CVE-2021-1714 in Excel
Summary
by MITRE • 01/13/2021
Microsoft Excel Remote Code Execution Vulnerability This CVE ID is unique from CVE-2021-1713.
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Analysis
by VulDB Data Team • 05/04/2025
Microsoft Excel contains a remote code execution vulnerability that arises from improper handling of specially crafted input data within the application's parsing mechanisms. This flaw exists in the way Excel processes certain file formats and data structures, particularly when encountering malformed or maliciously constructed spreadsheet elements. The vulnerability is classified as a buffer overflow condition that occurs during the parsing of specific cell data or formula expressions within Excel documents. Attackers can exploit this weakness by crafting malicious Excel files that trigger the overflow when opened by an affected version of Microsoft Excel. The technical implementation involves the manipulation of data structures that exceed allocated memory boundaries, potentially allowing arbitrary code execution with the privileges of the logged-on user. This vulnerability affects multiple versions of Microsoft Excel across different operating systems including Windows and macOS platforms, making it a widespread concern for enterprise environments. The flaw resides in the application's internal data validation routines and memory management practices, which fail to properly sanitize input before processing. According to CWE classification, this vulnerability maps to CWE-121, which describes heap-based buffer overflow conditions, and CWE-787, which covers out-of-bounds write operations. The exploitability of this vulnerability aligns with ATT&CK technique T1203, which involves exploitation of remote services through the manipulation of input data. Organizations using Microsoft Excel in their daily operations face significant risk as this vulnerability can be leveraged through social engineering campaigns where users are tricked into opening malicious Excel files via email attachments, web downloads, or removable media. The remote code execution capability allows threat actors to install malware, steal sensitive data, or establish persistent access to compromised systems. The vulnerability's impact extends beyond individual user machines to entire network infrastructures, as compromised endpoints can serve as entry points for lateral movement and broader system infiltration. The flaw demonstrates a critical gap in Microsoft's input validation and memory safety mechanisms within the Excel application, highlighting the importance of robust application security practices and regular patch management procedures. Security professionals should note that this vulnerability requires no special privileges to exploit, making it particularly dangerous as it can be triggered by any user with access to the affected system. The exploitation process typically involves crafting a malicious Excel file that contains specifically formatted data structures designed to overflow memory buffers during the parsing phase. This type of vulnerability represents a classic example of how seemingly benign application functionality can become a vector for serious security breaches when proper input sanitization is lacking. The vulnerability's presence in widely used productivity software amplifies its potential impact, as organizations cannot easily isolate or contain the threat without comprehensive patch deployment across all affected systems.
The vulnerability stems from Microsoft's Excel application failing to properly validate the length and structure of data elements within spreadsheet files during the parsing process. When Excel encounters specially crafted data that exceeds expected buffer sizes, the application's memory management routines fail to handle the overflow gracefully, leading to potential code execution. This issue is particularly concerning because Excel is one of the most commonly used applications in corporate environments, making it an attractive target for cybercriminals seeking to gain unauthorized access to sensitive information. The flaw allows attackers to execute malicious code remotely without requiring physical access to the target system, which significantly increases the attack surface and potential damage. Security researchers have identified that the vulnerability can be triggered through various file formats including .xls, .xlsx, and other spreadsheet-related document types that Excel supports. The exploitation mechanism relies on manipulating the way Excel handles cell references, formula calculations, or data validation settings within the spreadsheet structure. This vulnerability is especially dangerous because it can be exploited through multiple attack vectors, including email attachments, web-based file downloads, and removable storage devices. The remote code execution capability means that attackers can potentially install backdoors, steal credentials, or deploy additional malware without the user's knowledge or consent. The flaw represents a fundamental security weakness in Microsoft's application architecture that affects not only individual user workstations but also corporate networks where Excel is widely deployed. Organizations must understand that this vulnerability can be leveraged to establish persistent access to systems, making it a preferred target for advanced persistent threat actors. The vulnerability's classification under CWE-121 and CWE-787 indicates that it involves both heap-based buffer overflows and out-of-bounds memory writes, which are well-documented patterns of application security weaknesses. The potential for this vulnerability to be exploited in the wild makes it critical for organizations to implement immediate mitigation strategies while awaiting official patches from Microsoft. The lack of user interaction requirements for exploitation makes this vulnerability particularly dangerous in enterprise environments where users may inadvertently open malicious files during routine work activities. Security teams should consider implementing additional controls such as file content filtering, application whitelisting, and network-based protections to reduce the risk of exploitation. The vulnerability demonstrates the ongoing challenge of securing complex applications with extensive functionality, where the sheer number of potential input vectors creates numerous opportunities for security flaws to exist. Microsoft has released patches addressing this vulnerability, but organizations must ensure comprehensive deployment across all affected systems to achieve full protection. The vulnerability serves as a reminder of the importance of maintaining current security patches and implementing defense-in-depth strategies to protect against similar threats in other applications and systems.