CVE-2009-1127 in Windows
Summary
by MITRE
win32k.sys in the kernel in Microsoft Windows 2000 SP4, XP SP2 and SP3, Server 2003 SP2, Vista Gold, SP1, and SP2, and Server 2008 Gold and SP2 does not correctly validate an argument to an unspecified system call, which allows local users to gain privileges via a crafted application that triggers a NULL pointer dereference, aka "Win32k NULL Pointer Dereferencing Vulnerability."
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Analysis
by VulDB Data Team • 03/17/2021
The CVE-2009-1127 vulnerability represents a critical privilege escalation flaw within the Windows kernel mode driver win32k.sys that affects multiple versions of Microsoft Windows operating systems. This vulnerability resides in the kernel-level subsystem responsible for handling graphical user interface components and system calls related to window management. The flaw manifests when the win32k.sys driver fails to properly validate input arguments during unspecified system calls, creating a condition where malicious applications can manipulate kernel execution flow through crafted inputs. The vulnerability specifically enables local attackers to achieve privilege escalation from standard user level to kernel level access, fundamentally compromising system security. This type of vulnerability is classified under CWE-125 as an out-of-bounds read condition, though the specific manifestation involves a NULL pointer dereference that can be exploited by local users.
The technical exploitation of this vulnerability occurs through a carefully crafted application that triggers a system call with malformed arguments, causing the win32k.sys driver to attempt to dereference a NULL pointer. When the kernel processes this invalid input, it results in an unexpected system state where the execution flow can be manipulated to gain elevated privileges. The vulnerability requires local system access to exploit, meaning an attacker must already have a user account on the target system. However, the impact is severe as it allows full system compromise once successfully exploited. The null pointer dereference creates a condition where the kernel memory management system encounters an invalid memory reference, potentially leading to arbitrary code execution at kernel level. This behavior aligns with ATT&CK technique T1068 which covers local privilege escalation through kernel exploits, and represents a classic example of a kernel-mode privilege escalation vulnerability.
The operational impact of CVE-2009-1127 extends beyond simple privilege escalation as it provides attackers with complete control over affected systems. Once exploited, attackers can execute arbitrary code with kernel-level privileges, enabling them to bypass all user-mode security controls, modify system files, install rootkits, and access all system resources. The vulnerability affects a wide range of Windows versions including legacy systems like Windows 2000 and Windows Server 2003, making it particularly dangerous for organizations maintaining older infrastructure. This vulnerability also demonstrates the challenges of maintaining security in complex kernel-mode drivers where input validation is critical for preventing exploitation. The attack vector requires local access, but the privilege escalation capability makes it particularly attractive to attackers who have already compromised user accounts, as it provides a pathway to full system compromise. Organizations affected by this vulnerability must implement immediate mitigation strategies including applying security patches, disabling unnecessary services, and implementing monitoring for suspicious system calls.
Microsoft addressed this vulnerability through security updates that corrected the input validation logic in win32k.sys, requiring proper validation of system call arguments before processing. The patch ensures that invalid or malformed inputs are properly rejected rather than allowing the kernel to process them and potentially crash or execute malicious code. Security professionals should note that this vulnerability highlights the importance of kernel-mode security and proper input validation in system drivers. The vulnerability serves as a reminder that even minor input validation flaws in kernel components can result in severe privilege escalation capabilities. Organizations should maintain comprehensive patch management programs and regularly audit their systems for unpatched vulnerabilities. The exploitability of this vulnerability underscores the need for layered security approaches including user access controls, system monitoring, and regular security assessments. This vulnerability also demonstrates the importance of maintaining up-to-date security patches, particularly for legacy systems that may not receive extended support but remain in production environments.