CVE-2017-12111 in libxls
Summary
by MITRE
An exploitable out-of-bounds vulnerability exists in the xls_addCell function of libxls 1.4. A specially crafted XLS file with a formula record can cause memory corruption resulting in remote code execution. An attacker can send a malicious XLS file to trigger this vulnerability.
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Analysis
by VulDB Data Team • 01/11/2023
The vulnerability identified as CVE-2017-12111 represents a critical out-of-bounds write condition within the libxls library version 1.4, specifically within the xls_addCell function. This flaw arises from inadequate input validation when processing Microsoft Excel file format records, particularly formula records that contain malformed data structures. The libxls library serves as a parser for xls spreadsheet files, commonly used in various applications for reading and processing legacy excel formats. When an application processes a maliciously crafted xls file containing a specially constructed formula record, the xls_addCell function fails to properly bounds-check array accesses, leading to memory corruption that can be exploited for remote code execution. This vulnerability demonstrates a classic buffer overflow scenario where the library attempts to write data beyond the allocated memory boundaries, potentially allowing attackers to overwrite adjacent memory regions with malicious code or control structures.
The technical exploitation of this vulnerability leverages the fundamental weakness in memory management within the xls_addCell function, which operates under CWE-129 weakness classification as an improper input validation issue. The flaw occurs during the parsing of formula records within xls files, where the application does not validate the size or structure of formula data before attempting to store it in memory buffers. This vulnerability directly maps to ATT&CK technique T1203 - Exploitation for Client Execution, as it enables remote code execution through malicious file delivery. The vulnerability is particularly dangerous because it can be triggered simply by opening a malicious xls file in any application that uses the vulnerable libxls library, making it a widespread threat across numerous software platforms that rely on this library for spreadsheet processing functionality.
The operational impact of CVE-2017-12111 extends beyond immediate code execution capabilities to encompass broader system compromise scenarios. Attackers can craft malicious xls files that, when opened by vulnerable applications, provide remote code execution capabilities without requiring user interaction beyond the simple act of opening the file. This makes the vulnerability particularly attractive for phishing campaigns and social engineering attacks where users might unknowingly open malicious files. The memory corruption resulting from this out-of-bounds write can lead to various outcomes including application crashes, data corruption, or full system compromise depending on the execution environment and memory layout. Organizations using applications that depend on libxls 1.4 for processing spreadsheet files are at risk, including office automation systems, data analysis platforms, and any software that handles xls file formats. The vulnerability's remote exploitation capability means that attackers can compromise systems from distant locations without requiring physical access or local network presence, making it a significant threat in enterprise environments where spreadsheet processing is common.
Mitigation strategies for CVE-2017-12111 focus on immediate library updates and application-level protections. The primary recommendation involves upgrading to libxls version 1.4.1 or later, which contains the necessary patches to address the out-of-bounds write condition in the xls_addCell function. Organizations should also implement strict file validation policies that scan and validate all incoming xls files before processing, particularly in environments where users might receive files from untrusted sources. Network-level protections such as email filtering and web application firewalls can help prevent malicious xls files from reaching end users. Additionally, application developers should implement defensive programming practices including bounds checking, memory sanitization, and input validation to prevent similar issues in custom code that interfaces with spreadsheet libraries. The vulnerability highlights the importance of keeping third-party libraries updated and implementing proper security testing procedures including fuzzing and static analysis to identify potential memory corruption issues before they can be exploited by malicious actors.