CVE-2020-0840 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-2020-0841, CVE-2020-0849, CVE-2020-0896.
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Analysis
by VulDB Data Team • 04/10/2024
The vulnerability described in CVE-2020-0840 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 provides complete control over the affected system. The issue stems from the Windows kernel's insufficient validation mechanisms when processing hard link operations, creating a pathway for malicious actors to manipulate file system permissions and gain unauthorized administrative access.
From a technical perspective, the flaw manifests in the Windows file system's handling of hard links, which are multiple directory entries that point to the same file data on disk. When Windows processes hard link creation or manipulation operations, it fails to properly validate the security context and access permissions associated with these operations. This improper validation creates a race condition or access control bypass that can be exploited by attackers to manipulate file permissions and gain elevated privileges. The vulnerability is particularly dangerous because it operates at the kernel level, making it extremely difficult to detect and mitigate without proper system hardening measures.
The operational impact of this vulnerability extends far beyond simple privilege escalation, as it provides attackers with complete system compromise capabilities. Once an attacker successfully exploits this vulnerability, they can execute arbitrary code with SYSTEM privileges, access all system files and data, modify system configurations, install malware, and establish persistent backdoors. This makes the vulnerability particularly attractive to advanced persistent threat groups and cybercriminal organizations seeking to establish long-term access to targeted systems. The vulnerability affects multiple Windows versions including Windows 10, Windows Server 2016, and Windows Server 2019, making it a widespread concern across enterprise environments.
Security professionals should note that this vulnerability aligns with CWE-264, which describes permissions, privileges, and access control weaknesses in software systems. The flaw represents a classic case of insufficient access control validation, where the system fails to properly enforce security boundaries when processing hard link operations. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques under the T1068 category, specifically targeting kernel-level privilege escalation methods. Organizations should implement immediate mitigations including applying Microsoft security patches, disabling unnecessary hard link creation capabilities, and monitoring for suspicious file system operations that could indicate exploitation attempts.
Mitigation strategies should focus on both immediate patching and operational security measures to protect against exploitation of this vulnerability. Microsoft released security updates that address the hard link handling issue by strengthening the validation mechanisms within the Windows kernel. System administrators should prioritize deployment of these patches across all affected systems while implementing additional monitoring controls to detect anomalous hard link creation activities. Network segmentation and principle of least privilege configurations can help limit the potential impact if exploitation occurs, though the vulnerability's kernel-level nature makes complete protection challenging without proper patch management. Regular security assessments and vulnerability scanning should specifically target this class of vulnerabilities to identify systems that may not have received timely updates, as delayed patching can leave organizations vulnerable to exploitation by threat actors who may have already developed working exploits for this vulnerability.