CVE-2018-3720: Prototype Pollution in assign-deep

Prototype pollution vulnerabilities, like CVE-2018-3720, can have significant consequences. An attacker exploiting this flaw could inject malicious properties into the prototypes of JavaScript objects used throughout an application. This could lead to unexpected behavior, data corruption, or even denial-of-service. For example, an attacker might modify the prototype of Array to inject a malicious function that executes whenever an array is iterated over. The blast radius depends on how extensively assign-deep is used within the application and the sensitivity of the data being processed. While direct remote code execution is unlikely, the manipulation of object properties can be leveraged to bypass security checks or alter application logic.

1. Published2018-07-26
2. Modified2023-11-08
3. EPSS updated2026-04-02

The primary mitigation for CVE-2018-3720 is to upgrade the assign-deep library to version 0.4.7 or later. If upgrading is not immediately feasible due to compatibility concerns or breaking changes, consider implementing input validation and sanitization to prevent malicious data from being merged into objects. While not a complete solution, this can reduce the attack surface. Review your code for any instances where assign-deep is used to merge data from untrusted sources. There are no specific WAF rules or detection signatures readily available for this particular prototype pollution vulnerability, so focusing on code review and input validation is crucial. After upgrading, confirm the fix by running tests that specifically target object merging and property access to ensure no unexpected behavior arises.