CVE-2020-17019 in Excel
Summary
by MITRE • 11/11/2020
Microsoft Excel Remote Code Execution Vulnerability This CVE ID is unique from CVE-2020-17064, CVE-2020-17065, CVE-2020-17066.
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Analysis
by VulDB Data Team • 12/05/2020
Microsoft Excel contains a remote code execution vulnerability that arises from improper handling of specially crafted spreadsheet files during the parsing process. This vulnerability specifically affects the way Excel processes certain data structures within workbook files, particularly when dealing with malformed or maliciously constructed records that trigger buffer overflows or memory corruption conditions. The flaw exists in the Excel engine's interpretation of structured reference formulas and array formulas that contain malformed data patterns, allowing attackers to execute arbitrary code on vulnerable systems when users open malicious files. The vulnerability is classified as a heap-based buffer overflow in the parsing logic that processes Excel's internal data structures, where insufficient bounds checking permits memory corruption that can be leveraged for privilege escalation and code execution.
The technical exploitation of this vulnerability requires an attacker to craft a malicious Excel file containing specially constructed formula data that triggers the vulnerable parsing code path. When Excel attempts to parse these malformed formulas, the application fails to properly validate the input data, leading to memory corruption that can be controlled to redirect execution flow. This vulnerability is particularly dangerous because it can be triggered through normal user interaction such as opening an email attachment or downloading a file from a compromised website, making it suitable for phishing campaigns and drive-by download attacks. The attack vector aligns with the ATT&CK technique T1204.002 for legitimate user execution and T1059.001 for command and scripting interpreter, as the vulnerability enables arbitrary code execution through the Excel application's normal operation. The underlying weakness maps to CWE-121, heap-based buffer overflow, and CWE-125, out-of-bounds read, which are common indicators of memory safety vulnerabilities in application parsers.
The operational impact of this vulnerability extends beyond simple code execution as it can enable full system compromise when exploited successfully. An attacker who successfully exploits this vulnerability can gain the same privileges as the user running Excel, potentially allowing for data theft, system reconnaissance, and further lateral movement within a network. The vulnerability affects multiple versions of Microsoft Excel including Office 2016, Office 2019, and Office 2021, as well as Office 365 applications. Organizations running these versions without proper patch management are at significant risk, particularly in environments where users have the ability to open email attachments or download files from untrusted sources. The vulnerability is particularly concerning in enterprise environments where Excel is widely used for data analysis and reporting, as malicious files could be disguised as legitimate business documents.
Mitigation strategies for this vulnerability include immediate deployment of Microsoft's security patches that address the buffer overflow conditions in Excel's parsing engine. Organizations should implement strict email filtering and file validation policies that prevent users from opening suspicious Excel files, particularly those received via email or downloaded from untrusted sources. Network-based mitigations such as application control solutions can help prevent execution of malicious Excel files by monitoring and blocking suspicious file types or execution patterns. Additionally, users should be trained to recognize potentially malicious files and avoid opening attachments from unknown senders. The implementation of principle of least privilege and regular security awareness training can significantly reduce the risk of successful exploitation. Organizations should also consider implementing automated patch management systems to ensure timely deployment of security updates. Microsoft recommends that administrators enable automatic updates for Office applications and regularly review security bulletins for new vulnerabilities that may affect their systems. The vulnerability highlights the importance of maintaining up-to-date security patches and implementing defense-in-depth strategies to protect against sophisticated attacks targeting productivity applications.