CVE-2015-5652 in Python
Summary
by MITRE
Untrusted search path vulnerability in python.exe in Python through 3.5.0 on Windows allows local users to gain privileges via a Trojan horse readline.pyd file in the current working directory. NOTE: the vendor says "It was determined that this is a longtime behavior of Python that cannot really be altered at this point."
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Analysis
by VulDB Data Team • 06/20/2022
The vulnerability identified as CVE-2015-5652 represents a classic untrusted search path issue affecting Python versions through 3.5.0 on Windows operating systems. This flaw stems from Python's executable behavior when loading dynamic link libraries, specifically the readline.pyd module that is part of the standard library. The vulnerability manifests when Python.exe executes in a directory containing a maliciously crafted readline.pyd file, which the system will load instead of the legitimate library from the Python installation directory. This behavior creates a privilege escalation vector for local attackers who can place malicious code in the current working directory and execute it with the privileges of the Python process. The issue falls under CWE-427 Uncontrolled Search Path Element, which specifically addresses the risk of loading unintended modules from untrusted locations in the search path.
The operational impact of this vulnerability extends beyond simple code execution, as it enables local privilege escalation attacks that can potentially allow attackers to execute arbitrary code with elevated privileges. When Python processes attempt to load the readline module for command-line interface functionality, the system searches for the required .pyd file in the current working directory before checking the standard Python installation paths. This search order vulnerability allows attackers to place a malicious readline.pyd file in the directory where a Python script is executed, causing the malicious code to be loaded and executed instead of the legitimate library. The vulnerability affects all Windows versions of Python through 3.5.0 and represents a fundamental design flaw in how the Python interpreter handles dynamic module loading on Windows platforms.
Security practitioners should understand that this vulnerability operates under the ATT&CK framework's privilege escalation techniques, specifically targeting the "Modify Registry" and "Execution" phases where attackers can manipulate system behavior through library loading mechanisms. The vendor's statement regarding this being a "longtime behavior that cannot really be altered" indicates that the fundamental architecture of Python's Windows module loading system was not designed with security considerations for search path resolution. This limitation means that the vulnerability cannot be easily patched without potentially breaking existing functionality, as it represents a core aspect of how Python operates on Windows systems. Organizations should consider implementing strict directory permissions, monitoring for unauthorized file modifications, and employing application whitelisting solutions to prevent exploitation of this vulnerability.
The mitigation strategies for CVE-2015-5652 should focus on operational security controls rather than code-level fixes, as the underlying behavior cannot be easily changed. System administrators should ensure that Python executables are run from secure directories with appropriate permissions, and that the current working directory is not writable by untrusted users. Additionally, implementing security awareness training for developers to avoid executing Python scripts from untrusted directories can help reduce exposure. Organizations should also consider using Python virtual environments and restricting the execution of Python scripts from user directories. The vulnerability demonstrates the importance of understanding how different operating systems handle module loading and search paths, as similar issues can affect other interpreted languages and applications that rely on dynamic library loading mechanisms.