Is Using Python\'s `eval()` Function with Untrusted Strings Secure?

Evaluating Untrusted Strings with Python's eval() Function: Security Considerations

Evaluating untrusted strings using Python's eval() function poses significant security risks that require careful consideration. Let's examine specific scenarios and explore potential vulnerabilities:

1. eval(string, {"f": Foo()}, {}):

This scenario involves a custom dictionary containing an instance of a class named Foo. While it may seem harmless, this can potentially allow an attacker to reach sensitive system components such as os or sys if the Foo class provides access to them.

2. eval(string, {}, {}):

Using only built-in functions and objects in the evaluation context (via an empty dictionary) may appear safer. However, certain built-in functionality, such as len and list, can be abused by malicious input to lead to resource exhaustion attacks.

3. Removing Built-ins from Eval Context:

It is currently not possible to completely remove built-ins from the evaluation context without significant modifications to the Python interpreter. This makes it challenging to ensure a secure environment for untrusted string evaluation.

Precautions and Alternatives:

Given the inherent risks associated with eval(), it is strongly recommended to avoid its use in production code. If it is necessary, consider the following precautions:

• Use trusted input sources and validate the strings before evaluation.
• Limit the scope of the evaluation by using restricted execution environments (e.g., subprocess with shell=False).
• Implement a custom sandbox to enforce access restrictions.

For alternative methods of data transfer, consider using JSON-like formats or dedicated data exchange protocols that provide built-in security measures.

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