Source: cve@mitre.org
The Graphics Device Interface (GDI) in win32k.sys in the kernel-mode drivers 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 validate user-mode input, which allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption) via crafted data, as demonstrated by a large height attribute of an IFRAME element rendered by Safari, aka "GDI Access Violation Vulnerability."
Microsoft Windows systems are vulnerable to a critical remote code execution (RCE) vulnerability in the Graphics Device Interface (GDI) component. This flaw allows attackers to execute arbitrary code on vulnerable systems, potentially leading to complete system compromise and data exfiltration.
Step 1: Payload Delivery: The attacker crafts a malicious HTML document containing an IFRAME element with a large height attribute. This document is typically delivered via a phishing email, malicious website, or compromised web server.
Step 2: User Interaction: The victim opens the malicious HTML document using a web browser, such as Safari (as demonstrated in the original report) or potentially other browsers that utilize the Windows GDI for rendering.
Step 3: GDI Processing: The browser's rendering engine calls the Windows GDI (win32k.sys) to render the IFRAME element.
Step 4: Input Validation Failure: win32k.sys fails to properly validate the excessively large height attribute provided in the IFRAME element.
Step 5: Memory Corruption: Due to the invalid height value, the GDI attempts to allocate an excessively large memory buffer or perform calculations that lead to a buffer overflow or other memory corruption. This overwrites critical data structures in kernel memory.
Step 6: Code Execution (Exploitation): The memory corruption allows the attacker to overwrite a function pointer or other control data in kernel memory. When the corrupted function is called, the attacker's malicious code is executed in the context of the kernel, granting them elevated privileges and control over the system.
The vulnerability lies within the win32k.sys kernel-mode driver, specifically in how it handles user-mode input related to the rendering of graphical elements. The flaw stems from insufficient validation of the height attribute of an IFRAME element. By providing a crafted IFRAME with an excessively large height value, an attacker can trigger a memory corruption condition. This leads to an access violation, which can be leveraged to overwrite critical data structures in kernel memory. The root cause is a buffer overflow or similar memory management error due to the lack of bounds checking on the height attribute during GDI operations. This allows for the overwrite of adjacent memory regions, potentially including function pointers or other sensitive data, ultimately leading to arbitrary code execution. The vulnerability is triggered during the rendering process, specifically when the GDI attempts to allocate memory or perform calculations based on the invalid height value.
This vulnerability is a prime target for various threat actors due to its potential for remote code execution and system compromise. It is likely used by both state-sponsored APTs and financially motivated cybercriminals. The vulnerability's age and the availability of PoCs make it a low-hanging fruit for attackers. Not listed on CISA KEV at the time of this report, but due to the potential impact, it is a high-priority vulnerability.
Monitor for unusual network traffic patterns associated with web browsing, especially to and from untrusted sources.
Analyze system logs for unexpected crashes or errors related to win32k.sys or GDI operations.
Implement Host-Based Intrusion Detection Systems (HIDS) to monitor for suspicious process behavior, such as unexpected memory access or code injection.
Monitor for the creation of suspicious files or registry keys.
Analyze memory dumps for evidence of memory corruption or code execution within win32k.sys.
Network Intrusion Detection Systems (NIDS) can be configured to detect malicious HTML or JavaScript payloads containing IFRAME elements with excessively large height attributes, although this is a less reliable detection method.
Apply the latest security patches from Microsoft. This is the most critical step.
Implement a robust patch management strategy to ensure timely patching of all Windows systems.
Enable and configure Windows Defender or other endpoint security solutions with up-to-date signatures and behavioral analysis capabilities.
Implement a web application firewall (WAF) to filter malicious requests targeting web servers.
Educate users about the dangers of opening suspicious emails or visiting untrusted websites.
Enforce least privilege principles to limit the impact of a successful exploit.