CVE-2006-1540 in Office
Summary
by MITRE
MSO.DLL in Microsoft Office 2000, Office XP (2002), and Office 2003 allows user-assisted attackers to cause a denial of service and execute arbitrary code via multiple attack vectors, as originally demonstrated using a crafted document record with a malformed string, as demonstrated by replacing a certain "01 00 00 00" byte sequence with an "FF FF FF FF" byte sequence, possibly causing an invalid array index, in (1) an Excel .xls document, which triggers an access violation in ole32.dll; (2) an Excel .xlw document, which triggers an access violation in excel.exe; (3) a Word document, which triggers an access violation in mso.dll in winword.exe; and (4) a PowerPoint document, which triggers an access violation in powerpnt.txt. NOTE: after the initial disclosure, this issue was demonstrated by triggering an integer overflow using an inconsistent size for a Unicode "Sheet Name" string.
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Analysis
by VulDB Data Team • 01/20/2025
The vulnerability described in CVE-2006-1540 represents a critical security flaw affecting multiple Microsoft Office applications including Office 2000, Office XP, and Office 2003. This vulnerability manifests through MSO.DLL component and exploits memory corruption issues that can be triggered by manipulating document records containing malformed strings. The attack vector requires user interaction as the malicious document must be opened by an unsuspecting user, making this a classic user-assisted remote code execution vulnerability. The flaw specifically targets the handling of Unicode string data within Office document formats, particularly affecting Excel worksheets and Word/Presentation documents through different execution paths.
The technical implementation of this vulnerability involves manipulating specific byte sequences within document structures to trigger invalid memory access conditions. The original demonstration used a simple byte replacement technique where a legitimate "01 00 00 00" sequence was replaced with "FF FF FF FF" to cause an invalid array index. This manipulation specifically affected Excel .xls documents causing access violations in ole32.dll, Excel .xlw documents triggering violations in excel.exe, Word documents causing issues in mso.dll within winword.exe, and PowerPoint documents resulting in access violations in powerpnt.txt. The vulnerability essentially creates a condition where the application attempts to access memory locations outside the valid array bounds, leading to unpredictable behavior including crashes or potential code execution.
From an operational impact perspective, this vulnerability represents a significant threat to enterprise environments where Microsoft Office applications are extensively used. The denial of service component can disrupt business operations through application crashes and system instability, while the arbitrary code execution capability provides attackers with potential access to compromised systems. The vulnerability affects multiple Office applications simultaneously, increasing the attack surface and making it particularly dangerous for organizations with diverse Office usage patterns. The integer overflow condition that was later demonstrated adds another dimension to the attack surface, as integer overflows are commonly exploited in buffer overflow scenarios and can lead to more sophisticated exploitation techniques.
This vulnerability maps to CWE-129, which describes improper validation of array indices, and CWE-125, which covers out-of-bounds read conditions. The attack patterns align with ATT&CK techniques including T1203 (Exploitation for Client Execution) and T1059 (Command and Scripting Interpreter) where attackers leverage application vulnerabilities to execute malicious code. The fact that this vulnerability affects multiple Office applications demonstrates the interconnected nature of Microsoft Office components and how a flaw in one component can impact the entire Office suite. Organizations should implement multiple layers of defense including application whitelisting, user education, and regular security updates to mitigate this type of vulnerability effectively. The vulnerability also highlights the importance of proper input validation and bounds checking in application code, particularly when handling user-supplied data in document formats.