CVE-2019-16338 in Office
Summary
by MITRE
The tfo_common component in HwordApp.dll in Hancom Office 9.6.1.7634 allows a use-after-free via a crafted .docx file.
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Analysis
by VulDB Data Team • 05/11/2025
The vulnerability identified as CVE-2019-16338 represents a critical use-after-free flaw within the tfo_common component of HwordApp.dll in Hancom Office version 9.6.1.7634. This issue arises from improper memory management practices during the processing of crafted .docx files, creating a scenario where freed memory locations are accessed after being deallocated. The vulnerability falls under the category of memory corruption vulnerabilities, specifically classified as CWE-416 which defines use-after-free conditions as a critical security weakness where program code continues to reference memory after it has been freed. The affected component resides within the word processing module of Hancom Office, making it particularly dangerous as it can be triggered through routine document handling operations.
The technical exploitation of this vulnerability occurs when a maliciously crafted .docx file is opened within the Hancom Office environment. During the parsing process of the document structure, the tfo_common component fails to properly validate memory references, leading to a situation where memory allocated for document elements is freed but subsequently accessed by the application's processing logic. This memory management failure creates a potential for arbitrary code execution, as attackers can manipulate the freed memory contents to inject and execute malicious payloads. The vulnerability demonstrates characteristics consistent with heap-based memory corruption issues that align with ATT&CK technique T1059.007 for command and scripting interpreter, as successful exploitation could enable attackers to execute arbitrary commands within the victim's system context.
The operational impact of this vulnerability extends beyond simple document processing, as it can be leveraged for complete system compromise when users open malicious documents. The attack surface is broad since .docx files are commonly shared through email attachments, file sharing platforms, and collaborative work environments where Hancom Office is deployed. Organizations using this software version face significant risk exposure, particularly in environments where users regularly open documents from untrusted sources. The vulnerability's exploitability is enhanced by the fact that it requires no special privileges to trigger, making it particularly dangerous in enterprise environments where users may have elevated access rights through legitimate document processing activities. This use-after-free condition can lead to denial of service, privilege escalation, or full system compromise depending on the execution context and target system configuration.
Mitigation strategies for CVE-2019-16338 should prioritize immediate software updates from Hancom to address the memory management flaw in the tfo_common component. System administrators should implement strict document filtering policies that prevent automatic opening of .docx files from untrusted sources, while also deploying email security solutions that can identify and quarantine potentially malicious documents. Network-based protections should include content inspection rules that can detect suspicious .docx file structures that may indicate exploitation attempts. Additionally, users should be trained to avoid opening documents from unknown senders and to verify document integrity through digital signatures where available. The vulnerability underscores the importance of regular software patching and maintaining updated security controls, as the flaw represents a classic memory corruption issue that can be addressed through proper code review and memory management practices. Organizations should also consider implementing application whitelisting policies that restrict execution of untrusted Office documents to minimize the attack surface.