CVE-2008-5299 in chm2pdf
Summary
by MITRE
chm2pdf 0.9 allows user-assisted local users to delete arbitrary files via a symlink attack on .chm files in the (1) /tmp/chm2pdf/work or (2) /tmp/chm2pdf/orig temporary directories.
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Analysis
by VulDB Data Team • 02/03/2025
The vulnerability identified as CVE-2008-5299 affects chm2pdf version 0.9, a utility designed to convert CHM (Compiled HTML Help) files into PDF format. This flaw represents a significant security weakness that enables local attackers to perform unauthorized file deletion operations through a carefully crafted symlink attack against temporary directories used by the application. The vulnerability specifically targets two temporary directories: /tmp/chm2pdf/work and /tmp/chm2pdf/orig, which are utilized during the conversion process to store intermediate files and temporary data. The issue stems from insufficient validation of symbolic links and inadequate handling of temporary file creation processes, creating an attack vector that can be exploited by malicious users with local access to the system.
The technical implementation of this vulnerability involves a classic race condition and symlink attack scenario. When chm2pdf processes CHM files, it creates temporary files in the designated directories without proper security checks for existing symbolic links. An attacker can exploit this by pre-creating symbolic links in either of the temporary directories that point to sensitive files on the system. When the application attempts to create temporary files with the same names as the symbolic links, the system automatically follows the links and writes data to the target files, potentially leading to their deletion or modification. This type of vulnerability is categorized under CWE-367, which addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions, and represents a specific instance of insecure temporary file handling that violates fundamental security principles for file system operations. The attack requires local system access but does not require elevated privileges, making it particularly dangerous in multi-user environments where attackers might have limited access but can still cause significant damage.
The operational impact of this vulnerability extends beyond simple file deletion, as it can be leveraged to compromise system integrity and potentially facilitate further attacks. Attackers can use this weakness to overwrite critical system files, remove important configuration data, or corrupt user files, depending on the target of their symbolic links. The vulnerability affects any system running chm2pdf 0.9 where local users have the ability to create files in the temporary directories, which typically includes regular users with shell access. This creates a scenario where a compromised user account or an attacker with limited access can cause significant disruption to system operations. The vulnerability also aligns with ATT&CK technique T1059.007 for executing malicious code through command-line interfaces and T1070.006 for clearing system logs, as the exploitation can be part of a broader attack chain to hide malicious activities or maintain persistence. The lack of proper file system permissions checking and the absence of secure temporary file creation mechanisms make this vulnerability particularly challenging to detect and prevent.
Mitigation strategies for CVE-2008-5299 should focus on implementing secure temporary file handling practices and restricting access to the vulnerable directories. System administrators should immediately upgrade to a patched version of chm2pdf if available, as the vulnerability has been addressed in subsequent releases through proper symlink validation and secure temporary file creation mechanisms. The recommended approach involves ensuring that temporary directories are created with appropriate permissions and that symbolic link checks are performed before file operations. Additionally, implementing proper file system access controls and monitoring for unauthorized file creation in temporary directories can help detect potential exploitation attempts. Organizations should also consider implementing least privilege principles, restricting write access to the temporary directories, and using more secure file handling libraries that automatically handle race conditions. The vulnerability highlights the importance of following secure coding practices and adhering to standards such as the Open Web Application Security Project (OWASP) secure coding guidelines, which emphasize the need for proper input validation and secure file system operations. Regular security audits and penetration testing should include checks for similar vulnerabilities in other applications that handle temporary files, as this type of flaw is commonly found in legacy software implementations that do not follow modern security best practices.