CVE-2019-0733 in Windows
Summary
by MITRE
A security feature bypass vulnerability exists in Windows Defender Application Control (WDAC) which could allow an attacker to bypass WDAC enforcement, aka 'Windows Defender Application Control Security Feature Bypass Vulnerability'.
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Analysis
by VulDB Data Team • 06/09/2020
The vulnerability identified as CVE-2019-0733 represents a critical security feature bypass in Windows Defender Application Control, a core component of Microsoft's endpoint protection framework designed to prevent unauthorized code execution. This flaw resides within the WDAC implementation that enforces application control policies to restrict which applications can run on Windows systems. The vulnerability specifically affects the enforcement mechanism that should prevent execution of unsigned or unauthorized applications, creating a pathway for malicious actors to circumvent these protective measures. The issue stems from improper validation of code integrity checks that should occur during the application execution process, allowing attackers to bypass the policy enforcement controls that are meant to be the first line of defense against malicious software.
The technical nature of this vulnerability can be categorized under CWE-284, which addresses improper access control, and more specifically relates to improper enforcement of policies within security systems. The flaw manifests when WDAC fails to properly validate the integrity of code signatures or when it incorrectly evaluates the trust status of applications that should be blocked by policy enforcement. Attackers can exploit this weakness by crafting malicious code that appears to meet the requirements for execution within the controlled environment, effectively bypassing the security controls that should prevent such execution. This bypass occurs at the kernel level where WDAC enforces its policies, making it particularly dangerous as it operates below the normal user-space protections and can potentially allow for privilege escalation or further system compromise.
The operational impact of CVE-2019-0733 extends beyond simple policy bypass, as it creates a persistent threat vector that can be exploited across various attack scenarios. The vulnerability enables attackers to execute malicious code without triggering WDAC alerts or enforcement mechanisms, effectively rendering the application control policies ineffective. This weakness can be leveraged as part of broader attack chains where initial compromise occurs through other vectors, but the attacker then uses this bypass to maintain persistence or escalate privileges. The attack surface includes scenarios where attackers might attempt to execute malicious PowerShell scripts, install backdoors, or deploy additional malware components that would normally be blocked by WDAC policies. The vulnerability is particularly concerning in enterprise environments where WDAC is used to enforce strict application control policies and prevent unauthorized software execution.
Mitigation strategies for CVE-2019-0733 should focus on immediate patch deployment through Microsoft's security updates, as the vendor has released patches addressing this specific vulnerability in their Windows updates. Organizations should also implement additional defensive measures including enhanced monitoring for suspicious execution patterns, regular review of WDAC policies, and implementation of layered security controls that do not rely solely on application control. The mitigation approach aligns with ATT&CK framework techniques related to privilege escalation and persistence, suggesting that organizations should monitor for unusual execution behavior that might indicate exploitation attempts. Network segmentation and endpoint detection and response solutions should be deployed to provide additional visibility into potential exploitation attempts. System administrators should also consider temporarily disabling WDAC enforcement during critical maintenance windows while patches are applied, though this should be done with careful consideration of the increased risk exposure during the patching process.