CVE-2018-20213 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 name. NOTE: this is not a Microsoft product.
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Analysis
by VulDB Data Team • 04/21/2020
The vulnerability identified as CVE-2018-20213 resides within the libexcel library's workbook.c component, specifically in the wbook_addworksheet function which is part of the libexcel 0.01 release. This flaw represents a classic buffer overflow condition that manifests when processing worksheet names exceeding normal parameter limits. The affected library is a third-party parsing library designed for handling excel spreadsheet files and is not associated with any microsoft products. The vulnerability occurs during the parsing of worksheet names where the application fails to properly validate the length of input strings before processing them, creating a scenario where maliciously crafted input can trigger unexpected program behavior.
The technical exploitation of this vulnerability leverages a simple yet effective approach where an attacker provides an excessively long worksheet name to the wbook_addworksheet function. When the library attempts to process this oversized name, it fails to implement proper bounds checking or length validation, leading to a segmentation fault that ultimately results in a denial of service condition. This type of vulnerability falls under the CWE-121 category of stack-based buffer overflow, where insufficient bounds checking allows memory corruption to occur during string processing operations. The vulnerability demonstrates poor input validation practices and highlights the critical importance of implementing proper parameter validation in parsing libraries that handle user-supplied data.
The operational impact of CVE-2018-20213 extends beyond simple service disruption as it can be leveraged by attackers to create persistent denial of service conditions within applications that rely on libexcel for spreadsheet processing. Systems utilizing this library for automated spreadsheet parsing, data import operations, or file validation processes become vulnerable to exploitation, potentially affecting business continuity and operational efficiency. The vulnerability is particularly concerning in environments where automated processing of user-uploaded files occurs, as attackers can craft malicious spreadsheet files that will cause service interruptions when processed by vulnerable applications. This vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks and demonstrates how seemingly benign input validation flaws can be weaponized for service disruption.
Mitigation strategies for this vulnerability should focus on immediate library updates or patches provided by the maintainers of libexcel, as the most effective solution involves addressing the root cause through proper bounds checking implementation. Organizations should implement input validation measures that enforce reasonable limits on worksheet name lengths and incorporate defensive programming practices such as using safe string handling functions. Additionally, deploying intrusion detection systems that can identify suspicious file processing patterns and implementing proper application sandboxing can help reduce the impact of exploitation attempts. The vulnerability serves as a reminder of the critical importance of thorough input validation in parsing libraries and demonstrates how simple parameter validation flaws can have significant operational consequences in enterprise environments relying on third-party data processing components.