CVE-2019-1090 in Windows
Summary
by MITRE
An elevation of privilege vulnerability exists in the way that the dnsrslvr.dll handles objects in memory, aka 'Windows dnsrlvr.dll Elevation of Privilege Vulnerability'.
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Analysis
by VulDB Data Team • 07/02/2020
The vulnerability identified as CVE-2019-1090 represents a critical elevation of privilege flaw within the Windows dnsrslvr.dll component, which is part of the Windows operating system's DNS resolution functionality. This vulnerability specifically manifests in how the dnsrslvr.dll manages memory objects, creating a potential pathway for malicious actors to escalate their privileges from standard user level to system-level access. The issue stems from improper handling of memory structures within the DNS resolver library, which is responsible for translating domain names into IP addresses across Windows systems. Security researchers have classified this as a privilege escalation vulnerability due to the potential for unauthorized code execution with elevated privileges, making it particularly dangerous in enterprise environments where multiple users interact with network resources.
The technical exploitation of this vulnerability occurs through memory corruption techniques that leverage weaknesses in the dnsrslvr.dll's object handling mechanisms. When the DNS resolver processes certain malformed or specially crafted input data, it fails to properly validate memory objects, potentially leading to buffer overflows or memory corruption conditions. This flaw allows attackers to manipulate memory contents in ways that can be leveraged to execute arbitrary code with system-level privileges. The vulnerability is particularly concerning because it operates within the core Windows networking stack, making it accessible through various attack vectors including network-based exploitation, malicious email attachments, or compromised websites that trigger DNS resolution. The underlying flaw aligns with CWE-121, which describes heap-based buffer overflow conditions, and CWE-125, which covers out-of-bounds read vulnerabilities, both of which are commonly exploited in privilege escalation scenarios.
From an operational perspective, this vulnerability presents significant risk to Windows environments since dnsrslvr.dll is integral to normal DNS resolution operations across all supported Windows versions including Windows 7, Windows 8.1, Windows 10, and Windows Server 2008, 2012, 2012 R2, 2016, and 2019. Attackers can exploit this vulnerability without requiring special privileges, making it particularly dangerous as it can be leveraged by malicious actors to gain unauthorized system access. The impact extends beyond individual system compromise to potential network-wide infiltration, especially in environments where DNS servers are centrally managed and accessed by multiple users. Organizations may experience unauthorized data access, system takeover, or deployment of persistent backdoors through exploitation of this vulnerability. The ATT&CK framework categorizes this as a privilege escalation technique, specifically falling under the 'Exploitation for Privilege Escalation' tactic where adversaries leverage software vulnerabilities to gain elevated system access.
Mitigation strategies for CVE-2019-1090 primarily involve applying Microsoft security patches and updates as released through the Windows Update mechanism or Microsoft Security Response Center. Organizations should prioritize immediate deployment of the relevant security updates, as Microsoft has classified this vulnerability with a critical severity rating. Additionally, implementing network segmentation and access controls can reduce the attack surface by limiting potential exploitation vectors. Security monitoring should include detection of unusual DNS resolution patterns that might indicate exploitation attempts, while endpoint protection solutions should be configured to monitor for suspicious memory operations or process injection techniques. Network administrators should also consider disabling unnecessary DNS resolution capabilities where possible, particularly in environments where DNS queries are not essential for core operations. The vulnerability demonstrates the importance of maintaining up-to-date security patches and implementing defense-in-depth strategies to protect against zero-day exploitation attempts. Organizations should also conduct regular security assessments to identify potential exploitation opportunities and ensure that all Windows systems remain protected against known vulnerabilities.