CVE-2011-4944 in Mac OS X
Summary
by MITRE
Python 2.6 through 3.2 creates ~/.pypirc with world-readable permissions before changing them after data has been written, which introduces a race condition that allows local users to obtain a username and password by reading this file.
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Analysis
by VulDB Data Team • 06/01/2021
The vulnerability described in CVE-2011-4944 represents a classic race condition flaw in Python's package management system that affects versions 2.6 through 3.2. This issue occurs during the creation of the .pypirc configuration file which stores authentication credentials for Python package repositories. The flaw stems from the improper handling of file permissions during the file creation process, creating a window of opportunity for local attackers to exploit.
The technical implementation of this vulnerability involves the Python package installer's approach to managing authentication credentials. When Python creates the ~/.pypirc file to store repository login information, it initially creates the file with world-readable permissions before subsequently changing these permissions to restrict access. This sequence creates a race condition where an attacker can read the file contents between the initial creation and the permission change operations. The Common Weakness Enumeration categorizes this as a weakness related to improper handling of permissions and access control, specifically CWE-276 which deals with incorrect permissions for a resource.
The operational impact of this vulnerability extends beyond simple credential theft, as it provides attackers with direct access to repository authentication information that could enable further exploitation. Local users who can access the system can read the username and password stored in the .pypirc file, potentially allowing them to publish malicious packages, modify existing packages, or perform other unauthorized actions on the repository. This vulnerability aligns with ATT&CK technique T1555.003 which covers credential access through the use of stolen credentials, and demonstrates how seemingly benign file creation operations can introduce significant security risks.
The race condition aspect of this vulnerability makes it particularly concerning as it requires no special privileges beyond local access and can be exploited repeatedly. Attackers can monitor for the creation of the .pypirc file and quickly read its contents before the permission changes take effect. The vulnerability highlights the importance of proper file handling practices and the principle of least privilege in system design. Organizations should note that this issue affects multiple Python versions and can be particularly dangerous in multi-user environments where different users share the same system resources.
Mitigation strategies for this vulnerability include immediate patching of affected Python versions, implementing proper file permission handling during creation, and monitoring for unauthorized access to configuration files. System administrators should also consider implementing additional security controls such as file integrity monitoring and access logging to detect potential exploitation attempts. The fix typically involves modifying the file creation process to set appropriate permissions immediately upon creation rather than relying on subsequent permission changes, thereby eliminating the race condition window that attackers exploit. This vulnerability serves as a reminder of the critical importance of proper file permission management and the potential security implications of seemingly simple file operations in software systems.