CVE-2026-2297 in CPython
Summary
by MITRE • 03/05/2026
The import hook in CPython that handles legacy *.pyc files (SourcelessFileLoader) is incorrectly handled in FileLoader (a base class) and so does not use io.open_code() to read the .pyc files. sys.audit handlers for this audit event therefore do not fire.
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Analysis
by VulDB Data Team • 06/24/2026
The vulnerability described in CVE-2026-2297 represents a critical security flaw within the Python interpreter's module loading mechanism that undermines audit capabilities and potentially exposes systems to unauthorized code execution. This issue specifically targets the interaction between CPython's import system and its audit hook infrastructure, creating a scenario where security monitoring mechanisms fail to detect malicious activity during module loading operations. The flaw exists in the legacy *.pyc file handling process, which is a fundamental component of Python's runtime environment and is utilized across countless applications and systems worldwide.
The technical root cause of this vulnerability lies in the improper implementation of the SourcelessFileLoader class within CPython's import system. When Python encounters legacy .pyc files during module loading, the system should utilize io.open_code() to properly handle these files, ensuring that audit events are correctly triggered and monitored. However, the current implementation fails to invoke this critical function, causing the system to bypass the audit hook infrastructure entirely. This misimplementation creates a direct pathway for malicious actors to execute code without proper security monitoring, as the sys.audit handlers that should be triggered during file loading operations remain inactive. The flaw affects the FileLoader base class and its interaction with the SourcelessFileLoader, creating a gap in the interpreter's security controls that directly violates standard security practices.
The operational impact of this vulnerability extends far beyond simple code execution concerns, as it fundamentally compromises the security monitoring capabilities of Python applications. When sys.audit handlers fail to fire during .pyc file loading, organizations lose visibility into potentially malicious code injection attempts that occur during the module import process. This creates a significant blind spot in security operations, particularly in environments where audit logging is critical for compliance and threat detection. The vulnerability affects the core Python runtime functionality, meaning that any application relying on legacy .pyc files for module loading becomes susceptible to undetected malicious activity. This flaw can be exploited by attackers to bypass security controls, potentially leading to data breaches, privilege escalation, or complete system compromise. The impact is particularly severe given that .pyc files are widely used throughout Python ecosystems for performance optimization and deployment scenarios.
Security mitigations for this vulnerability require immediate attention and systematic remediation across affected Python installations. The primary solution involves updating to a patched version of CPython that correctly implements io.open_code() usage during .pyc file loading operations, ensuring that audit handlers fire as expected. Organizations should also implement comprehensive monitoring of module loading activities and consider additional security controls such as file integrity checking, runtime application control, and enhanced audit logging. The vulnerability aligns with CWE-254 and CWE-353 categories related to security weaknesses in input handling and improper file access control, while also mapping to ATT&CK techniques such as T1059 for execution and T1566 for social engineering through code injection. System administrators should prioritize patching efforts and conduct thorough security assessments to identify any potential exploitation attempts that may have occurred due to this vulnerability, particularly focusing on anomalous module loading patterns that could indicate malicious activity.