CVE-2020-15801 Overview
CVE-2020-15801 is a critical vulnerability in Python 3.8.4 where sys.path restrictions specified in a python38._pth file are ignored, allowing code to be loaded from arbitrary locations. This represents an Untrusted Search Path vulnerability (CWE-426) that undermines the security controls designed to restrict module loading paths in embedded Python deployments.
The ._pth files in Python on Windows are designed to provide isolation for embedded Python installations by explicitly defining allowed import paths. When these restrictions are bypassed, an attacker can potentially load malicious Python modules from untrusted locations, leading to arbitrary code execution with the privileges of the Python process.
Critical Impact
Attackers can bypass sys.path restrictions to load malicious code from arbitrary locations, potentially achieving remote code execution on affected systems running Python 3.8.4 on Windows.
Affected Products
- Python 3.8.4 on Windows
- Microsoft Windows (as the affected platform)
- NetApp MAX Data
Discovery Timeline
- 2020-07-17 - CVE-2020-15801 published to NVD
- 2024-11-21 - Last updated in NVD database
Technical Details for CVE-2020-15801
Vulnerability Analysis
This vulnerability stems from improper handling of the python38._pth configuration file in Python 3.8.4 on Windows systems. The ._pth file mechanism was introduced to allow Python to be embedded in applications while maintaining strict control over which directories Python can import modules from. By specifying explicit paths in this file, administrators can create isolated Python environments that cannot load code from unexpected locations.
In Python 3.8.4, the path restrictions defined in the python38._pth file are not properly enforced. This means that even when administrators have carefully configured path restrictions to limit where Python can load modules from, attackers can circumvent these controls. The standard python._pth file (the executable-name variant) is not affected by this issue.
The vulnerability allows for arbitrary code loading, which can be exploited to achieve code execution. An attacker who can place a malicious Python module in a location that would normally be excluded by the ._pth restrictions can have that code executed when Python imports modules.
Root Cause
The root cause is an Untrusted Search Path vulnerability (CWE-426) where the Python interpreter fails to properly respect the path restrictions configured in the python38._pth file. This represents a regression or implementation flaw in how Python 3.8.4 processes this specific configuration file variant.
The issue lies in the initialization code that processes ._pth files during Python startup. While the restrictions from the executable-name based ._pth file (e.g., python._pth) are correctly applied, the version-specific python38._pth file's restrictions are ignored, leaving a security gap.
Attack Vector
The attack vector is network-based according to the CVSS assessment, indicating that exploitation can potentially occur remotely without requiring local access to the target system. This could manifest in scenarios where:
- An attacker can place files in directories accessible to the Python process
- The Python application processes untrusted input that influences module loading
- Network-accessible file shares or directories exist that Python can access
For exploitation, an attacker would need to place a malicious Python module in a location that Python can access but which should have been excluded by the ._pth restrictions. When the Python application subsequently imports modules, the malicious code could be loaded and executed.
The vulnerability specifically affects Windows deployments where the python38._pth file is used to restrict import paths. See the Python Issue #41304 for detailed technical discussion and the GitHub PR #21495 for the fix implementation.
Detection Methods for CVE-2020-15801
Indicators of Compromise
- Unexpected Python modules appearing in non-standard directories accessible to the Python process
- Python processes loading DLLs or .py/.pyc files from directories that should be excluded by ._pth restrictions
- Anomalous network connections or process spawning from Python 3.8.4 processes
- Modified or newly created files in directories within Python's accessible paths
Detection Strategies
- Monitor Python process execution for module loading from unexpected directories
- Audit file system access patterns of Python 3.8.4 processes on Windows systems
- Implement application whitelisting to detect unauthorized code loading
- Review Python import logs and trace module loading paths during application startup
Monitoring Recommendations
- Deploy endpoint detection solutions to monitor Python process behavior and module loading patterns
- Configure file integrity monitoring on directories that should be restricted by ._pth files
- Establish baseline behavior for Python applications and alert on deviations
- Monitor for creation of new .py, .pyc, or .pyd files in unexpected locations
How to Mitigate CVE-2020-15801
Immediate Actions Required
- Upgrade Python to version 3.8.5 or later where the vulnerability has been patched
- Audit all Python 3.8.4 installations on Windows systems within your environment
- Review and restrict file system permissions on directories accessible to Python processes
- Consider using the python._pth file format instead of python38._pth as a temporary workaround
Patch Information
The Python development team addressed this vulnerability in subsequent releases. The fix is tracked in GitHub PR #21495, which corrects the handling of version-specific ._pth files.
Organizations should upgrade to Python 3.8.5 or later to receive the security fix. For environments using NetApp MAX Data, consult the NetApp Security Advisory for vendor-specific guidance.
For detailed information about the vulnerability and patch, reference:
Workarounds
- Use the python._pth (executable-name variant) file instead of python38._pth for path restrictions, as this format is not affected
- Implement strict file system permissions to prevent unauthorized file creation in directories accessible to Python
- Deploy application control solutions to prevent execution of unauthorized Python modules
- Consider running Python applications in isolated environments such as containers with restricted file system access
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
