CVE-2017-6419 in libmspack
Summary
by MITRE
mspack/lzxd.c in libmspack 0.5alpha, as used in ClamAV 0.99.2, allows remote attackers to cause a denial of service (heap-based buffer overflow and application crash) or possibly have unspecified other impact via a crafted CHM file.
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Analysis
by VulDB Data Team • 12/15/2022
The vulnerability identified as CVE-2017-6419 represents a critical heap-based buffer overflow within the mspack library component known as lzxd.c, which is part of libmspack version 0.5alpha. This flaw specifically affects ClamAV 0.99.2 and other software implementations that utilize this library for processing CHM (Compiled HTML Help) files. The vulnerability stems from inadequate input validation and boundary checking during the decompression process of malformed CHM archives, creating a scenario where maliciously crafted file structures can trigger memory corruption. The affected library is commonly integrated into antivirus and security scanning software due to its role in handling Microsoft's proprietary CHM file format, which is widely used for documentation and help systems across Windows platforms. This integration makes the vulnerability particularly dangerous as it can be exploited through standard file scanning operations that antivirus software performs on user systems.
The technical nature of this vulnerability places it squarely within the realm of heap-based buffer overflow conditions, which are classified under CWE-121 as heap-based buffer overflow. The flaw occurs during the decompression of CHM files where the lzxd.c component fails to properly validate the size parameters of compressed data structures before allocating memory buffers. When a maliciously crafted CHM file is processed, the attacker can manipulate the compression headers to specify buffer sizes that exceed allocated memory boundaries, causing memory corruption that manifests as application crashes or potentially more severe consequences. The vulnerability operates at the intersection of memory management and decompression algorithms, where improper bounds checking allows attackers to overwrite adjacent memory regions, potentially leading to arbitrary code execution or complete application termination. This type of vulnerability is particularly insidious because it can be triggered through routine file processing without requiring user interaction beyond the mere act of scanning a malicious file.
The operational impact of CVE-2017-6419 extends far beyond simple denial of service, as it represents a significant threat to security infrastructure. When exploited, this vulnerability can cause security applications like ClamAV to crash during routine scanning operations, effectively rendering the antivirus solution temporarily ineffective against other threats during the restart period. Organizations relying on ClamAV for malware detection and prevention face potential exposure to attacks that could bypass security measures while the application is recovering from the crash. The vulnerability's potential for unspecified other impacts suggests that under certain conditions, attackers might be able to achieve more sophisticated exploitation techniques beyond simple application termination. This is particularly concerning in enterprise environments where ClamAV is deployed as part of comprehensive security solutions, as the disruption could cascade through entire network security infrastructures, potentially leading to extended periods of reduced threat detection capability.
Mitigation strategies for CVE-2017-6419 must address both immediate remediation and long-term architectural improvements to prevent similar vulnerabilities from emerging. The primary solution involves updating to patched versions of libmspack and ClamAV, specifically targeting versions that include proper input validation and boundary checking mechanisms. System administrators should prioritize patching across all environments where ClamAV or similar software is deployed, particularly in high-value targets such as email servers, file servers, and endpoint security solutions. Additionally, implementing file type filtering and sandboxing techniques can provide defense-in-depth measures that limit the potential impact of such vulnerabilities by preventing untrusted CHM files from being processed by security applications. Organizations should also consider implementing network-based detection mechanisms that can identify and block suspicious CHM file transfers, as well as establishing monitoring procedures to detect application crashes or unusual behavior that might indicate exploitation attempts. The vulnerability highlights the importance of comprehensive input validation and memory safety practices in security software development, aligning with ATT&CK technique T1059.007 for Command and Scripting Interpreter and T1499.004 for Endpoint Denial of Service, which emphasize the need for robust defenses against memory corruption vulnerabilities that can be leveraged for system compromise.