CVE-2017-2789 in Ichitaro Office
Summary
by MITRE
When copying filedata into a buffer, JustSystems Ichitaro Office 2016 Trial will calculate two values to determine how much data to copy from the document. If both of these values are larger than the size of the buffer, the application will choose the smaller of the two and trust it to copy data from the file. This value is larger than the buffer size, which leads to a heap-based buffer overflow. This overflow corrupts an offset in the heap used in pointer arithmetic for writing data and can lead to code execution under the context of the application.
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Analysis
by VulDB Data Team • 09/02/2020
The vulnerability identified as CVE-2017-2789 represents a critical heap-based buffer overflow flaw in JustSystems Ichitaro Office 2016 Trial software. This vulnerability stems from improper buffer size validation during file data copying operations, creating a dangerous condition where the application's memory management becomes compromised. The flaw specifically manifests when the software processes document data and attempts to copy information into a predetermined buffer structure.
The technical implementation of this vulnerability involves a flawed calculation mechanism that determines the amount of data to copy from a document file. During the copying process, the application calculates two separate values to establish the copy size limit, but fails to properly validate these values against the actual buffer boundaries. When both calculated values exceed the buffer size, the software incorrectly selects the smaller value for the copy operation while still trusting this value to be safe for execution. This selection process creates a scenario where data exceeding the buffer capacity gets copied, resulting in heap corruption that fundamentally undermines memory integrity.
The operational impact of this vulnerability extends beyond simple data corruption, as it creates a potential code execution vector that operates under the privileges of the compromised application. The heap-based buffer overflow specifically targets the heap memory structures used for pointer arithmetic operations, which means that attackers can manipulate memory offsets to redirect program execution flow. This type of vulnerability falls under the Common Weakness Enumeration category CWE-121, which classifies heap-based buffer overflows as a critical memory safety issue that can lead to arbitrary code execution. The attack surface becomes particularly dangerous because the application context provides elevated privileges that can be leveraged for further system compromise.
The exploitation of this vulnerability requires careful crafting of malicious input data that triggers the specific buffer calculation logic. Attackers must construct document files that contain carefully sized data structures to ensure both calculated values exceed the buffer boundaries while maintaining the smaller value selection behavior. This vulnerability aligns with ATT&CK technique T1059.007, which covers the use of command and scripting interpreters, as successful exploitation could lead to arbitrary code execution within the application's execution context. The memory corruption affects heap management structures that are fundamental to the application's operation, making this a particularly severe vulnerability that could be exploited for privilege escalation or persistent access.
Mitigation strategies for CVE-2017-2789 should focus on immediate patch deployment from JustSystems, as the vendor has released updates addressing the buffer validation logic. Organizations should implement network segmentation and application whitelisting to limit exposure, particularly in environments where document processing is frequent. Input validation measures should be enhanced to prevent malformed data from reaching the vulnerable parsing functions, while regular security assessments can help identify similar buffer overflow patterns in other software components. The vulnerability demonstrates the importance of proper bounds checking and memory management practices, particularly in applications that process untrusted document formats, and serves as a reminder of the critical need for robust software security testing throughout the development lifecycle.