CVE-2021-40485 in Office
Summary
by MITRE • 10/13/2021
Microsoft Excel Remote Code Execution Vulnerability This CVE ID is unique from CVE-2021-40471, CVE-2021-40473, CVE-2021-40474, CVE-2021-40479.
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Analysis
by VulDB Data Team • 03/01/2025
Microsoft Excel contains a remote code execution vulnerability that arises from improper handling of specially crafted spreadsheet files during the parsing process. This flaw exists in the way Excel processes certain data structures within workbook files, particularly when dealing with malformed or maliciously constructed cells and formulas. The vulnerability stems from a lack of proper input validation and bounds checking mechanisms within Excel's parsing engine, allowing an attacker to craft malicious files that can trigger arbitrary code execution when opened by an affected version of Excel.
The technical implementation of this vulnerability involves the exploitation of memory corruption issues within Excel's internal processing routines. When a user opens a specially crafted Excel file, the application's parsing logic fails to properly validate array boundaries and memory allocation parameters, leading to buffer overflows or heap corruption conditions. This allows attackers to manipulate the execution flow of the application and potentially inject malicious code that executes with the privileges of the user running Excel. The vulnerability is particularly dangerous because it can be triggered through simple file opening operations without requiring any additional user interaction beyond the initial file access.
The operational impact of this vulnerability extends beyond simple remote code execution, as it can be leveraged to establish persistent access to target systems. Attackers can combine this vulnerability with other techniques to create sophisticated attack chains that bypass traditional security controls and defenses. The vulnerability affects multiple versions of Microsoft Excel across different operating systems, making it a significant threat to enterprise environments where spreadsheet applications are widely used. Organizations that rely heavily on Excel for data processing and analysis face heightened risk, as the attack vector can be delivered through email attachments, malicious downloads, or compromised websites.
Security professionals should implement layered mitigation strategies to protect against this vulnerability, including regular patch management and application whitelisting policies. The most effective immediate mitigation involves applying the relevant Microsoft security updates that address the underlying parsing flaws in Excel's processing engine. Network-based defenses such as email filtering and web proxies can help prevent initial delivery of malicious files, while endpoint protection solutions should be configured to monitor for suspicious Excel process behaviors. Organizations should also consider implementing macro security policies that restrict or disable potentially dangerous features, as many exploits leverage macro capabilities to achieve their objectives. According to CWE standards, this vulnerability maps to CWE-121, which describes heap-based buffer overflow conditions, and aligns with ATT&CK technique T1059.005 for command and scripting interpreter execution through office applications. The vulnerability demonstrates the critical importance of proper input validation and memory management in preventing remote code execution scenarios that can compromise entire enterprise environments.