CVE-2020-0841 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-2020-0849, CVE-2020-0896.
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Analysis
by VulDB Data Team • 04/10/2024
The vulnerability described in CVE-2020-0841 represents a critical elevation of privilege flaw within the Windows operating system that specifically exploits improper handling of hard links. This vulnerability allows attackers to escalate their privileges from a standard user account to SYSTEM level access, which constitutes a severe security risk for enterprise environments. The issue stems from how Windows manages file system hard links, which are multiple directory entries that point to the same file on disk, creating a situation where access controls can be bypassed through malicious manipulation of these link structures.
The technical root cause of this vulnerability lies in the Windows kernel's insufficient validation of hard link operations, particularly when processing file system requests that involve symbolic or hard links. When a malicious user creates or manipulates hard links in specific ways, the system fails to properly enforce access control lists and file permissions, allowing unauthorized access to restricted resources. This flaw operates at the kernel level and affects the core file system functionality, making it particularly dangerous because it can be exploited to gain complete administrative control over affected systems. The vulnerability specifically manifests when Windows processes hard link creation or modification operations without adequate verification of the user's permissions or the integrity of the link structure.
From an operational impact perspective, this vulnerability enables attackers to perform privilege escalation attacks that can result in complete system compromise. An attacker with limited user access can leverage this flaw to execute arbitrary code with SYSTEM privileges, potentially leading to data exfiltration, persistence mechanisms installation, or further network reconnaissance. The vulnerability affects multiple Windows versions including Windows 10, Windows Server 2016, and Windows Server 2019, making it a widespread concern for organizations. This type of vulnerability aligns with CWE-264, which addresses permissions, privileges, and access controls, and represents a classic example of how file system implementation flaws can create security boundaries that can be systematically exploited.
The exploitation of this vulnerability typically involves creating malicious hard links that bypass normal access controls, potentially allowing attackers to read or modify protected system files and registry entries. Security researchers have identified that the vulnerability can be triggered through various attack vectors including file system manipulation, application-specific file operations, and potentially through malicious software installation that leverages the hard link functionality. Organizations should consider this vulnerability in their threat modeling and incident response planning, as it represents a sophisticated attack vector that can be used to establish persistent access to compromised systems. Mitigation strategies include applying Microsoft security patches immediately, implementing strict file system access controls, monitoring for unusual hard link creation patterns, and conducting regular security assessments to identify potential exploitation attempts.
This vulnerability demonstrates the importance of proper kernel-level security implementation and the critical need for thorough testing of file system operations, particularly those involving link structures. The flaw represents a failure in the principle of least privilege enforcement and highlights the complexity of maintaining secure file system operations in modern operating systems. Organizations should also consider implementing additional security controls such as application whitelisting, enhanced monitoring of file system changes, and regular security updates to prevent exploitation of similar vulnerabilities. The vulnerability's classification within the ATT&CK framework would likely fall under privilege escalation techniques, specifically targeting the use of operating system features to gain higher-level access rights.