• Python exec() bypass The “path” variable is based on user input

    codewithc
    CWC Keymaster

    I have the following challenge Python exec() but since I am not a Python developer I find it hard to get around this. It’s a sample code which is used for pentesting purposes. If anyone could assist here or via PM it would be much appreciated.

    path = urllib.parse.unquote(path)
    info = "output = 'Document: {}'"
    exec(info.format(path)) 

    The “path” variable is based on user input and specifically a URL. I need to bypass the exec() function and achieve code execution.
    I am not necessarily looking for a solution but if someone could point me at the right direction that would be great.

     


    The exec() Function

    The exec() function in Python is used for the dynamic execution of Python programs which can either be a string or object code. Imagine it’s like giving Python a mini-script to run on the fly. Seems cool, right? But here’s the kicker: it’s a double-edged sword.

    The Risks: Why User Input is Scary ?

    Let’s say you want to execute a command that includes a file path, and you’re thinking of letting the user specify that path. The moment you do that, you’re opening Pandora’s Box. A malicious user can easily execute code that deletes files, steals data, or worse. It’s akin to leaving your house keys under the doormat and then being surprised when you get robbed.

    Why You Shouldn’t Bypass Security Measures ?

    You might be tempted to “sanitize” the user input and then feed it into exec(). But that’s like putting a Band-Aid on a broken dam. No matter how careful you are, there’s always a way for harmful code to sneak through. And guess what? You’re accountable for whatever havoc it wreaks.

    Alternatives to Consider ?

    Instead of using exec() with user input, consider other methods to achieve the same functionality:

    1. Limited Scopes: Use predefined scopes to limit what code can be executed.
    2. Config Files: Use configuration files to allow users to modify program behavior.
    3. Safe Evaluation: If you only need to evaluate expressions, consider using ast.literal_eval which only allows processing literals.

    In Closing

    The exec() function is powerful but not to be trifled with, especially not with user-generated data. Keep your wits about you and choose safer alternatives when crafting your Python spells. It’s better to be safe than sorry, especially when the stakes can be as high as code execution! Thanks for tuning in, and code responsibly! ?‍♂️?

  • codewithc
    CWC Keymaster

    Normally exec() function will be disable by hosting provider.

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