CodeSafe

An open-source Python library for code encryption, decryption, and safe evaluation using Python's built-in AST module, complete with allowed functions, variables, built-in imports, timeouts, and blocked access to attributes.

CodeSafe is an experimental library, and we're still running some tests on it. If you encounter any issues, or have an edge use case, please let us know.

Note

CodeSafe is intended to quickly encrypt/decrypt code files, and run them (only for Python script files) while in their encrypted form, but not as a means for powerful encryption, just code obfuscation. We have also included a safe_eval function, that can safely evaluate expressions within a safe environment.

Security Advisory

Critical Vulnerability Fixed in v0.0.5

Versions 0.0.1 through 0.0.4 contain a known sandbox escape vulnerability in safe_eval() that allows arbitrary code execution.

• Vulnerability: The safe_eval() function in versions 0.0.1-0.0.4 is vulnerable to a sandbox escape via indirect subscript lookup (e.g., __builtins__['exec'](...)). This bypasses the AST validation and allows execution of arbitrary Python code.
• Impact: An attacker controlling an expression passed to safe_eval() can execute arbitrary Python code with the application's permissions.
• Affected Versions: 0.0.1, 0.0.2, 0.0.3, 0.0.4
• Fixed In: Version 0.0.5 and later

If you are using any version from 0.0.1 to 0.0.4, you should upgrade to version 0.0.5 or later immediately. These earlier versions should not be used in untrusted expression evaluation environments.

The fix includes:

1. Rejecting all ast.Call nodes unless the exact target is explicitly whitelisted (including calls via subscript, attribute, and other indirect targets)
2. Using a minimal built-ins allowlist that excludes dangerous functions like exec, eval, compile, and __import__
3. Added comprehensive regression tests for indirect call targets

A huge thanks to @hkmj19/Linkedin for finding and reporting this vulnerability.

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Vulnerability & Security Testing (test_poc.py)

CodeSafe v0.0.5+ includes a rigorous test suite (TestVulnerabilityFixes and TestEdgeCases in test_poc.py) to systematically verify that safe_eval blocks sandbox escapes while preserving standard evaluation features.

Test Results Summary

49/49 Security & Edge Case Tests Passing (100% Pass Rate across all vector categories)

Attack Vector / Category	Specific Vectors Tested	Status
AST Subscript & Indirect Calls	__builtins__['exec'](), __builtins__['eval'](), __builtins__['__import__'](), getattr(__builtins__, 'exec'), nested subscript access	[PASS] Blocked
Dunder Attribute Escapes	__class__, __bases__, __mro__, __subclasses__, __globals__, __closure__, __code__	[PASS] Blocked
Class Hierarchy Traversal	object.__subclasses__(), type().subclasses()	[PASS] Blocked
Expression Bypasses	Comprehensions (list, dict, set), generator expressions, short-circuit logic (and/or), ternary operators, tuple unpacking, walrus operator (:=), lambda calls	[PASS] Blocked
Module & I/O Execution	Direct/from import, os.system, subprocess, io.open, socket, requests, urllib, pathlib write operations	[PASS] Blocked
Dangerous Built-ins	exec(), eval(), compile(), input(), open() (default settings), modifying __builtins__	[PASS] Blocked
Functional Baseline	Safe arithmetic, string/list/dict operations, standard safe builtins (len, max, abs), explicitly allowed functions	[PASS] Working

Running the Proof of Concept Tests

To run the security PoC suite locally:

python -m unittest test_poc.py -v

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Changelog v0.0.5:

• Security Fix: Patched critical sandbox escape vulnerability in safe_eval() (CVE pending), thanks to @hkmj19/Linkedin for reporting.
• Blocked indirect function calls via ast.Subscript, ast.Attribute, and other non-ast.Name targets
• Implemented minimal safe builtins whitelist excluding exec, eval, compile, __import__, and similar dangerous functions
• Added regression tests for indirect call bypass attempts

Changelog v0.0.4:

• Major performance optimizations for encryption and decryption (~10x speedup).
• Optimized safe_eval by pre-filtering builtins and reducing internal overhead.
• Added support for bytes input in encrypt.
• Added support for file-like stream objects in run and decrypt_to_file.
• Standardized error handling (replaced print with exceptions).

Changelog v0.0.3:

• Added an allow_attributes parameter to safe_eval and set immediate_termination to be True by default for safer function calling.

Changelog v0.0.2:

• Fixed function returns.
• Added error handling to CodeSafe, removed some print statements with edits from @0XC7R.

Changelog v0.0.1:

• Initial release

Installation

You can install CodeSafe using pip:

pip install codesafe

Supported Python Versions

CodeSafe supports the following Python versions:

• Python 3.6
• Python 3.7
• Python 3.8
• Python 3.9
• Python 3.10
• Python 3.11/Later (Preferred)

Please ensure that you have one of these Python versions installed before using CodeSafe. CodeSafe may not work as expected on lower versions of Python than the supported.

Features

• Safe Eval: Safely allow eval() expressions to run, while maintaining complete control over the entire evaluation process.
• Code Encryption/Decryption: Quickly encrypt your code. This is meant for code obfuscation, and not high-level encryption.
• Run encrypted code at runtime: Run your encrypted code files, without needing to expose your code to end-users.

Note

Running encrypted files at runtime using run() are only available in formats that can be understood by Python.

Important

When running safe_eval, make sure to wait for the Python file to finish its bootstrapping phase. This can be done by simply waiting for:

if __name__ == '__main__':
   # Run eval, etc.

If you're planning on including safe_eval in executables:

import multiprocessing
if __name__ == '__main__':
      multiprocessing.freeze_support()
      # Call safe_eval afterwards

You can read more about why this needs to be done here: https://pytorch.org/docs/stable/notes/windows.html#multiprocessing-error-without-if-clause-protection

Usage

Safe Eval

from codesafe import safe_eval

if __name__ == '__main__':
    # Run a normal, safe expression
    expression = "1 + 1"
    disallowed_expression = "os.getcwd()"

    result1 = safe_eval(expression, timeout=10, immediate_termination=True)
    result2 = safe_eval(disallowed_expression, timeout=10, immediate_termination=True)

Note

Attribute inspection is disabled when using safe_eval. You can read more about how to use safe_eval from here.

Encrypt & Run Code

from codesafe import encrypt_to_file, decrypt_to_file, run

code = """
greetJohnny = "Hello Johnny!"

def greet_someone(greeting):
    print(greeting)

greet_someone(greetJohnny)
"""

# Encrypt the code
encrypted_file_path = "encrypted_code.encrypt"
encrypt_to_file(code, encrypted_file_path)

# Run the encrypted code
run(encrypted_file_path) # Hello Johnny!

# Decrypt code to another file
output_file = "decrypted_code.py"
decrypt_to_file(encrypted_file_path, output_file)

Contributing

Contributions are welcome! If you encounter any issues, have suggestions, or want to contribute to CodeSafe, please open an issue or submit a pull request on GitHub.

License

CodeSafe is released under the terms of the MIT License (Modified). Please see the LICENSE file for the full text.

Modified License Clause

The modified license clause grants users the permission to make derivative works based on the CodeSafe software. However, it requires any substantial changes to the software to be clearly distinguished from the original work and distributed under a different name.