What Security Risks Does Using Python\'s `eval()` on Untrusted Strings Present?

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

Question:

When evaluating untrusted Python strings using eval(), what are the potential security risks? Can it compromise external user data or access sensitive system features through classes, built-ins, or other means?

Answer:

Danger of Using eval() Indiscriminately

eval() is a powerful tool, but it should not be used indiscriminately. Evaluating untrusted strings can create numerous security vulnerabilities.

Risks of Using eval() with Objects:

• Reaching Sensitive System Features: If you evaluate a string using a custom dictionary containing an instance of a class, the class may provide access to sensitive system features such as os or sys.

Risks of Using eval() without Custom Dictionaries:

• Exploiting Built-ins: Built-ins like len and list can be used to perform malicious operations, even without custom dictionaries. This limits the scope of unsafe operations but still poses a risk.

Avoiding Built-in Exposure:

• Manual Evaluation: Manually parse and execute the string to prevent unexpected behavior. However, this approach is tedious and error-prone.

Alternative Options:

• Consider Alternative Approaches: Determine if there are other ways to handle user input without using eval(). Consider using a parser or specific language features that limit potential vulnerabilities.

Warning:

As highlighted by Python developers, ensuring the secure use of eval() is extremely challenging. It requires careful consideration, patching the interpreter, and understanding the potential risks. Only use eval() when absolutely necessary and take appropriate precautions to mitigate potential threats.

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