CVE-2017-7856 in LibreOffice
Summary
by MITRE
LibreOffice before 2017-03-11 has an out-of-bounds write caused by a heap-based buffer overflow in the SVMConverter::ImplConvertFromSVM1 function in vcl/source/gdi/svmconverter.cxx.
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Analysis
by VulDB Data Team • 11/29/2022
The vulnerability CVE-2017-7856 represents a critical heap-based buffer overflow in LibreOffice versions prior to 2017-03-11, specifically within the SVMConverter::ImplConvertFromSVM1 function located in vcl/source/gdi/svmconverter.cxx. This flaw resides in the graphical device interface component of LibreOffice, which handles vector graphics and drawing operations. The vulnerability manifests when processing certain malformed SVM (Scalable Vector Graphics) files, creating a condition where an application can write data beyond the boundaries of allocated heap memory. Such out-of-bounds write conditions are particularly dangerous as they can lead to arbitrary code execution or application crashes, making them a prime target for exploitation by malicious actors.
The technical implementation of this vulnerability stems from insufficient input validation and boundary checking within the SVM conversion process. When LibreOffice encounters an SVM file with malformed data structures, the SVMConverter::ImplConvertFromSVM1 function fails to properly validate the size of incoming data before attempting to copy it into fixed-size buffers. This results in memory corruption that can overwrite adjacent heap allocations, potentially corrupting critical data structures or even allowing attackers to inject and execute malicious code. The flaw directly corresponds to CWE-121, which describes heap-based buffer overflow conditions, and represents a classic example of unsafe memory handling practices that violate fundamental security principles.
The operational impact of CVE-2017-7856 extends beyond simple application instability, as it creates a significant attack surface for remote code execution. An attacker could craft a malicious SVM file and distribute it through various channels including email attachments, web downloads, or document sharing platforms. When a victim opens such a file in an affected LibreOffice version, the buffer overflow occurs during the rendering process, potentially allowing remote code execution with the privileges of the user running the application. This vulnerability affects the core functionality of LibreOffice's graphic rendering engine and impacts all operating systems where the vulnerable version is installed, making it particularly concerning for enterprise environments where document processing is common. The flaw operates at the system level through the vcl (Virtual Component Library) component, which is fundamental to LibreOffice's graphical user interface and rendering capabilities.
Mitigation strategies for CVE-2017-7856 primarily focus on immediate remediation through software updates, with users and organizations required to upgrade to LibreOffice version 2017-03-11 or later where the vulnerability has been patched. The fix implemented by The Document Foundation addresses the root cause by adding proper input validation and boundary checking within the SVM conversion function, ensuring that data sizes are properly verified before memory operations occur. Additionally, organizations should implement defensive measures including email filtering rules to block suspicious document attachments, disable automatic opening of documents from untrusted sources, and maintain updated antivirus signatures that can detect malicious SVM files. From an ATT&CK framework perspective, this vulnerability maps to techniques involving execution through exploitation of software vulnerabilities, specifically T1203 for Exploitation for Execution and T1059 for Command and Scripting Interpreter, as attackers could leverage this flaw to establish persistent access through remote code execution. Network segmentation and privilege separation can also reduce the potential impact of exploitation by limiting the scope of successful attacks and preventing lateral movement within compromised systems.