CVE-2007-1239 in Excel
Summary
by MITRE
Microsoft Excel 2003 does not properly parse .XLS files, which allows remote attackers to cause a denial of service (application crash) via a file with a (1) corrupted XML format or a (2) corrupted XLS format, which triggers a NULL pointer dereference.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 08/25/2018
Microsoft Excel 2003 contains a critical parsing vulnerability in its handling of .XLS file formats that can be exploited to trigger a denial of service condition through carefully crafted malicious files. This vulnerability stems from inadequate input validation mechanisms within the application's file parsing engine, specifically when processing XML formatted content within Excel files. The flaw manifests when Excel encounters malformed or corrupted XML structures within .XLS containers, leading to improper memory management and eventual application instability. This vulnerability is categorized under CWE-476 which addresses NULL pointer dereferences, representing a fundamental memory safety issue where the application attempts to access memory locations that have not been properly initialized or allocated.
The technical exploitation of this vulnerability occurs through the manipulation of file format structures that Excel expects to encounter during normal operation. When a maliciously crafted .XLS file containing corrupted XML elements is opened, the parsing routine fails to properly validate the structure before attempting to dereference pointers to memory locations. This results in a NULL pointer dereference condition that causes the application to crash and terminate unexpectedly. The vulnerability affects the specific version of Excel 2003 and represents a classic example of insufficient error handling in file format parsers, where the application does not adequately protect against malformed input data that could lead to memory access violations.
From an operational perspective, this vulnerability presents significant risks to enterprise environments where Excel 2003 remains in use, particularly in legacy systems where upgrading to newer versions is not immediately feasible. The denial of service impact can be severe as it can disrupt business operations when users attempt to open legitimate files that may have been corrupted during transmission or storage processes. Attackers can leverage this vulnerability by delivering malicious files through email attachments, web downloads, or file sharing platforms, potentially causing widespread disruption across multiple user sessions. The vulnerability also aligns with ATT&CK technique T1203 which describes the use of application or system exploitation to cause denial of service conditions, making it particularly dangerous in environments where Excel is frequently used for critical business data processing.
The mitigation strategies for this vulnerability include immediate deployment of Microsoft security patches and updates that address the specific parsing flaws in Excel 2003's file handling mechanisms. Organizations should implement robust file validation procedures and consider deploying application whitelisting solutions to restrict execution of potentially malicious files. Network-based security controls such as email filtering and web proxies can help prevent delivery of malicious files to end users. Additionally, system administrators should consider implementing automated file integrity checks and monitoring for unusual file access patterns that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper input validation and error handling in software applications, particularly those dealing with complex file format parsing operations that must maintain stability even when processing malformed or corrupted data.