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pysandbox is a Python sandbox. By default, untrusted code executed in the
sandbox cannot modify the environment (write a file, use print or import a
module). But you can configure the sandbox to choose exactly which features are
allowed or not, eg. import sys module and read /etc/issue file.
Blocked Python functions (by default):
* Deny access to the file system
* Deny importing Python modules
* Deny exiting Python
* Deny access to stdin, stdout or stderr
* Deny some builtins symbols like execfile(), reload() or KeyboardInterrupt
* Deny execution of arbitrary bytecode (creation of arbitrary code object)
You can enable all of these features by setting the sandbox configuration.
The default recursion limit is 50 frames.
Protection of the namespace:
* Deny access to function closure, globals, defaults and code
* Deny access to frame locals
* Deny access to types subclasses
* __builtins__ is read only
* Deny access to dict methods able to modify a dict, eg. dict.__setitem__.
But you can use "d[key] = value" and "del d[key]" instead
pysandbox is unable to limit the memory or the CPU of the sandbox process: you
have to use your own protection. Use for example a subprocess to run the
untrusted code and use the OS to limit resources (memory and CPU) of the
subprocess. Using a subprocess protects also the main process against crash in
the untrusted code.
pysandbox is a sandbox for the Python namespace, not a sandbox between Python
and the operating system. It does not protect your system against Python
security vulnerabilities: vulnerabilities in modules/functions available in
your sandbox (depend on your sandbox configuration). By default, only few
functions are exposed to the sandbox namespace which limits the attack surface.
See Lib/test/crashers/ directory in the CPython source code to see examples of
known bugs crashing the CPython interpreter.
Use SandboxConfig class to configure your sandbox. Features are the most simple
way to configure it.
To enable a feature, use SandboxConfig('feature1', 'feature2', ...) or
config.enable('feature'). Available features:
- "codecs": codecs module
- "debug_sandbox": allow to display a traceback of the sandbox. Enable
traceback feature.
- "datetime": datetime module
- "encodings": encodings module with ascii, latin_1, utf_8, utf_16_be,
utf_32_be and rot_13 codecs (submodules). Enable codecs feature.
- "exit": sys.exit(), BaseException, KeyboardInterrupt, SystemExit, quit()
- "future": from __future__ import ...
- "hashlib": hashlib module.
- "help":, use "import pydoc" outside the sandbox to use it. Enable regex feature.
- "interpreter": give access to standard streams, enable traceback. Enable
encodings, exit, site, stdin, stdout, stderr and traceback features.
- "itertools": itertools module
- "math": math module
- "random": random module. Enable hashlib and math features.
- "regex": compile regex, match regex, search regex, etc. (re module)
- "site": allow to read the license file
- "stdin": sys.stdin, input() and raw_input()
- "stdout", "stderr": sys.stdout and sys.stderr
- "time": time module (except sleep, strptime and tzset functions)
- "traceback": compile() builtin, frame.f_code. Next calls to allowModule()
will add the module filename to the open() whitelist, so Python can display
a traceback with the source code. This feature have to be enabled before all
other features.
- "unicodedata": unicodedata module, required for u'\N{ATOM SYMBOL}' syntax
CPython restricted mode
WARNING: CPython restricted mode is unsafe because it is possible to execute
arbitrary bytecode.
Use SandboxConfig(cpython_restricted=True) to enable CPython restricted mode.
In this mode, reading a file and modify a class are blocked. Some attributes
are hidden (eg. method.__self__), other are read only (eg. func.__doc__).
CPython restricted mode is disabled by default. The restricted mode is
incompatible with SandboxConfig "traceback" feature and allowPath() method.
The restricted mode doesn't exist in Python3 anymore, it was removed with
bastion and rexec modules:
Other options
- config.allowPath(path) allows to read a file from the specified path
- config.allowModule(name, symbol1, symbol2, ...) allows to import the
specified module, but give only access to the specified symbols
With call() method: ::
from sandbox import Sandbox
def func(a, b):
return a + b
sandbox = Sandbox()
print, 1, 2)
With execute() method: ::
from sandbox import Sandbox, SandboxConfig
sandbox = Sandbox(SandboxConfig('stdout'))
sandbox.execute('print("Code executed in the sandbox")')
execute() with a local variable: ::
from sandbox import Sandbox, SandboxConfig
sandbox = Sandbox(SandboxConfig('stdout'))
sandbox.execute('print(data)', locals={'data': [1, 2, 3]}) # ok
sandbox.execute('data.append(4)', locals={'data': [1, 2, 3]}) # error
Objects passed to .call() globals/locals and .execute() arguments are
proxified: they are replaced by read-only views of the objects.
pysanbox is tested on Python 2.5 and 2.6 on Debian Sid.
See TODO file for the complete status.
See also
* tav CPython patches:
* secure*.py in plexnet
* Security in Python Wiki:
* Zope security:
* Brett Canon's "objcap" secured Python interpreter
* Python taint mode:
* Controlling Access to Resources Within The Python Interpreter:
* PyPy sandbox:
* mxProxy:
* Python 2.3: rexec and Bastion
Python-dev mailing list
* "Python jail: whitelist vs blacklist"
Victor Stinner, Tue Feb 24 13:50:40 CET 2009
* "Challenge: Please break this!"
tav, Mon Feb 23 23:41:30 CET 2009
* "Reviving restricted mode?"
Guido van Rossum, Sun Feb 22 17:45:27 CET 2009
* "object capability; func_closure; __subclasses__"
tav, Thu Jun 28 03:04:42 CEST 2007
* "Capabilities"
Guido van Rossum, Fri, 07 Mar 2003 12:41:16 -0500
(read the whole archive of march and april 2003)
* "Capability-based Financial Instruments"
Mark S. Miller, Chip Morningstar and Bill Frantz, 2000
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