CVE-2019-1235 in Windows
Summary
by MITRE
An elevation of privilege vulnerability exists in Windows Text Service Framework (TSF) when the TSF server process does not validate the source of input or commands it receives, aka 'Windows Text Service Framework Elevation of Privilege Vulnerability'.
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Analysis
by VulDB Data Team • 08/19/2020
The Windows Text Service Framework represents a critical component within the Windows operating system that manages text input services and facilitates communication between applications and text services. This framework enables various text processing functionalities including input method editors, speech recognition systems, and other text-related services that enhance user interaction with the operating system. The vulnerability identified as CVE-2019-1235 stems from insufficient validation mechanisms within the TSF server process, creating a pathway for malicious actors to exploit the framework's trust model. The flaw specifically manifests when the TSF server process fails to properly authenticate or validate the origin of input data and commands it processes, allowing unauthorized entities to inject malicious code or commands into the system.
This elevation of privilege vulnerability operates through a fundamental flaw in the TSF server's security architecture where it assumes all incoming input originates from trusted sources without proper verification. The vulnerability falls under the Common Weakness Enumeration category CWE-20, which describes "Improper Input Validation" as the underlying weakness that enables this privilege escalation. Attackers can leverage this weakness by crafting malicious input that appears to come from legitimate text services, thereby bypassing the normal security boundaries that should protect the system from unauthorized code execution. The TSF framework's design assumes that processes within the same security context can be trusted, creating an attack surface where malicious code can escalate privileges to SYSTEM level access.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with the ability to execute arbitrary code with the highest system privileges. This allows for complete system compromise, enabling attackers to install malware, modify system files, access sensitive data, and establish persistent backdoors within the affected systems. The vulnerability affects multiple Windows versions including Windows 10, Windows Server 2016, and Windows Server 2019, making it particularly dangerous given the widespread deployment of these operating systems across enterprise environments. Security researchers have documented that this vulnerability can be exploited through various attack vectors including malicious input method editors, compromised text services, or through exploitation of other vulnerabilities that can be chained with this privilege escalation flaw.
Mitigation strategies for CVE-2019-1235 should focus on implementing proper input validation and source authentication mechanisms within the TSF framework. Microsoft released security updates that address this vulnerability by strengthening the validation processes within the TSF server component and implementing more rigorous authentication checks for incoming commands. Organizations should ensure immediate deployment of the relevant security patches and consider implementing additional security controls such as application whitelisting to prevent unauthorized text services from executing. The vulnerability demonstrates the importance of following the principle of least privilege and proper input validation as outlined in the MITRE ATT&CK framework under the privilege escalation techniques. System administrators should also monitor for suspicious text service activity and implement network segmentation to limit the potential impact of successful exploitation attempts. Given the nature of this vulnerability, regular security assessments of text input services and proper access controls should be maintained to prevent unauthorized modification of text service configurations that could lead to similar privilege escalation scenarios.