CVE-2018-20304 in libexcel
Summary
by MITRE
wbook_addworksheet in workbook.c in libexcel.a in libexcel 0.01 allows attackers to cause a denial of service (SEGV) via a long second argument. NOTE: this is not a Microsoft product.
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Analysis
by VulDB Data Team • 04/22/2020
The vulnerability identified as CVE-2018-20304 resides within the libexcel library, specifically in the wbook_addworksheet function located in workbook.c within the libexcel.a archive. This flaw represents a classic buffer overflow condition that manifests as a segmentation fault when processing malformed input data. The vulnerability occurs when an attacker supplies an excessively long second argument to the wbook_addworksheet function, which triggers memory corruption and subsequently leads to a system crash or denial of service condition. The affected library is a third-party component not manufactured by Microsoft, making this an independent software vulnerability that affects applications relying on libexcel for spreadsheet processing functionality.
This vulnerability maps to CWE-121 as it involves a classic stack-based buffer overflow condition where insufficient bounds checking allows arbitrary data to overwrite adjacent memory locations. The flaw demonstrates characteristics consistent with CWE-787, which describes out-of-bounds write operations that can corrupt program execution. The technical implementation involves the function failing to properly validate the length of the second argument parameter, allowing attackers to supply data exceeding the allocated buffer space. When the library attempts to process this oversized argument, it overflows the designated memory buffer and causes the segmentation fault that terminates the application process.
The operational impact of CVE-2018-20304 extends beyond simple service disruption as it provides attackers with a reliable method for causing denial of service against systems utilizing libexcel for spreadsheet processing. Applications that parse or generate excel files through this library become vulnerable to remote exploitation, particularly those that accept user input for worksheet names or other string parameters. The vulnerability affects any software that employs libexcel's workbook.c functionality, including but not limited to reporting systems, data processing applications, and spreadsheet manipulation tools. In environments where these applications are critical to business operations, such as financial systems or data analysis platforms, this vulnerability could result in significant operational downtime and potential data processing failures.
Mitigation strategies for CVE-2018-20304 should focus on immediate patching of the libexcel library to address the buffer overflow condition through proper input validation and bounds checking. Organizations should implement input sanitization measures that enforce maximum length constraints on all parameters passed to wbook_addworksheet and similar functions within the library. Network segmentation and application firewalls can help limit the attack surface by preventing unauthorized access to systems that process external spreadsheet data. Additionally, implementing robust error handling and graceful degradation mechanisms within applications using libexcel can help prevent complete service termination when malformed input is encountered. The ATT&CK framework categorizes this vulnerability under T1499.004 for network denial of service and T1550.002 for application access tokens, though the primary threat vector remains the direct exploitation of the buffer overflow condition through crafted input data. Regular security assessments and dependency updates should be prioritized to prevent similar vulnerabilities in third-party libraries that form critical components of enterprise software ecosystems.