Google Chrome Blink Use-After-Free Vulnerability (CVE-2021-21193) Technical Advisory

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2021-21193) is a Use-After-Free (UAF) flaw residing in the Blink rendering engine of Google Chrome. It occurs when the Blink engine fails to properly clear or nullify pointers to memory objects in the heap after they have been deleted or deallocated during DOM tree manipulation or style resolution. Consequently, the browser attempts to reuse these dangling pointers, leading to heap corruption.

2. Exploitation Mechanics & Attack Scenario

An attacker can exploit this vulnerability by hosting a specially crafted HTML page containing malicious DOM structures or CSS/JS payloads. When a victim visits the malicious page, the Blink engine processes the malformed content, triggering premature deallocation of a specific object. The attacker then utilizes heap grooming techniques to fill the freed memory slot with controlled data. When the engine subsequently references the stale pointer, control flow is hijacked, allowing arbitrary code execution within the context of the renderer process.

3. Infrastructure & Business Impact

As this vulnerability is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, it represents a highly active threat vector. Successful exploitation allows remote code execution (RCE) on the user's endpoint. If chained with a sandbox escape vulnerability, the attacker can compromise the underlying operating system, leading to unauthorized access to sensitive corporate data, lateral movement within the internal network, and potential ransomware deployment.