CVE-2017-12110 in libxls
Summary
by MITRE
An exploitable integer overflow vulnerability exists in the xls_appendSST function of libxls 1.4.A specially crafted XLS file can cause memory corruption resulting in remote code execution.
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Analysis
by VulDB Data Team • 01/11/2023
The vulnerability identified as CVE-2017-12110 represents a critical integer overflow flaw within the libxls library version 1.4, specifically within the xls_appendSST function. This library serves as a crucial component for parsing Microsoft Excel .xls files across numerous applications and systems, making it a prime target for exploitation. The flaw stems from inadequate input validation and overflow handling when processing the Shared String Table (SST) portion of Excel files, which stores text data used throughout the spreadsheet. When a maliciously crafted XLS file is processed by software utilizing libxls, the vulnerability manifests during the parsing of string data, creating conditions where integer arithmetic operations exceed their maximum representable values.
The technical implementation of this vulnerability involves the xls_appendSST function failing to properly validate or constrain integer values when calculating memory allocation for string storage. This allows an attacker to craft an XLS file containing malformed SST entries that trigger integer overflow conditions. When the library attempts to allocate memory based on these overflowed values, it results in heap-based memory corruption that can be leveraged for arbitrary code execution. The vulnerability's exploitation requires the target system to process a specially crafted XLS file through an application that utilizes libxls for file parsing, making it particularly dangerous in environments where users might encounter untrusted spreadsheet files. This type of vulnerability maps directly to CWE-190, which specifically addresses integer overflow conditions, and aligns with ATT&CK technique T1203, focusing on exploitation of software vulnerabilities for code execution.
The operational impact of CVE-2017-12110 extends far beyond simple memory corruption, as it enables remote code execution capabilities that can compromise entire systems. Attackers can leverage this vulnerability to execute malicious code with the privileges of the victim application, potentially leading to complete system compromise. The vulnerability affects any software that relies on libxls version 1.4 for XLS file processing, including but not limited to office suites, document viewers, and enterprise applications that handle spreadsheet data. The remote execution aspect means that attackers can deliver malicious XLS files through email attachments, web downloads, or file sharing platforms without requiring local system access. Organizations using affected applications face significant risk, as this vulnerability can be exploited through social engineering campaigns targeting unsuspecting users who open malicious spreadsheets. The exploitation process typically requires minimal user interaction beyond opening the compromised file, making it particularly dangerous for enterprise environments where users may inadvertently execute malicious code.
Mitigation strategies for CVE-2017-12110 primarily focus on immediate remediation through software updates and patches provided by the libxls maintainers. System administrators should prioritize upgrading to libxls versions that have addressed this integer overflow vulnerability, as the original 1.4 release contains no built-in protections against such attacks. Network security measures including email filtering and web content filtering can help prevent users from accessing malicious XLS files, while endpoint protection solutions should be configured to scan for suspicious file content. Additional defensive measures include implementing application whitelisting policies to restrict which applications can process spreadsheet files, and establishing secure file handling procedures that validate file integrity before processing. Organizations should also consider disabling automatic file opening features in email clients and web browsers, as these can inadvertently trigger the vulnerability. The vulnerability's classification as a remote code execution flaw makes comprehensive network monitoring essential for detecting potential exploitation attempts, and incident response procedures should be updated to include specific protocols for handling potential exploitation of this CVE. Regular vulnerability assessments and penetration testing should be conducted to identify other potential entry points that might leverage similar integer overflow patterns in other software libraries.