CVE-2019-0795 in Windows
Summary
by MITRE
A remote code execution vulnerability exists when the Microsoft XML Core Services MSXML parser processes user input, aka 'MS XML Remote Code Execution Vulnerability'. This CVE ID is unique from CVE-2019-0790, CVE-2019-0791, CVE-2019-0792, CVE-2019-0793.
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Analysis
by VulDB Data Team • 07/11/2024
The vulnerability identified as CVE-2019-0795 represents a critical remote code execution flaw within Microsoft XML Core Services MSXML parser component. This vulnerability specifically manifests when the MSXML parser processes user-supplied input data, creating an avenue for malicious actors to execute arbitrary code on affected systems. The flaw resides in how the parser handles certain malformed XML input, particularly when processing external entity references and XML schema validation. The vulnerability affects multiple versions of Microsoft Windows operating systems including Windows 7, Windows 8.1, Windows Server 2008 R2, Windows Server 2012, Windows Server 2012 R2, and Windows Server 2016. The attack surface is broad as MSXML is extensively used across various Microsoft applications and services, making this vulnerability particularly dangerous for enterprise environments where XML processing is common.
The technical mechanism behind this vulnerability stems from improper input validation within the MSXML parser's handling of XML external entity declarations. When the parser encounters specially crafted XML documents containing malicious external entity references, it fails to properly sanitize the input before processing. This leads to a buffer overflow condition that can be exploited to execute arbitrary code with the privileges of the affected application. The vulnerability is categorized under CWE-121 as a buffer overflow condition, specifically manifesting as a stack-based buffer overflow when processing XML documents. The flaw enables attackers to leverage XML External Entity (XXE) attacks, where crafted XML input containing references to external resources can trigger unintended behavior in the parser. This vulnerability is particularly concerning because it can be triggered through various attack vectors including web applications, email attachments, and file processing scenarios that utilize MSXML for XML parsing operations.
The operational impact of CVE-2019-0795 extends beyond simple remote code execution, as it provides attackers with persistent access to compromised systems. Once exploited, attackers can establish command and control channels, escalate privileges, and move laterally within network environments. The vulnerability's exploitation does not require user interaction, making it particularly dangerous for automated attacks. Organizations using Microsoft Office applications, web servers processing XML content, and systems with MSXML installed are all at risk. The vulnerability's presence in widely deployed components means that successful exploitation can affect thousands of systems simultaneously, potentially leading to widespread data breaches and system compromise. Security researchers have identified that this vulnerability can be leveraged for privilege escalation attacks, where attackers can gain SYSTEM-level privileges on target systems, enabling them to execute any command and access all system resources.
Mitigation strategies for CVE-2019-0795 focus on both immediate patching and operational security measures. Microsoft released security updates through the Windows Update system, which should be deployed immediately across all affected systems. Organizations should also implement network segmentation and firewall rules to limit access to systems that process XML content from untrusted sources. The principle of least privilege should be enforced, ensuring that applications using MSXML run with minimal necessary permissions. Additionally, input validation should be strengthened at all levels where XML processing occurs, including web applications, email gateways, and file processing systems. Security teams should monitor network traffic for suspicious XML content and implement intrusion detection systems that can identify XXE attack patterns. The vulnerability aligns with several ATT&CK techniques including T1059 for command and scripting interpreter and T1068 for exploit for privilege escalation. Organizations should also consider implementing application whitelisting policies and disabling unnecessary XML processing capabilities where possible. Regular security assessments and penetration testing should be conducted to identify potential attack vectors that could leverage this vulnerability, ensuring comprehensive protection against both current and emerging threats.