? Whether CVE-2026-24888 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-24888 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-24888? Upgrade makerjs to 0.19.2 or later.