CVE-2014-2667 in Python
Summary
by MITRE
Race condition in the _get_masked_mode function in Lib/os.py in Python 3.2 through 3.5, when exist_ok is set to true and multiple threads are used, might allow local users to bypass intended file permissions by leveraging a separate application vulnerability before the umask has been set to the expected value.
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Analysis
by VulDB Data Team • 06/16/2021
The vulnerability identified as CVE-2014-2667 represents a significant race condition within Python's standard library implementation that affects versions 3.2 through 3.5. This flaw exists in the _get_masked_mode function located in Lib/os.py and specifically manifests when the exist_ok parameter is set to true in concurrent multi-threaded environments. The race condition occurs during the file creation process where multiple threads attempt to create the same file simultaneously, creating a window of opportunity for privilege escalation attacks. The vulnerability is particularly concerning because it leverages the fundamental behavior of umask operations and file permission handling within the operating system.
The technical implementation of this vulnerability stems from how Python handles file mode masking during concurrent file creation operations. When exist_ok=True is specified, the function attempts to create a file while simultaneously checking for its existence, but this process lacks proper synchronization mechanisms. The race condition emerges because the umask value is not consistently applied across all threads before the file permission check occurs, allowing malicious actors to exploit the temporal gap between when the file is initially checked for existence and when the proper umask is applied. This timing discrepancy creates a window where file permissions can be manipulated or bypassed, potentially allowing local users to gain unauthorized access to resources they should not have access to. The flaw is categorized under CWE-362, which specifically addresses race conditions in software implementations, making it a classic example of concurrent programming vulnerabilities.
The operational impact of CVE-2014-2667 extends beyond simple permission bypasses and can lead to serious security implications in multi-threaded applications. Attackers can exploit this vulnerability to create files with unintended permissions, potentially leading to privilege escalation scenarios where malicious code can be executed with elevated privileges. The vulnerability particularly affects applications that rely heavily on concurrent file operations and may be exploited in scenarios where multiple threads are creating files with specific permission requirements. Security professionals should note that this vulnerability aligns with ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation', as the race condition can be leveraged to gain elevated system privileges. The vulnerability also intersects with T1548.001, 'Abuse Elevation Control Mechanism', since it allows bypassing intended file permission controls through race condition exploitation.
Mitigation strategies for CVE-2014-2667 require immediate attention from system administrators and developers who maintain Python applications. The primary and most effective solution is to upgrade to Python versions 3.6 or later where this race condition has been properly addressed through improved thread synchronization mechanisms. Organizations should implement comprehensive patch management procedures to ensure all affected systems are updated promptly. Additionally, developers should avoid using exist_ok=True parameter in multi-threaded environments when file permissions are critical to application security. Alternative approaches such as implementing proper file locking mechanisms or using atomic file creation operations can help prevent exploitation of this vulnerability. Security monitoring should include detection of unusual file creation patterns that might indicate exploitation attempts, particularly in environments where multiple threads are creating files simultaneously. The vulnerability also underscores the importance of proper concurrency control in software development practices and highlights the need for thorough testing of multi-threaded applications to identify similar race conditions.