CVE-2018-14682 in libmspack
Summary
by MITRE
An issue was discovered in mspack/chmd.c in libmspack before 0.7alpha. There is an off-by-one error in the TOLOWER() macro for CHM decompression.
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Analysis
by VulDB Data Team • 04/27/2023
The vulnerability identified as CVE-2018-14682 represents a critical memory safety issue within the libmspack library, specifically affecting the mspack/chmd.c component. This flaw exists in versions prior to 0.7alpha and stems from an off-by-one error within the TOLOWER() macro implementation during CHM (Microsoft Compiled HTML Help) file decompression operations. The issue manifests when processing malformed CHM files that trigger the vulnerable code path, creating potential for memory corruption and arbitrary code execution. The vulnerability affects systems that utilize libmspack for decompressing CHM files, which are commonly used for help documentation in various Microsoft applications and software packages.
The technical root cause of this vulnerability lies in the improper handling of character conversion within the TOLOWER() macro, where an off-by-one error occurs during the processing of character data. This error typically arises when the macro attempts to convert uppercase characters to lowercase but fails to properly account for boundary conditions in memory access patterns. During CHM decompression, the library processes compressed help files that contain embedded character data, and when malformed input triggers the vulnerable TOLOWER() macro, it can cause buffer overreads or overwrites. The flaw operates at the level of memory management and string processing, where the macro's implementation does not correctly handle the edge cases of character conversion, particularly when dealing with boundary conditions in compressed data structures.
The operational impact of CVE-2018-14682 extends beyond simple memory corruption, as it creates potential attack vectors for remote code execution when systems process untrusted CHM files. Attackers can craft malicious CHM files that, when opened by applications relying on libmspack for decompression, trigger the off-by-one error and potentially execute arbitrary code with the privileges of the affected application. This vulnerability is particularly concerning in environments where users might encounter CHM files from untrusted sources, such as email attachments, web downloads, or file sharing platforms. The flaw affects a wide range of software applications that depend on libmspack for CHM file processing, including web browsers, document viewers, and help system components. Security researchers have classified this as a memory corruption vulnerability that can be exploited through improper input handling, making it a significant concern for system administrators and security professionals managing software that processes compressed help files.
Mitigation strategies for CVE-2018-14682 primarily focus on updating to libmspack version 0.7alpha or later, where the off-by-one error in the TOLOWER() macro has been corrected. System administrators should prioritize patching affected applications that rely on libmspack for CHM file decompression, particularly those used in enterprise environments where CHM files are commonly encountered. Additional protective measures include implementing strict input validation for CHM files, using sandboxing techniques when processing untrusted documents, and deploying network-based intrusion detection systems that can identify attempts to exploit this vulnerability. Organizations should also consider disabling CHM file processing capabilities in applications where they are not essential, and implementing application whitelisting to prevent execution of potentially malicious CHM files. The vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and may map to ATT&CK techniques involving execution through malicious file formats or exploitation of memory corruption vulnerabilities. Regular security audits and vulnerability assessments should include checks for libmspack versions to ensure proper patch management and reduce the risk of exploitation.