CVE-2016-4295 in Office
Summary
by MITRE
When opening a Hangul Hcell Document (.cell) and processing a particular record within the Workbook stream, an index miscalculation leading to a heap overlow can be made to occur in Hancom Office 2014. The vulnerability occurs when processing data for a formula used to render a chart via the HncChartPlugin.hplg library. Due to a lack of bounds-checking when incrementing an index that is used for writing into a buffer for formulae, the application can be made to write pointer data outside its bounds which 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 described in CVE-2016-4295 represents a critical heap buffer overflow flaw affecting Hancom Office 2014 when processing specific Hangul Hcell Document files. This issue manifests during the handling of chart rendering operations through the HncChartPlugin.hplg library, where the application fails to properly validate index calculations when processing formula data within the Workbook stream. The flaw originates from inadequate bounds-checking mechanisms that govern how indices are incremented during buffer operations, creating a scenario where memory access exceeds allocated boundaries. This particular vulnerability demonstrates the classic characteristics of a buffer overflow condition that can be exploited to achieve arbitrary code execution within the application's security context, making it a significant threat to system integrity and user security.
The technical exploitation of this vulnerability occurs when a maliciously crafted .cell file triggers the processing of a specific record within the Workbook stream that contains formula data for chart rendering. The miscalculation of index values leads to a situation where pointer data is written beyond the intended buffer boundaries, potentially overwriting adjacent memory locations including return addresses, function pointers, or other critical control data structures. This heap overflow condition provides attackers with the opportunity to manipulate program execution flow by overwriting memory contents with malicious payloads, effectively allowing remote code execution under the privileges of the Hancom Office application process. The vulnerability specifically targets the HncChartPlugin.hplg library, indicating that the flaw is embedded within the chart rendering component of the office suite, making it particularly dangerous as it can be triggered through normal document opening procedures.
From an operational perspective, this vulnerability presents a severe risk to organizations relying on Hancom Office 2014 as their primary office suite, as it can be exploited through social engineering attacks involving malicious .cell files delivered via email attachments or compromised websites. The attack vector requires minimal user interaction beyond opening the infected document, making it particularly effective for targeted attacks against specific organizations or individuals. The exploitation can result in complete system compromise, as the code execution occurs within the application context with elevated privileges, potentially allowing attackers to establish persistent backdoors, exfiltrate sensitive data, or deploy additional malicious software. The vulnerability's impact extends beyond individual user systems to enterprise environments where document sharing and collaboration are common practices, creating widespread potential for security breaches.
Security mitigations for CVE-2016-4295 should focus on immediate patching of the Hancom Office 2014 application to address the index miscalculation and bounds-checking deficiencies within the HncChartPlugin.hplg library. Organizations should implement strict file validation policies that prevent automatic execution of potentially malicious documents, particularly those originating from untrusted sources. Network-based protections such as email filtering systems should be configured to block .cell file attachments and suspicious document content. Additionally, security awareness training should be conducted to educate users about the risks of opening unexpected document attachments and the importance of verifying document sources before processing. The vulnerability aligns with CWE-121, heap-based buffer overflow, and maps to ATT&CK technique T1059 for command and scripting interpreter, as successful exploitation would likely involve executing malicious code through the compromised application process. System administrators should also consider implementing application whitelisting policies and monitoring for unusual memory access patterns that might indicate exploitation attempts.