CVE-2011-1989 in Office
Summary
by MITRE
Microsoft Excel 2003 SP3 and 2007 SP2; Excel in Office 2007 SP2; Excel 2010 Gold and SP1; Excel in Office 2010 Gold and SP1; Office 2004, 2008, and 2011 for Mac; Open XML File Format Converter for Mac; Excel Viewer SP2; Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats SP2; Excel Services on Office SharePoint Server 2007 SP2; Excel Services on Office SharePoint Server 2010 Gold and SP1; and Excel Web App 2010 Gold and SP1 do not properly parse conditional expressions associated with formatting requirements, which allows remote attackers to execute arbitrary code via a crafted spreadsheet, aka "Excel Conditional Expression Parsing Vulnerability."
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 11/20/2021
This vulnerability represents a critical buffer overflow condition in Microsoft Excel's handling of conditional formatting expressions within spreadsheet files. The flaw exists in the parsing mechanism that processes conditional formatting rules associated with Excel's visual presentation features. When Excel encounters malformed conditional expressions in spreadsheet files, the application fails to properly validate input parameters before processing them, creating an exploitable condition that can be leveraged by remote attackers to execute arbitrary code on affected systems.
The technical implementation of this vulnerability stems from improper bounds checking within Excel's conditional expression parser. When Excel processes conditional formatting rules, it does not adequately validate the length and structure of input data, allowing attackers to craft malicious spreadsheet files that contain oversized or malformed conditional expression data. This condition is particularly dangerous because conditional formatting is commonly used in business environments and spreadsheets are frequently shared through email attachments, network drives, and web-based collaboration platforms. The vulnerability affects multiple versions of Microsoft Office across different platforms including Windows and Mac operating systems, making it a widespread concern for enterprise environments.
From an operational perspective, this vulnerability enables attackers to achieve remote code execution without requiring user interaction beyond opening the malicious spreadsheet file. The attack vector typically involves social engineering campaigns where users receive infected spreadsheets through phishing emails or compromised web downloads. Once opened, the malicious conditional expressions trigger the buffer overflow condition, allowing attackers to inject and execute malicious code with the privileges of the affected user. This makes the vulnerability particularly attractive to threat actors seeking to establish persistent access to corporate networks through endpoint compromise.
The vulnerability maps directly to CWE-121, which describes heap-based buffer overflow conditions, and aligns with ATT&CK technique T1059.005 for command and scripting interpreter execution. Organizations affected by this vulnerability face significant risk of data breaches, system compromise, and potential lateral movement within their networks. The exploitability of this vulnerability is enhanced by the widespread use of Microsoft Excel in business environments, where users regularly open spreadsheet files from untrusted sources without proper security awareness training. The impact extends beyond individual system compromise to include potential disruption of business operations, data loss, and regulatory compliance violations.
Mitigation strategies should focus on immediate patch deployment for all affected Office versions, including the Office 2004, 2008, and 2011 for Mac platforms. Network administrators should implement email filtering solutions to block suspicious spreadsheet attachments and consider disabling automatic execution of macros in Excel environments. Additionally, users should be trained to avoid opening spreadsheet files from untrusted sources and to maintain current security patches for all Microsoft Office applications. Organizations should also consider implementing application whitelisting policies and monitoring for suspicious file execution patterns in their network security solutions to detect potential exploitation attempts.