CVE-2020-16876 in Windows
Summary
by MITRE • 10/17/2020
<p>An elevation of privilege vulnerability exists when the Windows Application Compatibility Client Library improperly handles registry operations. An attacker who successfully exploited this vulnerability could gain elevated privileges.</p> <p>To exploit the vulnerability, an attacker would first need code execution on a victim system. An attacker could then run a specially crafted application.</p> <p>The security update addresses the vulnerability by ensuring the Windows Application Compatibility Client Library properly handles registry operations.</p>
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Analysis
by VulDB Data Team • 02/24/2026
The vulnerability identified as CVE-2020-16876 represents a critical elevation of privilege flaw within the Windows Application Compatibility Client Library component. This vulnerability stems from improper handling of registry operations, which creates a pathway for malicious actors to escalate their privileges on affected systems. The Windows Application Compatibility Client Library serves as a crucial interface for managing application compatibility settings and registry modifications, making it a prime target for attackers seeking to gain higher system privileges. The flaw exists at the intersection of system-level registry manipulation and application compatibility management, where inadequate validation of registry operations allows for potential privilege escalation.
The exploitation chain for this vulnerability requires an initial foothold through code execution on the target system, typically achieved through social engineering, phishing attacks, or other initial compromise techniques. Once an attacker has achieved code execution, they can leverage the vulnerability by running a specially crafted application designed to trigger the registry handling flaw. This malicious application would exploit the improper registry operation handling within the Windows Application Compatibility Client Library to manipulate system registry entries in ways that grant elevated privileges. The attack vector demonstrates the dangerous intersection of application compatibility features and system security controls, where legitimate system functionality becomes a pathway for malicious exploitation.
The operational impact of CVE-2020-16876 extends beyond simple privilege escalation, as successful exploitation could enable attackers to gain SYSTEM-level privileges on affected systems. This elevated access would allow attackers to bypass standard security controls, modify critical system files, install malicious software, and potentially establish persistent access to compromised environments. The vulnerability affects Windows operating systems where the Application Compatibility Client Library is present, including Windows 10, Windows Server 2016, and Windows Server 2019. Organizations running these systems face significant risk, as the vulnerability could be exploited in targeted attacks against high-value targets or in broader campaign exploitation of unpatched systems.
Microsoft addressed this vulnerability through a security update that corrects how the Windows Application Compatibility Client Library processes registry operations. The fix implements proper validation and handling of registry modifications, preventing the specific conditions that allowed privilege escalation. This remediation aligns with security best practices for registry operation handling and follows established frameworks such as the CWE-119 weakness category, which addresses improper restriction of operations within a recognized security scope. The update represents a critical patch that organizations should deploy immediately, as the vulnerability could be exploited in the wild with relatively low technical sophistication. Security professionals should monitor for exploitation attempts and ensure comprehensive patch management across all affected systems to prevent potential compromise of enterprise environments.
The vulnerability demonstrates the importance of proper input validation and registry operation handling in system-level components, as highlighted by ATT&CK framework techniques related to privilege escalation through registry manipulation. Organizations should implement additional monitoring for unusual registry modifications and privilege escalation events, particularly in environments where application compatibility features are actively used. The security update process should include thorough testing to ensure compatibility with existing application compatibility settings while addressing the underlying vulnerability. This case study emphasizes the need for continuous security assessment of system components that interface with critical system resources like the Windows registry.