CVE-2020-0849 in Windows
Summary
by MITRE
An elevation of privilege vulnerability exists when Windows improperly handles hard links, aka 'Windows Hard Link Elevation of Privilege Vulnerability'. This CVE ID is unique from CVE-2020-0840, CVE-2020-0841, CVE-2020-0896.
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Analysis
by VulDB Data Team • 04/11/2024
The vulnerability identified as CVE-2020-0849 represents a critical elevation of privilege flaw within the Windows operating system that specifically exploits improper handling of hard links. This issue allows authenticated attackers with standard user privileges to escalate their access rights and potentially gain system-level control. The vulnerability stems from Windows' inadequate validation and processing of hard link operations, creating a pathway for malicious actors to bypass security controls that should normally prevent privilege escalation.
The technical root cause of this vulnerability lies in how Windows manages file system hard links, which are multiple directory entries pointing to the same file data on disk. When Windows processes hard link operations, it fails to properly validate the security context and access permissions associated with these links. This flaw enables attackers to create malicious hard link structures that can be exploited to access files and resources that should normally be restricted to higher privilege users. The vulnerability specifically manifests when the operating system does not adequately enforce access control lists and security descriptors during hard link creation and manipulation processes.
From an operational impact perspective, this vulnerability poses significant risks to enterprise environments where multiple users share systems and where standard user accounts are commonly used. Attackers can leverage this flaw to access sensitive system files, modify critical registry entries, and potentially install malicious software with elevated privileges. The vulnerability affects various Windows versions including Windows 10, Windows Server 2016, and Windows Server 2019, making it a widespread concern across corporate networks. Security researchers have noted that this vulnerability can be particularly dangerous when combined with other exploitation techniques, as it provides a reliable method for privilege escalation that bypasses traditional security mechanisms.
The exploitation of CVE-2020-0849 aligns with several tactics outlined in the MITRE ATT&CK framework, particularly those related to privilege escalation and persistence. The vulnerability enables techniques such as "Exploitation for Privilege Escalation" and "File and Directory Permissions Modification" by allowing attackers to manipulate file access controls through hard link manipulation. This flaw also connects to CWE-264, which addresses permissions, privileges, and access control issues in software design. Organizations should consider implementing comprehensive monitoring solutions that can detect unusual hard link creation patterns and file access anomalies that may indicate exploitation attempts. The vulnerability's impact is further amplified by its ability to bypass standard security controls, making traditional defense-in-depth strategies less effective against this specific threat vector.
Mitigation strategies for CVE-2020-0849 should include immediate deployment of Microsoft security patches, which address the underlying hard link handling mechanisms. System administrators should also implement enhanced monitoring of file system activities, particularly focusing on hard link creation and modification events. Additional protective measures include restricting user privileges where possible, implementing strict access control policies, and conducting regular security audits of file system permissions. Organizations should also consider network segmentation and application whitelisting to limit the potential impact of successful exploitation attempts. The vulnerability's classification as a privilege escalation flaw makes it particularly important to maintain robust incident response procedures that can quickly detect and contain exploitation attempts.