CVE-2016-4294 in Office
Summary
by MITRE
When opening a Hangul Hcell Document (.cell) and processing a property record within the Workbook stream, Hancom Office 2014 will attempt to allocate space for an element using a length from the file. When copying user-supplied data to this buffer, however, the application will use a different size which leads to a heap-based buffer overflow. This vulnerability can lead to code-execution under the context of the application.
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Analysis
by VulDB Data Team • 04/20/2025
The vulnerability identified as CVE-2016-4294 represents a critical heap-based buffer overflow in Hancom Office 2014, specifically within its handling of Hangul Hcell Document files with the .cell extension. This flaw occurs during the processing of property records within the Workbook stream, where the application's memory management mechanisms fail to properly validate buffer allocation sizes. The vulnerability stems from a fundamental mismatch between the allocated buffer size and the actual data copying operation that follows, creating a condition where user-supplied data can overwrite adjacent memory regions.
The technical implementation of this vulnerability involves a classic buffer overflow scenario where the application first allocates memory based on a length value extracted from the malicious file structure. However, when copying data to this allocated buffer, the application employs a different size parameter that exceeds the originally allocated space. This discrepancy creates a heap corruption condition that can be exploited by attackers to execute arbitrary code within the application's security context. The flaw demonstrates poor input validation and memory management practices that are commonly classified under CWE-121, heap-based buffer overflow, and CWE-122, heap-based buffer overflow, where the buffer overflow occurs in heap memory rather than stack memory.
From an operational perspective, this vulnerability presents a significant risk to users who may inadvertently open malicious .cell files, particularly in environments where office productivity software is widely used. The exploitability of this vulnerability is enhanced by the fact that it occurs during normal document opening operations, requiring no special privileges or complex attack vectors. The code execution occurs under the privileges of the Hancom Office application, which typically runs with the user's permissions, potentially allowing attackers to perform actions such as installing malware, accessing sensitive data, or escalating privileges within the compromised system. This vulnerability aligns with ATT&CK technique T1203, Exploitation for Client Execution, where adversaries leverage application vulnerabilities to execute malicious code on target systems.
The impact of this vulnerability extends beyond simple code execution, as it can lead to complete system compromise when combined with other exploitation techniques or when the affected application has elevated privileges. Organizations using Hancom Office 2014 should consider the broader implications of this vulnerability within their security posture, particularly in environments where users may encounter untrusted document files. The vulnerability's exploitation potential makes it a target for both automated attacks and targeted campaigns, as the conditions for exploitation are relatively straightforward and do not require advanced technical knowledge. Mitigation strategies should include immediate patching of the affected software, implementation of document filtering policies, and user education regarding the dangers of opening untrusted Office documents. The vulnerability also highlights the importance of proper memory management practices in office productivity software and demonstrates how seemingly minor implementation flaws can result in severe security consequences.