Google Chrome V8 Engine Heap Buffer Overflow Vulnerability (CVE-2021-21148) Technical Advisory

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2021-21148) is a critical heap buffer overflow (CWE-787) residing in the V8 JavaScript and WebAssembly engine of Google Chrome. The root cause lies in improper boundary validation or size calculation during memory allocation within V8, allowing data to be written outside the bounds of the allocated heap buffer.

2. Exploitation Mechanics & Attack Scenario

An attacker can exploit this vulnerability by hosting a specially crafted HTML page containing malicious JavaScript code. When a victim visits the page, the V8 engine processes the malicious script (often leveraging array transfer bypass techniques), leading to out-of-bounds memory writes. This corrupts adjacent heap structures, enabling the attacker to bypass browser security controls and potentially execute arbitrary code within the context of the browser sandbox.

3. Infrastructure & Business Impact

As a zero-day vulnerability actively exploited in the wild (listed in CISA KEV), the business risk is extremely high. Successful exploitation on an enterprise endpoint can lead to initial access for threat actors, facilitating lateral movement, sensitive data exfiltration, or ransomware deployment across the corporate network.