Microsoft Windows splwow64 Local Privilege Escalation Vulnerability (CVE-2020-0986) Technical Analysis and Hardening Guide

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2020-0986) is a Local Privilege Escalation (LPE) vulnerability caused by the Windows kernel failing to properly handle objects in memory, leading to an Out-of-bounds Write (CWE-787). Specifically, the flaw resides within the Local Procedure Call (LPC) port communication handling of splwow64.exe (the printer driver host for 32-bit applications running on 64-bit Windows). The process fails to validate pointer offsets passed via LPC messages, allowing an attacker to write arbitrary data to arbitrary memory addresses (Write-What-Where primitive) within the context of the splwow64.exe process.

2. Exploitation Mechanics & Attack Scenario

To exploit this vulnerability, an attacker must first gain local access to the target system with low or medium integrity privileges. The attacker then establishes a connection to the LPC port exposed by splwow64.exe. By sending a specially crafted LPC message containing malicious pointers to functions like GdiPrinterThunk, the attacker bypasses pointer validation checks. This allows the attacker to overwrite critical memory structures or function pointers inside splwow64.exe, hijacking the execution flow to run arbitrary payloads with elevated SYSTEM privileges.

3. Infrastructure & Business Impact

As a vulnerability listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, CVE-2020-0986 has been actively exploited in the wild by advanced persistent threat (APT) actors. In an enterprise environment, this vulnerability is highly valuable for lateral movement and privilege escalation after an initial foothold is established. Compromising SYSTEM privileges allows attackers to disable endpoint detection and response (EDR) agents, dump credentials from LSASS memory, and compromise the entire Active Directory domain, posing a severe threat to business operations.