CVE-2017-2896 in libxls
Summary
by MITRE
An exploitable out-of-bounds write vulnerability exists in the xls_mergedCells function of libxls 1.4. . A specially crafted XLS file can cause a memory corruption resulting in remote code execution. An attacker can send malicious XLS file to trigger this vulnerability.
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Analysis
by VulDB Data Team • 01/11/2023
The vulnerability identified as CVE-2017-2896 represents a critical out-of-bounds write flaw within the libxls library version 1.4. This library serves as a crucial component for parsing Microsoft Excel file formats, particularly the older .xls format, and is widely integrated into various applications and systems that require spreadsheet data processing. The vulnerability specifically resides within the xls_mergedCells function, which handles the parsing of merged cell structures commonly found in Excel documents. When a maliciously crafted XLS file is processed by an application utilizing libxls, the function fails to properly validate array bounds during memory allocation for merged cell data structures, creating an exploitable condition that can be leveraged by remote attackers.
The technical nature of this vulnerability aligns with CWE-787, which describes out-of-bounds write conditions where a program writes data past the end of a buffer. The flaw occurs during the parsing of merged cells in Excel files where the library does not adequately validate the number of merged cell records specified in the file against the actual memory buffer size allocated for these structures. This insufficient boundary checking allows an attacker to craft an XLS file containing malformed merged cell data that, when processed by vulnerable applications, triggers memory corruption. The out-of-bounds write can overwrite adjacent memory locations, potentially corrupting critical program data structures or even allowing an attacker to inject and execute arbitrary code within the context of the vulnerable application.
The operational impact of CVE-2017-2896 extends far beyond simple data corruption, as it enables full remote code execution capabilities. This vulnerability affects any application or system that relies on libxls for Excel file processing, including web applications, document management systems, and enterprise software solutions. Attackers can leverage this vulnerability by delivering malicious XLS files through various attack vectors such as email attachments, compromised websites, or file sharing platforms. The exploitation process typically involves crafting an XLS file with carefully constructed merged cell records that cause the buffer overflow when processed by vulnerable applications. This vulnerability is particularly dangerous because it can be triggered automatically when users open or preview Excel files, making it a prime target for phishing attacks and social engineering campaigns.
From a threat modeling perspective, this vulnerability maps to several ATT&CK techniques including T1203 (Exploitation for Client Execution) and T1059 (Command and Scripting Interpreter) as attackers can execute arbitrary code through the vulnerable library. The attack surface is extensive given libxls's widespread adoption across different platforms and applications, making this vulnerability particularly impactful. Organizations using vulnerable applications may experience complete system compromise, data exfiltration, or persistent backdoor installation. The remediation process requires updating to patched versions of libxls or implementing application-level input validation and sandboxing measures. Security practitioners should prioritize identifying all systems and applications utilizing the vulnerable library, implementing network-based intrusion detection rules, and conducting thorough vulnerability assessments to ensure complete remediation across the enterprise infrastructure.