That One Silly Python Feature Hackers Love (and Devs Hate) đŸđŸ’»

Python is an amazing language. It’s clean, elegant, and super beginner-friendly.


until you stumble across one of its cursed features and realize “oh no, this is how hackers get RCE.”

Today’s silly Python feature: 👉 You can import literally anything, from anywhere.

Wait
 I Can Do That?

Normally in Python, you import modules at the top like a responsible developer:

import os
os.system("ls")

But what if I told you
 you can just conjure up imports on the fly, without ever writing import at the top?

Yep. Python lets you do this:

os = __import__("os")
os.system("echo hello, world")

Boom. No import os in sight, but suddenly you’ve got os and all its goodies.

This is silly and fun
 until you realize it’s also nightmare fuel if your server is evaluating untrusted input.

Enter the MRO Black Magic đŸ§™â€â™‚ïž

Python has something called the Method Resolution Order (MRO). It’s basically the order Python looks through classes to find methods/attributes.

Hackers realized: “Wait
 if everything in Python is an object
 and objects know their classes
 and classes know their base classes
 can’t we
 uh
 walk through this graph until we find __subclasses__ and then pull imports out of thin air?”

Yes. Yes, you can.

Something like this (simplified for the memes):

().__class__.__base__.__subclasses__()

That one-liner is like the Konami code for Python internals. From there, attackers can dig up file handles, os, sys, subprocess
 whatever they need.

Why Hackers Love This

If you’ve ever played with:

  • SSTI (Server-Side Template Injection) in Flask/Jinja2
  • RCE (Remote Code Execution) on a misconfigured Python service


then you’ve probably seen this trick in action.

You think you’ve locked down Python? Nah. Some hacker just did ().__class__.__base__.__subclasses__()[1337] and spawned a shell on your server.

But Why Is This a Problem?

Because developers sometimes write innocent-looking server code like this:

@app.route("/calc")
def calc():
    return str(eval(request.args.get("expr")))

And then wonder why their logs suddenly say:

$ curl "http://example.com/calc?expr=__import__('os').system('rm -rf /')"

😬

The Actual Pro Tip

If you’re building anything in Python that runs on the internet:

  • đŸš« Never eval() user input. Ever.
  • đŸš« Never trust template engines to “sanitize for you.”
  • ✅ Sanitize, whitelist, and validate everything.
  • ✅ Assume hackers will try __import__() from inside your app.

Final Thoughts

Python is wonderful
 but also cursed. The fact that you can import modules without importing them is equal parts genius and dangerous.

So next time you’re writing a Flask app and think: “It’s just a tiny eval, what’s the worst that could happen?” — remember: somewhere out there, a hacker is already typing:

__import__('os').system('cat /etc/passwd')


and you just turned your server into their personal playground. 🎱

👉 TL;DR: Python imports are silly, MRO is hacker magic, and you should sanitize your server code before someone “imports chaos.”