CVE-2021-40474 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-2021-40479, CVE-2021-40485.
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Analysis
by VulDB Data Team • 10/15/2021
Microsoft Excel contains a remote code execution vulnerability that arises from improper handling of specially crafted files during the parsing process. This vulnerability specifically affects the way Excel processes certain data structures within spreadsheet files, creating a condition where malicious code can be executed remotely without user interaction. The flaw exists in the file parsing engine that fails to properly validate input data before processing it, allowing attackers to craft malicious files that trigger unintended code execution when opened by vulnerable versions of Excel. The vulnerability is particularly dangerous because it can be exploited through social engineering attacks where users are tricked into opening malicious spreadsheet files, making it a significant threat vector for enterprise environments. According to the CWE taxonomy, this vulnerability maps to CWE-129 Input Validation and OWASP Top Ten category A03: Injection, as it involves improper validation of input data leading to code execution. The remote code execution capability places this vulnerability in the ATT&CK framework under T1203 Exploitation for Client Execution, where adversaries leverage vulnerabilities in applications to execute malicious code on target systems. The attack surface is broad as Excel is widely used across organizations for data processing and analysis, making the exploitation potential substantial. The vulnerability affects multiple versions of Microsoft Excel across different operating systems, including Windows and macOS platforms, with the most significant impact occurring on systems running older versions that have not received the relevant security patches. When exploited, this vulnerability allows attackers to execute arbitrary code with the privileges of the user running Excel, potentially leading to full system compromise. The exploitation requires minimal user interaction beyond opening the malicious file, making it particularly effective in phishing campaigns. Organizations should consider the vulnerability's potential for lateral movement within networks, as compromised systems could serve as launching points for further attacks. The risk assessment indicates this vulnerability should be prioritized for immediate patching due to its remote execution capability and the widespread use of Excel in corporate environments. Microsoft has released security updates addressing this vulnerability, and administrators should ensure all systems are updated promptly to mitigate the risk of exploitation.
The technical nature of this vulnerability stems from the improper handling of memory structures during file parsing operations. When Excel encounters specially crafted data within spreadsheet files, the application fails to validate the boundaries of memory allocations, leading to buffer overflows or other memory corruption conditions. These memory issues can be exploited to overwrite critical program execution pointers or inject malicious code into the application's memory space. The vulnerability is classified as a remote code execution flaw because the malicious code execution occurs without requiring local system access or user interaction beyond opening the file. Attackers can leverage this vulnerability through various delivery mechanisms including email attachments, malicious websites, or compromised file sharing platforms. The exploitation process typically involves crafting a malicious Excel file that contains specially formatted data structures designed to trigger the memory corruption when processed by the vulnerable application. This type of vulnerability is particularly concerning because it can bypass many traditional security controls, including antivirus software, as the malicious code is executed within the legitimate application process. The vulnerability's impact extends beyond individual user systems to potentially compromise entire network infrastructures, especially when users with elevated privileges open malicious files. Security researchers have noted that the vulnerability can be particularly difficult to detect through network monitoring tools because the malicious activity occurs within the normal application execution flow. The exploitation of this vulnerability aligns with ATT&CK techniques for privilege escalation and persistence, as attackers can establish backdoors or maintain access to compromised systems. Organizations should implement layered security approaches including email filtering, application whitelisting, and regular security awareness training to reduce the risk of exploitation. The vulnerability's presence in Microsoft Excel makes it a prime target for nation-state actors and advanced persistent threat groups seeking to establish long-term access to target environments. Proper patch management and security configuration are essential defenses against this and similar vulnerabilities, as they address the root cause of the memory handling issues within the application. The remediation process requires careful coordination to ensure that all Excel installations across an organization are updated, including mobile and cloud-based deployments that may not receive updates through standard channels.