CVE-2017-11884 in Excel
Summary
by MITRE
Microsoft Excel 2016 Click-to-Run (C2R) allows an attacker to run arbitrary code in the context of the current user by failing to properly handle objects in memory, aka "Microsoft Office Memory Corruption Vulnerability". This CVE ID is unique from CVE-2017-11882.
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Analysis
by VulDB Data Team • 01/23/2021
The vulnerability identified as CVE-2017-11884 represents a critical memory corruption flaw in Microsoft Excel 2016 Click-to-Run edition that enables remote code execution under specific conditions. This vulnerability falls under the broader category of memory corruption issues that have long been a primary target for cyber adversaries seeking to compromise end-user systems. The flaw specifically manifests when Excel fails to properly handle objects in memory during the processing of maliciously crafted files, creating opportunities for attackers to execute arbitrary code with the privileges of the currently logged-in user. This represents a significant security risk as it bypasses many traditional security controls and can be exploited through social engineering techniques targeting unsuspecting users. The vulnerability is particularly concerning because it affects a widely used productivity application that users frequently interact with, making it an attractive target for attackers seeking persistent access to corporate networks.
The technical implementation of this vulnerability involves improper memory handling during the parsing of specific file formats that Excel processes, particularly those involving structured data manipulation. When Excel encounters malformed or specially crafted data structures within spreadsheet files, the memory management routines fail to validate input properly, leading to memory corruption that can be leveraged by attackers to inject and execute malicious code. This type of vulnerability maps directly to CWE-125, which describes out-of-bounds read conditions, and CWE-787, which covers out-of-bounds writes in heap-based buffers. The flaw is particularly dangerous because it can be triggered through various attack vectors including email attachments, malicious websites, or compromised documents shared through collaboration platforms. Attackers typically exploit this vulnerability by crafting specially formatted Office documents that, when opened, trigger the memory corruption during Excel's processing of embedded objects or formulas, ultimately allowing for code execution without requiring user interaction beyond opening the malicious file.
The operational impact of CVE-2017-11884 extends far beyond individual system compromise, as it provides attackers with a potent tool for establishing persistent access to target networks. Once successfully exploited, the vulnerability allows adversaries to execute code in the context of the current user, which can lead to privilege escalation, data exfiltration, or the installation of additional malware components. Security researchers have documented this vulnerability being actively exploited in the wild, particularly in targeted attacks against government agencies, financial institutions, and critical infrastructure organizations. The vulnerability's exploitation aligns with tactics described in the MITRE ATT&CK framework under the 'Execution' and 'Persistence' domains, where attackers leverage legitimate system tools to execute malicious code and establish footholds within networks. Organizations that rely heavily on Microsoft Office productivity suites face significant risk from this vulnerability, especially when users receive unsolicited emails containing malicious attachments or when documents are shared through untrusted channels. The impact is further amplified by the fact that many organizations lack comprehensive email filtering and endpoint protection measures that could prevent exploitation attempts.
Mitigation strategies for CVE-2017-11884 require a multi-layered approach that combines immediate patching with defensive measures to reduce the attack surface. Microsoft released security updates that address this vulnerability, and organizations should prioritize applying these patches to all affected systems, particularly those running Excel 2016 Click-to-Run editions. Beyond patch management, security teams should implement additional controls such as disabling automatic execution of macros in Office applications, implementing strict file type filtering for email attachments, and deploying advanced endpoint protection solutions that can detect anomalous behavior patterns associated with exploitation attempts. Network segmentation and privileged access controls can help limit the potential damage from successful exploitation by preventing lateral movement within compromised networks. Organizations should also conduct regular security awareness training to educate users about recognizing potentially malicious Office documents and the importance of verifying document sources before opening attachments. The vulnerability's characteristics make it particularly susceptible to detection by behavioral analysis tools that monitor for unusual memory access patterns or unexpected code execution, which should be integrated into existing security monitoring frameworks to provide additional protection against similar memory corruption vulnerabilities.