CVE-2024-0397 in CPython
Summary
by MITRE • 06/17/2024
A defect was discovered in the Python “ssl” module where there is a memory race condition with the ssl.SSLContext methods “cert_store_stats()” and “get_ca_certs()”. The race condition can be triggered if the methods are called at the same time as certificates are loaded into the SSLContext, such as during the TLS handshake with a certificate directory configured. This issue is fixed in CPython 3.10.14, 3.11.9, 3.12.3, and 3.13.0a5.
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Analysis
by VulDB Data Team • 12/02/2024
The vulnerability identified as CVE-2024-0397 represents a critical memory race condition within the Python ssl module that specifically affects the ssl.SSLContext methods cert_store_stats() and get_ca_certs(). This flaw emerges from inadequate thread synchronization mechanisms when multiple threads attempt to access and modify the certificate store concurrently. The race condition occurs during the dynamic loading of certificates into the SSLContext, particularly during TLS handshakes when certificate directories are configured, creating a window where memory access conflicts can result in unpredictable behavior and potential security implications. The vulnerability stems from the fundamental design flaw where shared resources within the SSLContext certificate store are not properly protected against concurrent access patterns, making it susceptible to data corruption and inconsistent state management.
The technical implementation of this race condition manifests when multiple threads simultaneously invoke cert_store_stats() or get_ca_certs() methods while certificate loading operations are in progress. During TLS handshakes with certificate directory configurations, the ssl module maintains an internal certificate store that gets modified concurrently with method calls. This concurrent access pattern can lead to memory corruption where thread A reads from a certificate store while thread B modifies it, resulting in inconsistent data retrieval and potential buffer overflows. The flaw is particularly dangerous because it operates at the memory level, affecting the underlying certificate storage structures without explicit error handling or recovery mechanisms. This type of vulnerability maps directly to CWE-362, which describes concurrent execution using shared data structures without proper synchronization controls, and aligns with ATT&CK technique T1555.003 for credential access through manipulation of system memory.
The operational impact of CVE-2024-0397 extends beyond simple memory corruption to potentially compromise the integrity of TLS communications within Python applications. Systems utilizing Python's ssl module for secure communications may experience certificate validation failures, connection drops, or even arbitrary code execution if the memory corruption leads to code execution vulnerabilities. Applications that dynamically load certificates during runtime, particularly those implementing certificate directory monitoring or automated certificate management, face the highest risk exposure. The vulnerability affects Python versions prior to 3.10.14, 3.11.9, 3.12.3, and 3.13.0a5, making widespread deployment of affected applications vulnerable to exploitation. Network services, web applications, and any Python-based systems relying on ssl.SSLContext for secure communications represent high-value targets for attackers seeking to exploit this race condition.
Mitigation strategies for CVE-2024-0397 require immediate patching of affected Python installations to versions containing the fix. Organizations should prioritize updating their Python environments to ensure all instances of the ssl module operate with proper thread synchronization mechanisms. Additionally, system administrators should implement monitoring solutions to detect potential race condition scenarios during certificate loading operations and consider implementing application-level locking mechanisms when multiple threads interact with SSLContext methods. The fix implemented in CPython addresses the root cause by introducing proper mutex locks around certificate store access operations, ensuring that concurrent access to cert_store_stats() and get_ca_certs() methods is properly serialized. Security teams should also review their certificate management policies to minimize concurrent access patterns and implement proper certificate caching strategies to reduce the frequency of certificate store modifications during active TLS connections. The remediation process should include comprehensive testing of applications to verify that the patched ssl module operates correctly under concurrent access conditions.