CVE-2011-1990 in SharePoint Server
Summary
by MITRE
Microsoft Excel 2007 SP2; Excel in Office 2007 SP2; Excel Viewer SP2; Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats SP2; and Excel Services on Office SharePoint Server 2007 SP2 do not properly validate the sign of an unspecified array index, which allows remote attackers to execute arbitrary code via a crafted spreadsheet, aka "Excel Out of Bounds Array Indexing Vulnerability."
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Analysis
by VulDB Data Team • 11/20/2021
The vulnerability identified as CVE-2011-1990 represents a critical out-of-bounds array indexing flaw within Microsoft Excel 2007 and related Office components. This issue affects multiple products including Excel 2007 SP2, Excel Viewer SP2, the Office Compatibility Pack, and Excel Services on SharePoint Server 2007 SP2. The vulnerability stems from inadequate validation of array index signs during spreadsheet processing, creating a condition where maliciously crafted spreadsheet files can trigger unauthorized code execution. This flaw operates at the core of Excel's file parsing mechanism, specifically targeting how the application handles array indexing operations within spreadsheet files.
The technical exploitation of this vulnerability occurs when a maliciously constructed spreadsheet file is opened, causing Excel to process an array index with an invalid sign value. This improper validation allows attackers to manipulate memory access patterns and potentially execute arbitrary code with the privileges of the affected user. The vulnerability is classified as a buffer overflow condition under CWE-129, specifically involving improper validation of array indices. This type of flaw falls under the ATT&CK technique T1203 - Exploitation for Client Execution, where adversaries leverage application vulnerabilities to execute malicious code on target systems. The out-of-bounds access can lead to memory corruption, allowing attackers to overwrite critical memory locations and redirect program execution flow.
The operational impact of this vulnerability is severe, as it enables remote code execution without requiring user interaction beyond opening the malicious file. Attackers can craft specially formatted Excel files that, when opened by victims, automatically execute malicious payloads. This makes the vulnerability particularly dangerous in enterprise environments where users frequently open spreadsheet files from external sources. The vulnerability affects not only end-user systems but also server environments running Excel Services, potentially allowing attackers to compromise entire SharePoint installations. Organizations using the Office Compatibility Pack are also at risk, as this component enables viewing of older Office file formats and is commonly deployed across enterprise networks.
Mitigation strategies for CVE-2011-1990 should focus on immediate patch deployment through Microsoft's security updates, as well as implementing defensive measures such as restricting file type execution, enabling macro security settings, and deploying application whitelisting solutions. Network segmentation and email filtering can help prevent initial compromise through malicious attachments. The vulnerability demonstrates the importance of proper input validation in Office applications and highlights the need for comprehensive security testing of file parsing components. Organizations should also implement monitoring for suspicious file access patterns and ensure all Office components are kept current with security patches. This vulnerability serves as a prime example of how seemingly minor input validation flaws can result in significant security breaches, emphasizing the critical need for robust software security practices throughout the development lifecycle.