These are some tricks to bypass python sandbox protections and execute arbitrary commands.
## Command Execution Libraries
The first thing you need to know is if you can directly execute code with some already imported library, or if you could import any of these libraries:
Remember that the _**open**_ and _**read**_ functions can be useful to **read files** inside the python sandbox and to **write some code** that you could **execute** to **bypass** the sandbox.
Python2 **input\(\)** function allows to execute python code before the program crashes.
### Importing
```python
import os
from os import *
__import__('os').system("ls")
```
If **`sys`**module is present, you can use it to access **`os`**library for example:
```python
sys.modules["os"].system("ls")
```
You can also import libraries and any file is using **`execfile()`** \(python2\):
```python
execfile('/usr/lib/python2.7/os.py')
system('ls')
```
Python try to **load libraries from the current directory first**: `python3 -c 'import sys; print(sys.path)'`
## Executing python code
This is really interesting if some characters are forbidden because you can use the **hex/octal/B64** representation to **bypass** the restriction:
In a previous example you can see how to execute any python code using the `compile` function. This is really interesting because you can execute whole scripts with loops and everything in a one liner \(and we could do the same using `exec`\).
Anyway, sometimes it could be useful to **create** a **compiled object** in a local machine and execute it in the **CTF** \(for example because we don't have the `compile` function in the CTF\).
For example, let's compile and execute manually a function that reads _./poc.py_:
If you cannot access `eval` or `exec` you could create a **proper function**, but calling it directly is usually going to fail with: _constructor not accessible in restricted mode_. So you need a **function not in the restricted environment call this function.**
](https://docs.python.org/2/library/functions.html)[Builtins functions of python3](https://docs.python.org/3/library/functions.html)
If you can access to the**`__builtins__`** object you can import libraries \(notice that you could also use here other string representation showed in last section\):
When you don't have \_\_builtins\_\_ you are not going to be able to import anything nor even read or write files. But there is a way to take that functionality back:
In some CTFs you could be provided the name of a custom function where the flag resides and you need to see the internals of the function to extract it.
`__globals__` and `func_globals`\(Same\) Obtains the global environment. In the example you can see some imported modules, some global variables and their content declared:
Notice that **if you cannot import `dis` in the python sandbox** you can obtain the **bytecode** of the function \(`get_flag.func_code.co_code`\) and **disassemble** it locally. You won't see the content of the variables being loaded \(`LOAD_CONST`\) but you can guess them from \(`get_flag.func_code.co_consts`\) because `LOAD_CONST`also tells the offset of the variable being loaded.
You can download the package to create the reverse shell here. Please, note that before using it you should **decompress it, change the `setup.py`, and put your IP for the reverse shell**:
