CVE-2008-4108 in Python
Summary
by MITRE
Tools/faqwiz/move-faqwiz.sh (aka the generic FAQ wizard moving tool) in Python 2.4.5 might allow local users to overwrite arbitrary files via a symlink attack on a tmp$RANDOM.tmp temporary file. NOTE: there may not be common usage scenarios in which tmp$RANDOM.tmp is located in an untrusted directory.
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Analysis
by VulDB Data Team • 10/08/2018
The vulnerability identified as CVE-2008-4108 resides within the Python 2.4.5 distribution's generic FAQ wizard moving tool, specifically in the move-faqwiz.sh script located in the Tools/faqwiz directory. This flaw represents a classic symlink attack vulnerability that exploits insecure temporary file handling practices. The vulnerability occurs when the script creates temporary files using the pattern tmp$RANDOM.tmp, which can be manipulated by local attackers to overwrite arbitrary files on the system. The security risk emerges from the predictable naming convention combined with the lack of proper file permission checks during temporary file creation.
This vulnerability falls under the CWE-377 weakness category, specifically CWE-377: Insecure Temporary File, which is classified as a high-severity issue in the Common Weakness Enumeration framework. The flaw allows attackers to exploit a race condition where they can create symbolic links with the expected temporary filename before the legitimate process creates the actual temporary file. This creates a scenario where the moving tool, when executed with elevated privileges or in a context where it can modify files, will write to the attacker-controlled symlink target instead of the intended temporary file location. The vulnerability is particularly concerning because it can potentially be exploited to overwrite critical system files, configuration files, or even files owned by other users.
The operational impact of this vulnerability extends beyond simple file overwriting, as it can be leveraged in broader attack scenarios within a compromised system. According to the MITRE ATT&CK framework, this vulnerability could be used as part of a privilege escalation technique under the T1068: Exploitation for Privilege Escalation tactic. The vulnerability is most dangerous when the FAQ wizard moving tool is executed with elevated privileges, as it would allow attackers to overwrite system-critical files or modify the behavior of the Python installation itself. Even in less privileged scenarios, the ability to overwrite arbitrary files in writable directories represents a significant security risk that can be combined with other vulnerabilities to achieve more severe outcomes.
The vulnerability is particularly relevant in environments where the Python tools are installed with write permissions for non-root users or when the tool is executed in directories where attackers have write access. While the original description notes that common usage scenarios might not typically place the tmp$RANDOM.tmp file in untrusted directories, this assumption can be easily violated in poorly configured systems or when tools are run in shared or temporary directories. The exploit requires local access to the system and knowledge of the specific tool being used, but once exploited, it can provide persistent access or system compromise. Effective mitigation strategies should include ensuring that temporary file creation uses secure methods such as mkstemp() or similar atomic operations that prevent symlink attacks, implementing proper file permission checks, and ensuring that tools are not run with unnecessary elevated privileges. Additionally, system administrators should audit the execution paths of such tools and ensure that they are not executed in directories with insecure permissions or where attackers can manipulate the file system structure.