CVE-2000-0637 in Excel
Summary
by MITRE
Microsoft Excel 97 and 2000 allows an attacker to execute arbitrary commands by specifying a malicious .dll using the Register.ID function, aka the "Excel REGISTER.ID Function" vulnerability.
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Analysis
by VulDB Data Team • 05/20/2019
The CVE-2000-0637 vulnerability represents a critical security flaw in Microsoft Excel 97 and 2000 versions that enables remote code execution through malicious dynamic link library files. This vulnerability specifically targets the Register.ID function within Excel's macro execution environment, creating a pathway for attackers to escalate privileges and compromise systems. The flaw exists due to insufficient input validation and improper handling of external library references within the spreadsheet application's macro processing capabilities.
The technical exploitation of this vulnerability occurs when an Excel spreadsheet contains a malicious Register.ID function call that references a specially crafted .dll file. When the vulnerable Excel application processes this macro, it loads and executes the malicious dynamic link library without proper security checks or sandboxing mechanisms. This behavior stems from the application's trust model that allows arbitrary code loading from external sources, particularly when the Register.ID function is used to register external procedures. The vulnerability is classified under CWE-74 as a 'Improper Neutralization of Special Elements in Output Used by a Downstream Component' and relates to CWE-121 as 'Stack-based Buffer Overflow', demonstrating how improper input handling can lead to code execution.
The operational impact of this vulnerability extends beyond simple remote code execution to encompass full system compromise and potential lateral movement within network environments. An attacker who successfully exploits this vulnerability can gain complete control over the affected system, including the ability to install additional malware, modify system configurations, or establish persistent backdoors. The vulnerability is particularly dangerous because it can be delivered through seemingly legitimate spreadsheet files, making it difficult for users to distinguish between benign and malicious documents. This makes the attack vector highly effective for phishing campaigns and social engineering attacks targeting office environments.
Mitigation strategies for CVE-2000-0637 should focus on immediate application of Microsoft security patches and comprehensive system hardening measures. Organizations must ensure that all Excel installations are updated to the latest security patches provided by Microsoft, as the vulnerability was addressed through proper input validation and enhanced library loading mechanisms. Network administrators should implement macro security policies that restrict or disable macro execution in potentially untrusted documents, while also deploying application whitelisting solutions to prevent unauthorized .dll loading. The ATT&CK framework categorizes this vulnerability under T1059.005 for 'Command and Scripting Interpreter: Visual Basic', highlighting the need for comprehensive endpoint protection and monitoring for suspicious macro behavior. Additionally, security awareness training should emphasize the dangers of opening spreadsheet files from untrusted sources, and network segmentation should be implemented to limit the potential impact of successful exploitation attempts.