Windows Kernel Information Disclosure Vulnerability (CVE-2021-31955) Analysis and Mitigation Guide

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2021-31955) is an information disclosure flaw in the Windows Kernel arising from improper exposure of sensitive system information or structure addresses to user-mode processes (CWE-497). The root cause lies in the kernel's failure to properly sanitize or mask kernel pointers returned during specific system calls or API operations, allowing local unprivileged users to read sensitive kernel memory layouts.

2. Exploitation Mechanics & Attack Scenario

An attacker with local access executes a specially crafted application designed to invoke the vulnerable kernel functions. By parsing the returned memory buffers, the application extracts the precise virtual memory addresses of kernel structures. While this vulnerability does not directly grant remote code execution or privilege escalation on its own, it effectively neutralizes Kernel Address Space Layout Randomization (KASLR). Attackers leverage this leaked address space layout to construct highly reliable exploit chains, pairing it with other kernel vulnerabilities (such as CVE-2021-31956) to achieve full SYSTEM privileges.

3. Infrastructure & Business Impact

CVE-2021-31955 is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating active exploitation in the wild by advanced persistent threat (APT) actors. In an enterprise environment, leaving this vulnerability unpatched allows internal threat actors or compromised low-privilege accounts to escalate privileges, compromise domain controllers, deploy ransomware, and establish persistent administrative control over critical infrastructure.