The ` safe eval expression()` function in the computed fields feature uses an AST (Abstract Syntax Tree) validator that only blocks attributes starting with an underscore. Because Python generator and frame object attributes such as `gi frame`, `f back`, and `f builtins` do not start with an underscore, they can be used to escape the sandbox and achieve arbitrary code execution. An unauthenticated attacker can trigger this by sending a 'POST /crawl' request with a crafted `JsonCssExtractionStrategy` schema containing a malicious computed field expression. This allows the attacker to access the frame chain, reach `f builtins` to import the `os` module, and execute arbitrary system commands inside the Docker container, potentially leading to file system access and secret exfiltration.