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). Exploitation allows attackers to execute arbitrary code with kernel-level privileges, potentially leading to complete system compromise and data exfiltration. This vulnerability is triggered by crafted data, such as a malformed IFRAME element, that exploits a memory corruption flaw within the GDI component.
Step 1: Payload Delivery: The attacker crafts a malicious HTML page containing an IFRAME element with a very large height attribute. This page is hosted on a malicious website or delivered via phishing or other social engineering techniques.
Step 2: User Interaction: The victim opens the malicious HTML page using a vulnerable web browser (e.g., Safari, or any browser using 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: The GDI fails to properly validate the large height attribute provided in the IFRAME element.
Step 5: Memory Corruption: Due to the invalid height, the GDI attempts to allocate or manipulate memory in a way that leads to a buffer overflow or other memory corruption. This can overwrite critical data structures or code.
Step 6: Code Execution (Exploitation): The attacker leverages the memory corruption to overwrite the instruction pointer (EIP) or other control flow mechanisms. This redirects program execution to attacker-controlled code, allowing the attacker to execute arbitrary code with kernel-level privileges.
The vulnerability stems from a lack of proper input validation within the win32k.sys driver, specifically when handling the height attribute of an IFRAME element during rendering. The GDI fails to adequately validate the size of the provided height value, leading to a buffer overflow or other memory corruption issues. This allows an attacker to overwrite critical memory regions, potentially including the instruction pointer (EIP), and redirect program execution to attacker-controlled code. The root cause is a missing or insufficient bounds check on the height parameter, allowing an excessively large value to be passed, which then corrupts memory when the GDI attempts to allocate or process resources based on this invalid size. This can lead to arbitrary code execution, denial of service (DoS), or information disclosure.