CVE-2011-0098 in Excel
Summary
by MITRE
Integer signedness error in Microsoft Excel 2002 SP3, 2003 SP3, 2007 SP2, and 2010; Office 2004 and 2008 for Mac; Open XML File Format Converter for Mac; Excel Viewer SP2; and Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats SP2 allows remote attackers to execute arbitrary code via an XLS file with a large record size, aka "Excel Heap Overflow Vulnerability."
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Analysis
by VulDB Data Team • 11/02/2021
The CVE-2011-0098 vulnerability represents a critical integer signedness error that affects multiple versions of Microsoft Excel and related Office applications across different platforms. This flaw manifests in the handling of record sizes within XLS file format parsing, creating a condition where attackers can manipulate file structures to trigger memory corruption. The vulnerability specifically impacts Microsoft Excel 2002 SP3, 2003 SP3, 2007 SP2, 2010, Office 2004 and 2008 for Mac, Open XML File Format Converter for Mac, Excel Viewer SP2, and the Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats SP2. The issue stems from improper validation of record size parameters during file parsing operations, where signed integer variables are used in contexts that could accommodate unsigned values, leading to unexpected behavior when large values are processed.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious XLS file containing a record with an excessively large size parameter that exceeds the expected range for signed integers. When Microsoft Excel attempts to parse this record, the signedness error causes the application to allocate insufficient memory or perform incorrect calculations based on the malformed size value. This misinterpretation results in heap-based buffer overflows, where memory is overwritten beyond allocated boundaries, potentially allowing remote code execution. The vulnerability is classified under CWE-190 as an Integer Overflow or Wraparound, specifically involving signed integer handling, and aligns with ATT&CK technique T1203 for Exploitation for Execution through malicious file attachments. The flaw demonstrates how improper input validation can create dangerous conditions in memory management, particularly when dealing with legacy file format parsers that have not been updated to properly handle edge cases in integer arithmetic.
The operational impact of this vulnerability extends beyond simple exploitation, as it represents a significant threat vector for targeted attacks against enterprise environments where Excel is commonly used for document sharing and collaboration. Attackers can leverage this vulnerability through social engineering campaigns distributing malicious spreadsheets via email attachments, web downloads, or compromised document repositories. The remote execution capability means that victims do not need to be physically present or have specific privileges to be compromised, making the attack surface particularly wide. Organizations using older versions of Office applications are especially vulnerable since these products often lack modern exploit mitigations such as address space layout randomization and data execution prevention. The vulnerability also highlights the challenges of maintaining security in legacy software environments where updates may be delayed or restricted due to compatibility concerns with existing business processes.
Mitigation strategies for CVE-2011-0098 should focus on immediate patching of affected software versions, as Microsoft released security updates addressing this specific integer signedness error. Organizations should implement strict file validation policies that scan and filter potentially malicious Excel files before they reach end users, particularly in high-risk environments such as financial institutions or government agencies. Network-based protections including email filtering systems and web proxies should be configured to block suspicious XLS file attachments and monitor for known malicious file patterns. Additionally, implementing application whitelisting controls can prevent unauthorized Office applications from executing, while regular security awareness training helps users identify potential phishing attempts involving malicious spreadsheet files. The vulnerability serves as a reminder of the importance of keeping legacy software updated and the need for comprehensive vulnerability management programs that address both current and historical security flaws in enterprise software ecosystems.