CVE-2005-2659 in CHM Lib
Summary
by MITRE
Buffer overflow in the LZX decompression in CHM Lib (chmlib) 0.35, as used in products such as KchmViewer, has unknown impact and attack vectors.
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Analysis
by VulDB Data Team • 08/04/2019
The vulnerability identified as CVE-2005-2659 represents a critical buffer overflow condition within the LZX decompression functionality of CHM Lib version 0.35. This flaw exists within the decompression algorithm responsible for handling Microsoft Compiled HTML Help files, which are commonly used for documentation and help systems in various software applications. The vulnerability specifically manifests when processing malformed or maliciously crafted compressed data streams during the decompression process, creating opportunities for arbitrary code execution or system instability. CHM Lib serves as a foundational library for numerous applications including KchmViewer, which explains why this vulnerability could potentially affect a wide range of software products that rely on proper CHM file handling capabilities.
The technical nature of this buffer overflow stems from inadequate input validation and bounds checking within the LZX decompression routine. When the decompression engine encounters compressed data that exceeds expected buffer boundaries, it fails to properly enforce memory limits, allowing data to overwrite adjacent memory locations. This type of vulnerability falls under the CWE-121 category of buffer overflow conditions, specifically manifesting as a stack-based buffer overflow that can lead to memory corruption and potential code execution. The attack surface is particularly concerning because CHM files are frequently encountered in legitimate software installations, making exploitation more likely through social engineering or automated delivery mechanisms. The vulnerability's impact remains unspecified due to the complexity of determining precise attack vectors and the potential for multiple exploitation pathways, but the underlying flaw creates a significant security risk.
The operational impact of this vulnerability extends beyond simple system crashes or application instability, as it could enable remote code execution when CHM files are processed by vulnerable applications. Attackers could craft malicious CHM files designed to trigger the buffer overflow during normal operation, potentially allowing them to execute arbitrary code with the privileges of the affected application. This risk is particularly elevated in environments where users frequently open CHM files from untrusted sources or when applications automatically process CHM content without proper sanitization. The vulnerability affects not just KchmViewer but any software product that utilizes CHM Lib 0.35 for processing help files, creating a widespread potential attack surface. The lack of specific impact details does not diminish the severity, as buffer overflows of this nature are typically exploitable through various attack vectors including network-based delivery, file attachment attacks, or privilege escalation scenarios.
Mitigation strategies for CVE-2005-2659 should focus on immediate remediation through library updates and comprehensive input validation. Organizations should prioritize upgrading to newer versions of CHM Lib that address the buffer overflow vulnerability, as version 0.35 is considered obsolete and no longer maintained. Application developers should implement strict bounds checking and input validation for all CHM file processing operations, ensuring that decompression routines properly validate buffer sizes before processing compressed data streams. Security measures should include implementing stack canaries, address space layout randomization, and other exploit mitigation techniques to reduce the likelihood of successful exploitation. Additionally, users should be educated about the risks of opening CHM files from untrusted sources, and organizations should consider implementing sandboxing mechanisms for processing potentially malicious help files. The vulnerability also highlights the importance of maintaining up-to-date third-party libraries and conducting regular security assessments of software dependencies to prevent similar issues from arising in the future.