Windows ALPC (Advanced Local Procedure Call) Use-After-Free Elevation of Privilege Vulnerability (CVE-2023-21674) Analysis and Mitigation Guide

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2023-21674) is a Use-After-Free (UAF) flaw residing in the Windows Advanced Local Procedure Call (ALPC) framework, which is the core inter-process communication (IPC) mechanism of the Windows kernel. The root cause lies in improper lifecycle management of ALPC port and message objects. Under specific error conditions or malformed requests, the kernel fails to properly nullify pointers to memory blocks that have already been freed, leaving dangling pointers active in kernel space.

2. Exploitation Mechanics & Attack Scenario

To exploit this vulnerability, an attacker must first gain local execution capabilities on the target system with low or medium integrity privileges. The attacker then transmits specially crafted ALPC messages to trigger the release of a specific kernel object. By leveraging heap spraying techniques, the attacker reclaims the freed memory space with controlled malicious payloads. When the kernel subsequently references the dangling pointer, it executes attacker-controlled virtual function tables (vtables), enabling sandbox escape and arbitrary code execution with SYSTEM privileges.

3. Infrastructure & Business Impact

As this vulnerability is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, it has been actively exploited in the wild by threat actors. When chained with a web browser or document reader Remote Code Execution (RCE) vulnerability, this Elevation of Privilege (EoP) allows attackers to achieve full system compromise without user interaction, potentially leading to lateral movement, ransomware deployment, and severe business disruption.