CVE-2024-21302 in Windows
Summary
by MITRE • 08/08/2024
Summary: Microsoft was notified that an elevation of privilege vulnerability exists in Windows based systems supporting Virtualization Based Security (VBS) including a subset of Azure Virtual Machine SKUS; enabling an attacker with administrator privileges to replace current versions of Windows system files with outdated versions. By exploiting this vulnerability, an attacker could reintroduce previously mitigated vulnerabilities, circumvent some features of VBS, and exfiltrate data protected by VBS. For more information on Windows versions and VM SKUs supporting VBS, reference: Virtualization-based Security (VBS) | Microsoft Learn.. Microsoft is developing a security update to mitigate this vulnerability, but it is not yet available. Guidance to help customers reduce the risks associated with this vulnerability and to protect their systems until the mitigation is available in a Windows security update is provided in the Recommended Actions section of this CVE. This CVE will be updated when the mitigation is available in a Windows security update. We highly encourage customers to subscribe to Security Update Guide notifications to receive an alert when this update occurs. Details: A security researcher informed Microsoft of an elevation of privilege vulnerability in Windows 10, Windows 11, Windows Server 2016, Windows Server 2019, Windows Server 2022 , and a subset of Azure Virtual Machines (VM) SKUs with a Windows based guestOS supporting VBS. The vulnerability enables an attacker with administrator privileges on the target system to replace current Windows system files with outdated versions. Successful exploitation provides an attacker with the ability to reintroduce previously mitigated vulnerabilities, circumvent VBS security features, and exfiltrate data protected by VBS. Microsoft is developing a security update that will revoke outdated, unpatched VBS system files to mitigate this vulnerability, but it is not yet available. Due to the complexity of blocking such a large quantity of files, rigorous testing is required to avoid integration failures or regressions. This CVE will be updated with new information and links to the security updates once available. We highly encourage customers subscribe to Security Update Guide notifications to be alerted of updates. See Microsoft Technical Security Notifications and Security Update Guide Notification System News: Create your profile now – Microsoft Security Response Center. Microsoft is not aware of any attempts to exploit this vulnerability. However, a public presentation regarding this vulnerability was hosted at BlackHat on August 07th, 2024. The presentation was appropriately coordinated with Microsoft but may change the threat landscape. Customers concerned with these risks should reference the guidance provided in the Recommended Actions section of this CVE to protect their systems. Recommended Actions: The following recommendations do not mitigate the vulnerability but can be used to reduce the risk of exploitation until the security update is available.
Configure “Audit Object Access” settings to monitor attempts to access files, such as handle creation, read / write operations, or modifications to security descriptors.
Audit File System - Windows 10 | Microsoft Learn Apply a basic audit policy on a file or folder - Windows 10 | Microsoft Learn
Auditing sensitive privileges used to identify access, modification, or replacement of VBS related files could help indicacte attempts to exploit this vulnerability.
Audit Sensitive Privilege Use - Windows 10 | Microsoft Learn
Protect your Azure tenant by investigating administrators and users flagged for risky sign-ins and rotating their credentials.
Investigate risk Microsoft Entra ID Protection - Microsoft Entra ID Protection | Microsoft Learn
Enabling Multi-Factor Authentication can also help alleviate concerns about compromised accounts or exposure.
Enforce multifactor...
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Analysis
by VulDB Data Team • 02/05/2026
This elevation of privilege vulnerability affects Windows systems that support Virtualization Based Security including specific Azure Virtual Machine SKUs and represents a critical weakness in the operating system's file integrity mechanisms. The flaw allows an attacker with administrator privileges to substitute current Windows system files with older, unpatched versions, effectively creating a backdoor that can reintroduce previously addressed security issues. This vulnerability directly undermines the security assurances provided by VBS by enabling attackers to bypass protection mechanisms and access data that should remain encrypted or restricted. The technical nature of this flaw falls under CWE-276, which describes improper privilege management, and specifically targets the integrity controls that VBS is designed to enforce. The vulnerability impacts multiple Windows versions including Windows 10, Windows 11, Windows Server 2016, Windows Server 2019, and Windows Server 2022, making it particularly widespread across the enterprise landscape.
The operational implications of this vulnerability are severe as it enables attackers to circumvent security controls that are fundamental to modern Windows security architectures. When exploited, the vulnerability allows for the reintroduction of previously mitigated vulnerabilities, essentially creating a time machine for security flaws that have already been addressed. This capability undermines the security posture of affected systems and enables data exfiltration from VBS-protected data stores. The vulnerability operates through a file replacement mechanism that targets the core system files, making it particularly dangerous because it can disable security features that have been specifically implemented to protect against such attacks. From an attacker's perspective, this represents a sophisticated method of maintaining persistence while avoiding detection, as the replaced files may appear legitimate to security monitoring systems.
The attack vector requires an attacker to already possess administrator privileges on the target system, which makes this vulnerability more challenging to exploit but also more dangerous when successful. The attacker can leverage this access to modify critical system files, effectively rolling back security updates and creating a persistent backdoor. This vulnerability aligns with ATT&CK technique T1548.001, which describes abuse of elevation of privilege through file system manipulation, and T1070.006, which covers file deletion or modification. The complexity of the attack surface is compounded by the fact that it affects Azure Virtual Machines, creating additional exposure for cloud environments where VBS is commonly implemented. Microsoft's recommended actions focus on monitoring and auditing rather than direct mitigation, indicating that the vulnerability's nature makes it difficult to patch without risking system instability or regression issues.
Microsoft's response involves developing a security update that will revoke outdated VBS system files, but this requires extensive testing due to the large number of files that might be affected. The delay in availability creates a window of vulnerability that organizations must address through proactive monitoring and access control measures. The fact that this vulnerability was publicly presented at BlackHat 2024 suggests that threat actors may be developing exploitation techniques, even though Microsoft has not reported active exploitation attempts. Organizations should implement comprehensive audit policies to monitor access to VBS-related files and sensitive privileges, as these activities can serve as early indicators of exploitation attempts. The recommended actions emphasize the importance of protecting Azure environments through credential rotation and multi-factor authentication, which helps mitigate the risk of account compromise that could lead to exploitation. These measures align with the principle of least privilege and defense in depth, providing multiple layers of protection while awaiting the official security update that will address the root cause of the vulnerability.