Google Chrome V8 Engine Type Confusion Remote Code Execution Vulnerability (CVE-2020-6418) Analysis and Mitigation Guide

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2020-6418) is a critical Type Confusion vulnerability in V8, the open-source high-performance JavaScript and WebAssembly engine used in Google Chrome. The root cause lies within the JIT (Just-In-Time) compiler, TurboFan, which fails to properly account for side-effects during the JSCreate phase. When optimizing JavaScript code, TurboFan assumes a specific object structure (Map). However, if a side-effect dynamically alters the object's map during creation, the compiler continues to access memory based on the outdated map assumption, resulting in type confusion.

2. Exploitation Mechanics & Attack Scenario

An attacker can trigger this vulnerability by crafting a malicious JavaScript payload that utilizes features like Proxy objects or Reflect.construct to execute user-defined callbacks during object instantiation. Within the callback, the attacker alters the layout of the object, forcing a map transition. Because TurboFan's optimization pipeline fails to track this side-effect, it generates machine code that accesses the object using incorrect offsets. This mismatch grants the attacker out-of-bounds read/write primitives in the V8 heap, which can be leveraged to bypass security mitigations, corrupt memory, and execute arbitrary shellcode.

3. Infrastructure & Business Impact

As a vulnerability listed in the CISA KEV catalog, CVE-2020-6418 has been actively exploited in the wild. Successful exploitation allows an attacker to compromise an endpoint system entirely when a user simply visits a compromised or malicious website. This serves as a highly effective initial access vector for corporate network intrusion, potentially leading to lateral movement, sensitive data exfiltration, ransomware deployment, and severe operational disruption.