secimport

A sandbox/supervisor for python modules.
Medium Article

secimport can be used to:

Confine/Restrict specific python modules inside your production environment.
- Open Source, 3rd party from unstrusted sources.
- Audit the flow of your python application at user-space/os/kernel level.
Run an entire python application under unified configuration
- Like seccomp but not limited to Linux kernels. Cross platform.

Requirements

The only requirement is a Python interpreter that was built with --with-dtrace.

See INSTALL.md for a detailed setup from scratch.
pip
- python3 -m pip install secimport
Poetry
- python3 -m pip install poetry && python3 -m poetry build

Quick Start

For the full list of examples, see EXAMPLES.md.

Python Shell Interactive Example

Python 3.10.0 (default, May  2 2022, 21:43:20) [Clang 13.0.0 (clang-1300.0.27.3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.

# Let's import subprocess module, limiting it's syscall access.
>>> import secimport
>>> subprocess = secimport.secure_import("subprocess")

# Let's import os 
>>> import os
>>> os.system("ps")
  PID TTY           TIME CMD
 2022 ttys000    0:00.61 /bin/zsh -l
50092 ttys001    0:04.66 /bin/zsh -l
75860 ttys001    0:00.13 python
0
# It worked as expected, returning exit code 0.


# Now, let's try to invoke the same logic using a different module, "subprocess", that was imported using secure_import:
>>> subprocess.check_call('ps')
[1]    75860 killed     python

# Damn! That's cool.

The dtrace profile for the module is saved under:
- /tmp/.secimport/sandbox_subprocess.d:

The log file for this module is under

/tmp/.secimport/sandbox_subprocess.log:

...

(OPENING SHELL using posix_spawn): (pid 75860) (thread 344676) (user 501) (python module: <stdin>) (probe mod=, name=entry, prov=syscall func=posix_spawn) /bin/sh 
    #posix_spawn,

(TOUCHING FILESYSTEM): write(140339021606912) from thread 344676
            libsystem_kernel.dylib`__fork+0xb
            _posixsubprocess.cpython-310-darwin.so`do_fork_exec+0x29
            _posixsubprocess.cpython-310-darwin.so`subprocess_fork_exec+0x71f
            python.exe`cfunction_call+0x86
killing...
killed.

Shell blocking

# example.py - Executes code upon import;
import os;

os.system('Hello World!');

# production.py - Your production code
from secimport import secure_import 

example = secure_import('example', allow_shells=False)

Let's run the and see what happens:

(root) sh-3.2#  export PYTHONPATH=$(pwd)/src:$(pwd)/examples:$(pwd):$PYTHONPATH
(root) sh-3.2#  python examples/production.py 
Successfully compiled dtrace profile:  /tmp/.secimport/sandbox_example.d
Killed: 9

We imported example with limited capabilities.
If a syscall like spawn/exec/fork/forkexec will be executed
- The process will be killed with -9 signal.

Network blocking

>>> import requests
>>> requests.get('https://google.com')
<Response [200]>
  

>>> from secimport import secure_import
>>> requests = secure_import('requests', allow_networking=False)

# The next call should kill the process,
# because we disallowed networking for the requests module.
>>> requests.get('https://google.com')
[1]    86664 killed

Log4Shell as an example

Not related for python, but for the sake of explanation (Equivilant Demo soon).

Log4Shell - CVE-2021-44228
- Let's say we want to block log4j from doing crazy things.
- In the following import we deny log4j from opening an LDAP connection / shell:
  - log4j = secure_import('log4j', allow_shells=False, allow_networking=False)
- This would disable log4j from opening sockets and execute commands, IN THE KERNEL.
- You can choose any policy you like for any module.

Useful References

Examples
F.A.Q
Installation
Mac OS Users - Disabling SIP for dtrace
Tracing processes
- Using dtrace
  - Tracing the syscalls of a process with pid 12345
    - dtrace -n 'syscall::: /pid == ($1)/ {@[pid,execname,probefunc]=count()}' 12345
  - Tracing the syscalls of a docker container with pid 12345
    - dtrace -n 'syscall::: /progenyof($1)/ {@[pid,execname,probefunc]=count()}' 12345
- Using strace
  - A script to list all your application's syscalls using strace.
    I contributed it to firejail a few years ago:
  - https://github.com/netblue30/firejail/blob/master/contrib/syscalls.sh
  - ```
  wget "https://raw.githubusercontent.com/netblue30/firejail/c5d426b245b24d5bd432893f74baec04cb8b59ed/contrib/syscalls.sh" -O syscalls.sh
  
  chmod +x syscalls.sh
  
  ./syscalls.sh examples/http_request.py
```
https://www.brendangregg.com/DTrace/DTrace-cheatsheet.pdf

TODO:

Node support (dtrace hooks)
Go support (dtrace hooks)
Allow/Block list configuration
Create a .yaml configuration per module in the code
- Use secimport to compile that yml
- Create a single dcript policy
- Run an application with that policy using dtrace, without using secure_import

FrCln / secimport