CVE-2008-5983 in Python
Summary
by MITRE
Untrusted search path vulnerability in the PySys_SetArgv API function in Python 2.6 and earlier, and possibly later versions, prepends an empty string to sys.path when the argv[0] argument does not contain a path separator, which might allow local users to execute arbitrary code via a Trojan horse Python file in the current working directory.
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Analysis
by VulDB Data Team • 08/26/2019
The vulnerability described in CVE-2008-5983 represents a classic untrusted search path issue that affects Python's PySys_SetArgv API function across versions 2.6 and earlier, with potential impacts extending to later releases. This flaw resides in how Python processes command line arguments during initialization, specifically when handling the argv[0] parameter that contains the script name. The vulnerability manifests when the first argument lacks a path separator character, causing Python to prepend an empty string to the sys.path list. This behavior creates a dangerous condition where the current working directory is placed at the beginning of Python's module search path, effectively allowing local attackers to manipulate code execution by placing malicious Python modules in directories where legitimate scripts are executed.
The technical exploitation of this vulnerability leverages the fundamental principle of Python's module resolution mechanism, where the interpreter searches for modules in the order specified by sys.path. When an empty string is prepended to sys.path, it represents the current working directory, making it the first location Python checks for imported modules. This creates a race condition scenario where an attacker can place a Trojan horse Python file with the same name as a legitimate module that a target script imports, thereby executing arbitrary code with the privileges of the user running the Python application. The vulnerability is particularly dangerous because it operates at the core level of Python's initialization process, affecting any application that uses PySys_SetArgv to set command line arguments, including embedded Python interpreters in various applications.
The operational impact of this vulnerability extends beyond simple code execution to encompass potential privilege escalation scenarios, especially in environments where Python applications run with elevated privileges or in contexts where users have write access to directories containing Python scripts. Attackers can exploit this weakness in various real-world scenarios including web applications that embed Python interpreters, system administration tools, or any application that dynamically loads Python modules based on user-provided arguments. The vulnerability is particularly concerning from a security perspective as it requires minimal privileges to exploit and can be combined with other attack vectors to create more sophisticated compromises. According to CWE classification, this vulnerability maps to CWE-427 Uncontrolled Search Path Element, which specifically addresses the issue of programs using untrusted input to modify search paths without proper validation. The ATT&CK framework would categorize this under privilege escalation techniques, specifically leveraging weaknesses in program execution and module loading processes.
Mitigation strategies for CVE-2008-5983 require a multi-layered approach that addresses both the immediate vulnerability and broader security practices. The most direct fix involves upgrading to Python versions that have patched this issue, as newer releases properly handle the argv[0] parameter without prepending empty strings to sys.path. Organizations should also implement strict input validation practices for command line arguments and avoid using PySys_SetArgv with untrusted input in applications that might be exposed to potentially malicious users. Additional defensive measures include implementing proper directory permissions, using virtual environments to isolate module loading, and employing static code analysis tools to identify applications that might be vulnerable to this type of attack. Security teams should also monitor for applications that might be using deprecated Python versions and ensure that system administrators are aware of the risks associated with running Python applications in environments where users can write to directories containing Python scripts. The vulnerability demonstrates the importance of secure coding practices in system-level APIs and the critical need for proper validation of input parameters that influence program behavior and security boundaries.