CVE-2011-1873 in Windows
Summary
by MITRE
win32k.sys in the kernel-mode drivers in Microsoft Windows XP SP2, Windows Server 2003 SP2, Windows Vista SP1 and SP2, Windows Server 2008 Gold, SP2, R2, and R2 SP1, and Windows 7 Gold and SP1 on 64-bit platforms does not properly validate pointers during the parsing of OpenType (aka OTF) fonts, which allows remote attackers to execute arbitrary code via a crafted font file, aka "Win32k OTF Validation Vulnerability."
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Analysis
by VulDB Data Team • 01/13/2025
The vulnerability described in CVE-2011-1873 represents a critical pointer validation flaw within the win32k.sys kernel-mode driver component of Microsoft Windows operating systems. This vulnerability specifically affects the parsing of OpenType font files, which are commonly used for displaying text and graphics in various applications and system interfaces. The flaw exists in the kernel-mode drivers that handle font rendering operations, making it particularly dangerous as it operates at the most privileged level of the operating system. The vulnerability impacts a wide range of Windows versions including Windows XP SP2, Windows Server 2003 SP2, Windows Vista SP1 and SP2, Windows Server 2008 Gold, SP2, R2, and R2 SP1, as well as Windows 7 Gold and SP1 on 64-bit platforms, demonstrating the widespread nature of this security weakness.
The technical root cause of this vulnerability lies in the improper validation of pointers during the parsing process of OpenType font files within the win32k.sys driver. When a maliciously crafted font file is processed by the system, the kernel-mode driver fails to properly validate memory pointers, creating a condition where an attacker can manipulate memory locations to execute arbitrary code with kernel-level privileges. This pointer validation failure allows remote attackers to exploit the vulnerability by simply presenting a specially crafted font file to a vulnerable system. The flaw specifically occurs during font parsing operations, where the driver does not adequately check the validity of memory references, potentially leading to memory corruption that can be exploited to gain complete system control. This vulnerability directly maps to CWE-125, which describes out-of-bounds read conditions, and CWE-787, which addresses out-of-bounds write conditions, both of which are common in kernel-mode pointer validation flaws.
The operational impact of CVE-2011-1873 is severe and far-reaching, as it provides remote code execution capabilities with kernel-level privileges. Attackers can leverage this vulnerability to execute malicious code on targeted systems without requiring local access, making it particularly dangerous in networked environments. The vulnerability can be exploited through various attack vectors including email attachments, web downloads, or malicious websites that serve crafted font files. Once successfully exploited, the attacker gains complete control over the compromised system, potentially leading to data theft, system compromise, or further lateral movement within a network. The vulnerability's presence in multiple Windows versions means that organizations with legacy systems were particularly at risk, as these systems often lacked the latest security updates and patches. This vulnerability also aligns with ATT&CK technique T1059.007, which covers command and script interpreter, as the exploitation can lead to command execution at the highest privilege level.
Mitigation strategies for this vulnerability should include immediate application of Microsoft security patches and updates, as the vendor released specific fixes for this issue through Windows Update and Microsoft Security Response Center. Organizations should prioritize patching all affected systems, particularly those running older Windows versions that may not receive extended support. Additionally, implementing network-based protections such as firewall rules that restrict access to font file types, disabling automatic font rendering for untrusted sources, and employing application whitelisting controls can help reduce the attack surface. Security monitoring should focus on detecting unusual font processing activities or unexpected system behavior that might indicate exploitation attempts. System administrators should also consider implementing network segmentation to limit the potential impact of successful exploitation and establish robust backup and recovery procedures to minimize business disruption in case of compromise. The vulnerability serves as a reminder of the critical importance of kernel-mode security and the necessity of comprehensive vulnerability management programs that address both known and emerging threats in operating system components.