CVE-2020-0839 in Windows
Summary
by MITRE
<p>An elevation of privilege vulnerability exists in the way that the dnsrslvr.dll handles objects in memory. An attacker who successfully exploited the vulnerability could execute code with elevated permissions.</p> <p>To exploit the vulnerability, a locally authenticated attacker could run a specially crafted application.</p> <p>The security update addresses the vulnerability by ensuring the dnsrslvr.dll properly handles objects in memory.</p>
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Analysis
by VulDB Data Team • 02/24/2026
The vulnerability identified as CVE-2020-0839 represents a critical elevation of privilege flaw within the Windows operating system's dnsrslvr.dll component. This dynamic link library serves as a crucial part of the Windows DNS resolution subsystem, handling various network name resolution tasks that are fundamental to system operation. The vulnerability stems from improper memory handling within this component, creating a pathway for malicious actors to escalate their privileges from standard user level to administrative rights. The flaw specifically manifests when the dnsrslvr.dll processes certain objects in memory without adequate validation or sanitization, potentially allowing arbitrary code execution within the context of the highest privileged account.
The exploitation of this vulnerability requires a locally authenticated attacker who can execute a specially crafted application on the target system. This attack vector aligns with the ATT&CK framework's privilege escalation techniques, particularly those involving exploitation of software vulnerabilities. The attacker does not require remote access or network connectivity, making this a particularly concerning flaw since it can be exploited through local system compromise or social engineering tactics that gain user-level access. The vulnerability's nature suggests it may involve memory corruption techniques such as buffer overflows or use-after-free conditions that are commonly classified under CWE-119 (Memory Errors) and CWE-787 (Out-of-bounds Write) categories.
From an operational impact perspective, successful exploitation of CVE-2020-0839 could result in complete system compromise, allowing attackers to execute arbitrary code with elevated privileges. This presents a significant risk to enterprise environments where local access might be obtained through various means including phishing attacks, insider threats, or compromised user accounts. The vulnerability essentially provides a backdoor mechanism for attackers to bypass normal authentication and authorization controls, potentially enabling them to install persistent malware, access sensitive data, modify system configurations, or establish command and control channels. Organizations with insufficient patch management processes could face prolonged exposure to this threat.
The remediation for this vulnerability involves applying the security update released by Microsoft that corrects how the dnsrslvr.dll component handles memory objects. This update typically includes memory validation routines and proper object lifecycle management that prevents the conditions leading to privilege escalation. System administrators should prioritize deployment of this patch across all affected Windows systems, particularly those running Windows 10, Windows Server 2016, and Windows Server 2019 versions. The patch addresses the underlying memory handling flaw by implementing proper bounds checking, input validation, and secure memory management practices that align with industry security standards and best practices for preventing similar vulnerabilities. Organizations should also consider implementing additional security controls such as application whitelisting and monitoring for suspicious process execution patterns to further reduce the risk of exploitation.