CVE-2020-0835 in Defender Antimalware Platform
Summary
by MITRE
An elevation of privilege vulnerability exists when Windows Defender antimalware platform improperly handles hard links, aka 'Windows Defender Antimalware Platform Hard Link Elevation of Privilege Vulnerability'.
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Analysis
by VulDB Data Team • 10/09/2020
The vulnerability identified as CVE-2020-0835 represents a critical elevation of privilege flaw within the Windows Defender antimalware platform that stems from improper handling of hard links. This weakness allows malicious actors to escalate their privileges from standard user level to system level by exploiting the way Windows Defender processes hard link structures during file operations. The vulnerability specifically affects the antimalware platform's interaction with hard links, creating a pathway for unauthorized code execution and privilege escalation that bypasses normal security boundaries. Microsoft classified this issue as a high-severity vulnerability due to its potential to enable complete system compromise when exploited by attackers.
The technical root cause of CVE-2020-0835 lies in the Windows Defender antimalware platform's inadequate validation and handling of hard link file operations. When Windows Defender processes files that contain hard links, it fails to properly verify the legitimacy of these link structures, allowing an attacker to manipulate the system's file handling mechanisms. The flaw occurs during the scanning and processing phase where hard links are not appropriately sanitized or validated before being processed by the antimalware engine. This improper handling creates a condition where malicious hard links can be used to circumvent security checks and execute code with elevated privileges. The vulnerability is categorized under CWE-264 due to improper privileges management and falls under the ATT&CK technique T1068 which describes exploiting privileges through legitimate system tools.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with a persistent means of gaining system-level access that can be leveraged for further compromise. Once successfully exploited, the attacker can execute arbitrary code with system privileges, potentially leading to complete system takeover, data exfiltration, or deployment of additional malware. The vulnerability affects multiple Windows versions including Windows 10, Windows Server 2016, and Windows Server 2019, making it particularly dangerous in enterprise environments where these systems are commonly deployed. The attack vector typically involves creating malicious hard links in specific locations where Windows Defender scans files, then triggering the antimalware platform to process these links, thereby executing the malicious payload with elevated privileges. This vulnerability is particularly concerning because it leverages legitimate antimalware functionality to achieve its malicious goals, making detection more challenging.
Mitigation strategies for CVE-2020-0835 primarily focus on applying Microsoft's security patches and updates as soon as they become available. Organizations should prioritize immediate deployment of the relevant Windows updates that address this vulnerability in the Windows Defender platform. System administrators should also consider implementing additional security controls such as restricting hard link creation capabilities in sensitive directories and monitoring for unusual hard link creation patterns. The vulnerability can be mitigated through proper system hardening practices including disabling unnecessary antimalware scanning of user directories, implementing strict file permission controls, and maintaining regular security assessments. Additionally, security teams should monitor for exploitation attempts through anomalous file system activity and hard link creation patterns that may indicate attempted exploitation of this vulnerability. Organizations should also consider implementing network monitoring solutions to detect potential exploitation attempts and maintain detailed audit logs for forensic analysis. The remediation process should include comprehensive testing of patches in controlled environments before deployment to ensure compatibility with existing systems and applications.