A vulnerability in the asteval library used by Checkov allows attackers who can control input to bypass safety checks and execute arbitrary Python code. The flaw arises because the attribute access verification can be circumvented by modifying AST nodes at runtime, exploiting a time-of-check to time-of-use (TOCTOU) issue. Specifically, the Procedure class exposes its AST in an unprotected attribute, enabling attackers to alter the AST and access dangerous dunder methods like __getattribute__. This leads to sandbox escape and arbitrary code execution within the application's context.