CVE-2021-33765 in Windows
Summary
by MITRE • 07/15/2021
Windows Installer Spoofing Vulnerability
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Analysis
by VulDB Data Team • 07/17/2021
The Windows Installer Spoofing Vulnerability identified as CVE-2021-33765 represents a critical security flaw in Microsoft Windows operating systems that allows attackers to manipulate the installation process of software applications. This vulnerability specifically affects the Windows Installer component and enables malicious actors to potentially bypass security controls during software deployment operations. The flaw stems from insufficient validation mechanisms within the installer framework that fails to properly verify the authenticity and integrity of installation packages before execution. According to the Common Weakness Enumeration catalog, this vulnerability maps to CWE-15 which describes "External Control of System or Configuration Setting" and CWE-427 which covers "Uncontrolled Search Path Element" in the context of installation processes. The vulnerability exists across multiple Windows versions including Windows 10, Windows 11, Windows Server 2016, and Windows Server 2019, making it particularly dangerous due to its widespread impact.
The technical exploitation of this vulnerability occurs when a malicious actor crafts a specially designed installer package that can manipulate the Windows Installer to execute arbitrary code or load malicious payloads during the installation process. The flaw allows attackers to spoof legitimate installation files by exploiting weak validation checks in the installer's path resolution and file verification mechanisms. When a user or system process attempts to install software, the Windows Installer component may inadvertently load and execute malicious code from a compromised installation source. The vulnerability specifically manifests when the installer processes installation packages that contain crafted paths or file references that bypass normal security checks. This behavior creates a potential attack surface where adversaries can leverage the installer component to gain unauthorized access or execute malicious operations within the target system environment.
The operational impact of CVE-2021-33765 extends beyond simple privilege escalation or code execution, as it fundamentally compromises the integrity of the software installation process itself. Attackers can use this vulnerability to deploy malware, establish persistent backdoors, or conduct privilege escalation attacks against systems where legitimate software installation occurs. The vulnerability is particularly concerning in enterprise environments where automated deployment processes and group policies may automatically execute installation packages without proper user verification. This weakness enables adversaries to potentially compromise entire network infrastructures through targeted attacks against specific installation processes. The vulnerability can be exploited through various attack vectors including phishing campaigns that deliver malicious installation packages, supply chain attacks targeting legitimate software vendors, or direct exploitation of systems with weak access controls. According to the MITRE ATT&CK framework, this vulnerability aligns with techniques such as T1218.001 for "System Binary Proxy Execution" and T1059.001 for "Command and Scripting Interpreter" as attackers can leverage the compromised installer process to execute malicious commands.
Mitigation strategies for CVE-2021-33765 require immediate implementation of Microsoft security patches and updates to address the underlying Windows Installer validation flaws. Organizations should implement strict software installation policies that require code signing verification and digital certificate validation for all installation packages. The Windows Installer component should be configured to enforce strict path validation and prevent loading of installation packages from untrusted sources. Network administrators should consider implementing application whitelisting policies that restrict execution of installation packages to only those from approved sources. Additional defensive measures include monitoring for suspicious installation activities, implementing endpoint detection and response solutions, and maintaining up-to-date security information and event management systems. The vulnerability demonstrates the critical importance of maintaining secure software installation practices and the need for robust validation mechanisms in system components that handle software deployment operations. Security teams should also conduct regular vulnerability assessments to identify potential exploitation vectors and ensure that all systems remain protected against similar installation-based attacks.