CVE-2011-1967 in Windows
Summary
by MITRE
Winsrv.dll in the Client/Server Run-time Subsystem (aka CSRSS) in the Win32 subsystem in Microsoft Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista SP2, Windows Server 2008 SP2, R2, and R2 SP1, and Windows 7 Gold and SP1 does not properly check permissions for sending inter-process device-event messages from low-integrity processes to high-integrity processes, which allows local users to gain privileges via a crafted application, aka "CSRSS Vulnerability."
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Analysis
by VulDB Data Team • 01/12/2025
The CVE-2011-1967 vulnerability resides within the Client/Server Run-time Subsystem (CSRSS) component of Microsoft Windows operating systems, specifically affecting Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista SP2, Windows Server 2008 SP2 and R2, and Windows 7 Gold and SP1. This flaw represents a critical privilege escalation vulnerability that exploits improper permission checking mechanisms within the Win32 subsystem, allowing malicious applications to manipulate inter-process communication channels between processes of different integrity levels. The vulnerability specifically targets the Winsrv.dll library which handles device-event messages within the CSRSS process, creating a pathway for low-integrity processes to communicate with high-integrity processes without proper authorization checks.
The technical flaw manifests through a lack of proper integrity level validation when processing device-event messages sent between processes in the Windows operating system. When a low-integrity process attempts to send a device-event message to a high-integrity process, the CSRSS component fails to verify that the sending process has appropriate permissions to perform such operations. This permission bypass occurs because the system does not properly enforce the mandatory integrity control mechanisms that should prevent lower-privilege processes from directly influencing higher-privilege system components. The vulnerability stems from the improper implementation of access control checks within the CSRSS subsystem, which is responsible for managing critical system processes and maintaining the security boundaries between different integrity levels.
Operationally, this vulnerability enables local attackers to escalate their privileges from standard user level to system-level access by crafting malicious applications that exploit the improper permission checking. An attacker can create a low-integrity process that sends specially crafted device-event messages to high-integrity processes, potentially gaining access to system resources, modifying critical system files, or executing arbitrary code with elevated privileges. The impact extends beyond simple privilege escalation as it can lead to complete system compromise, allowing attackers to establish persistent backdoors, extract sensitive data, or disable security controls. This vulnerability particularly affects enterprise environments where users may have standard account privileges but could leverage this flaw to gain unauthorized access to critical systems and data.
The vulnerability maps to CWE-284, which describes improper access control in software systems, and aligns with several ATT&CK tactics including privilege escalation through process injection and credential access. Organizations should implement immediate mitigations including applying the relevant Microsoft security updates, implementing strict integrity level controls, and monitoring for suspicious process communication patterns. System administrators should also consider implementing additional security measures such as mandatory integrity control enforcement, process monitoring tools, and regular security audits to detect potential exploitation attempts. The recommended remediation involves deploying the Microsoft security bulletin updates that address the CSRSS permission checking flaws, while also implementing defense-in-depth strategies to minimize the impact if exploitation occurs.