CVE-2008-3471 in Excel
Summary
by MITRE
Stack-based buffer overflow in Microsoft Excel 2000 SP3, 2002 SP3, 2003 SP2 and SP3, and 2007 Gold and SP1; Office Excel Viewer 2003 SP3; Office Excel Viewer; Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats Gold and SP1; Office 2004 and 2008 for Mac; and Open XML File Format Converter for Mac allows remote attackers to execute arbitrary code via a BIFF file with a malformed record that triggers a user-influenced size calculation, aka "File Format Parsing Vulnerability."
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Analysis
by VulDB Data Team • 08/18/2019
This vulnerability represents a critical stack-based buffer overflow affecting multiple versions of Microsoft Excel and related Office applications, with implications spanning from Windows desktop environments to Mac operating systems. The flaw resides in the parsing of BIFF (Binary Interchange File Format) files, which serves as the native file format for Microsoft Excel documents. Attackers can exploit this weakness by crafting malicious BIFF files containing malformed records that manipulate size calculations during file processing, leading to memory corruption and potential code execution. The vulnerability affects not only the core Excel applications but also various viewer versions and compatibility packs, demonstrating the widespread nature of the flaw across Microsoft's Office ecosystem. This issue specifically targets the file format parsing engine's handling of user-controlled data, where the application calculates buffer sizes based on information provided in the malicious file structure.
The technical mechanism of exploitation involves the application's failure to properly validate or constrain input data during BIFF file processing, particularly when handling record headers that contain size indicators. When Excel encounters a malformed record with an oversized or malformed size field, it performs an incorrect buffer allocation that exceeds the allocated stack space, resulting in a stack overflow condition. This overflow corrupts adjacent memory locations including return addresses and function pointers, allowing attackers to redirect execution flow to malicious code injected into the buffer. The vulnerability is particularly dangerous because it can be triggered through automated means, such as email attachments or web downloads, making it a prime candidate for drive-by attacks. The attack vector requires no user interaction beyond opening the malicious file, as the vulnerability occurs during the file parsing process itself, which is typically initiated automatically when users open documents.
The operational impact of this vulnerability extends across multiple attack surfaces and deployment scenarios, affecting organizations using various Microsoft Office versions across different platforms and operating systems. Security researchers have classified this issue under CWE-121, which describes stack-based buffer overflow conditions, and it aligns with ATT&CK technique T1059.007 for command and scripting interpreter execution. Organizations running affected versions of Microsoft Excel face significant risk of remote code execution, which could lead to complete system compromise, data exfiltration, and lateral movement within network environments. The vulnerability's presence in Office Viewer applications and compatibility packs means that even systems that do not directly use Excel can be vulnerable, as these components are often installed to support document compatibility. The widespread deployment of affected Office versions across enterprise networks makes this vulnerability particularly attractive to threat actors seeking mass exploitation opportunities.
Mitigation strategies for this vulnerability should focus on immediate patching of affected systems, as Microsoft released security updates specifically addressing this issue in their regular security bulletins. Organizations should implement network-level controls such as email filtering and web proxy configurations to prevent access to potentially malicious BIFF files, particularly those originating from untrusted sources. Application whitelisting and sandboxing techniques can provide additional defense-in-depth layers, ensuring that even if a malicious file is opened, the execution environment prevents unauthorized code execution. System administrators should also consider disabling automatic opening of Office documents from untrusted sources and implementing strict file type validation at network boundaries. Regular security awareness training for end users remains crucial, as social engineering remains a common delivery method for these types of attacks. The vulnerability demonstrates the importance of maintaining up-to-date security patches and the risks associated with legacy software versions that may no longer receive security updates, emphasizing the need for comprehensive software lifecycle management policies.