CVE-2018-18586 in libmspack
Summary
by MITRE
** DISPUTED ** chmextract.c in the chmextract sample program, as distributed with libmspack before 0.8alpha, does not protect against absolute/relative pathnames in CHM files, leading to Directory Traversal. NOTE: the vendor disputes that this is a libmspack vulnerability, because chmextract.c was only intended as a source-code example, not a supported application.
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability identified as CVE-2018-18586 resides within the chmextract.c sample program distributed with libmspack versions prior to 0.8alpha, representing a directory traversal issue that stems from inadequate handling of pathnames within Compiled HTML (CHM) files. This flaw specifically affects the chmextract utility which was intended solely as a demonstration of how to use the libmspack library rather than as a production-ready application. The core technical issue manifests when the sample program processes CHM archives containing absolute or relative pathnames that could potentially escape the intended extraction directory, allowing attackers to write files outside of the designated target location. This vulnerability falls under the category of CWE-22 - Improper Limitation of a Pathname to a Restricted Directory, which is a well-documented weakness in software systems where input validation fails to properly restrict file system access paths. The operational impact of this vulnerability extends beyond the immediate scope of the sample program, as it demonstrates a fundamental security gap in how CHM file contents are processed, particularly when dealing with maliciously crafted archives that may contain path traversal sequences. Attackers could exploit this weakness to overwrite critical system files, inject malicious content into unexpected locations, or potentially execute arbitrary code by placing payloads in privileged directories. The vendor's stance that this is not a libmspack vulnerability because chmextract.c was merely a code example does not diminish the practical security implications, as the flaw exists within the library's sample code that could be directly used or modified by developers. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1059.007 - Command and Scripting Interpreter: Python, where attackers may leverage path traversal vulnerabilities to execute malicious code through compromised file extraction processes. The issue is particularly concerning because CHM files are commonly used in software documentation and help systems, making them a frequent target for exploitation in various attack scenarios. The vulnerability's existence in a sample program underscores the importance of treating all code components with security scrutiny, regardless of their intended purpose or documentation status. Security practitioners should recognize that even example code can serve as a foundation for real-world attacks and must be evaluated for potential security flaws. The lack of proper path validation in the chmextract.c implementation creates a dangerous precedent where developers might assume that the sample code provides adequate security measures for production use, when in reality it exposes systems to directory traversal attacks through malformed CHM file contents. This vulnerability demonstrates the critical importance of implementing robust input validation and path sanitization measures, particularly when dealing with file system operations that process untrusted data sources. The incident highlights the need for comprehensive security testing of all components within software libraries, including sample applications and code examples that may be inadvertently adopted by developers without proper security review. Organizations should consider the broader implications of this vulnerability when evaluating libmspack usage, recognizing that the sample code's security flaws could potentially be replicated in custom implementations that draw upon the same code patterns. The vulnerability serves as a reminder that security must be considered throughout the entire software development lifecycle, from initial code creation to final deployment, and that even documentation examples require security validation to prevent exploitation.