CVE-2021-28440 in Windows
Summary
by MITRE • 04/14/2021
Windows Installer Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-26415.
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Analysis
by VulDB Data Team • 04/16/2021
The Windows Installer Elevation of Privilege Vulnerability identified as CVE-2021-28440 represents a critical security flaw in Microsoft Windows operating systems that allows attackers to escalate their privileges from standard user level to administrative rights. This vulnerability specifically targets the Windows Installer service and its handling of certain installation packages, creating an opportunity for malicious actors to execute arbitrary code with elevated privileges. The flaw exists in the way Windows Installer processes and validates installation files, particularly when dealing with specially crafted msi packages that can bypass normal security restrictions. This vulnerability is distinct from CVE-2021-26415, which affects a different component of the Windows installation process, making it crucial for security professionals to understand the specific attack vectors and mitigation strategies for each vulnerability. The vulnerability falls under CWE-264, which addresses permissions, privileges, and access controls, specifically targeting the improper handling of installation privileges within the Windows operating system.
The technical implementation of this vulnerability involves a flaw in the Windows Installer service's validation mechanism when processing installation packages. Attackers can exploit this by creating malicious installation packages that manipulate the installer's execution flow, allowing them to bypass the normal privilege checking procedures. The vulnerability typically manifests when a user with standard privileges attempts to install a malicious package, but the installer service incorrectly grants administrative privileges during the installation process. This flaw is particularly dangerous because it can be triggered through various attack vectors including phishing emails, malicious websites, or compromised applications that attempt to install software. The exploitation requires minimal user interaction and can be automated, making it a significant threat to enterprise environments where users may inadvertently execute malicious installation packages. The vulnerability is classified under the ATT&CK framework as privilege escalation technique T1068, specifically targeting the Windows Installer service as a means to gain elevated system access.
The operational impact of CVE-2021-28440 is substantial across enterprise environments, as it can enable attackers to establish persistent access to systems and potentially compromise entire networks. Once successfully exploited, attackers can install backdoors, modify system files, create new administrative accounts, or deploy additional malicious software without detection. The vulnerability affects multiple Windows versions including Windows 10, Windows Server 2016, and Windows Server 2019, making it a widespread threat across modern enterprise infrastructure. Organizations that rely heavily on software deployment processes or have users with standard privileges are particularly at risk, as the attack surface expands to include any legitimate installation activities that might be compromised. The vulnerability can also be leveraged as part of multi-stage attacks, where initial access is gained through other means and then the installer privilege escalation is used to establish persistence and expand control over the compromised system. Security teams must recognize that this vulnerability can be used to bypass traditional security controls, including application whitelisting mechanisms that might not restrict installer services.
Mitigation strategies for CVE-2021-28440 should focus on immediate patch deployment combined with enhanced monitoring of installation activities. Microsoft released security updates that address the vulnerability by correcting the installer service's privilege validation logic and implementing additional checks during package processing. Organizations should prioritize patch management and ensure all systems are updated promptly to prevent exploitation. Additional defensive measures include implementing strict application control policies that limit which installation packages can be executed, monitoring for unusual installation activities, and configuring Windows Installer service restrictions to prevent unauthorized privilege escalation. Network segmentation and least privilege access controls can help limit the potential damage if exploitation occurs. Security monitoring should focus on detecting anomalous installation patterns, particularly those involving unsigned packages or packages from untrusted sources. The vulnerability also highlights the importance of user education and awareness programs to prevent accidental exploitation through social engineering attacks that trick users into executing malicious installation packages. Regular security assessments should include testing for the presence of this vulnerability and verification of implemented mitigations to ensure comprehensive protection against this specific privilege escalation threat.