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Testing for DB Listener (OWASP-CM-002)

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OWASP Testing Guide v3 Table of Contents

This article is part of the OWASP Testing Guide v3. The entire OWASP Testing Guide v3 can be downloaded here.

OWASP at the moment is working at the OWASP Testing Guide v4: you can browse the Guide here

Brief Summary

The database (DB) listener is a network daemon unique to Oracle databases. It waits for connection requests from remote clients. This daemon can sometimes be compromised and hence can affect the availability of the database or the validity of data stored within it.

Description of the Issue

The DB listener is the entry point for remote connections to an Oracle database. It listens for connection requests and handles them accordingly. The testing outlined in this section is possible if the tester can access this service -- the test should be done from the Intranet (major Oracle installations don't expose this service to the external network). The listener, by default, listens on port 1521 (port 2483 is the new officially registered port for the TNS Listener and 2484 for the TNS Listener using SSL). It is a good practice to change the listener from this port to another arbitrary port number. If this listener is "turned off" remote access to the database is not possible. If this is the case, one's application would fail, resulting in a denial of service.

Potential areas of attack:

  • Stop the Listener - Create a DoS attack.
  • Set a password and prevent others from controlling the Listener - Hijack the DB.
  • Write trace and log files to any file accessible to the process owner of tnslnsr (usually Oracle) - Possible information leakage.
  • Obtain detailed information on the Listener, database, and application configuration.

Black Box testing and example

Upon discovering the port on which the listener resides, one can assess the listener by running a tool developed by Integrigy:

Listener Test.JPG

The tool above checks the following:
Listener Password On many Oracle systems, the listener password may not be set. The tool above verifies this. If the password is not set, an attacker could set the password and hijack the listener, albeit the password can be removed by locally editing the Listener.ora file.

Enable Logging The tool above also tests to see if logging has been enabled. If it has not, one would not detect any change to the listener or have a record of it. Also, detection of brute force attacks on the listener would not be audited.

Admin Restrictions If Admin restrictions are not enabled, it is possible to use the "SET" commands remotely.

Example If you find a TCP/1521 open port on a server, you may have an Oracle Listener that accepts connections from the outside. If the listener is not protected by an authentication mechanism, or if you can find easily a credential, it is possible to exploit this vulnerability to enumerate the Oracle services. For example, using LSNRCTL(.exe) (contained in every Client Oracle installation), you can obtain the following output:

TNSLSNR for 32-bit Windows: Version - Production
TNS for 32-bit Windows: Version - Production
Oracle Bequeath NT Protocol Adapter for 32-bit Windows: Version - Production
Windows NT Named Pipes NT Protocol Adapter for 32-bit Windows: Version - Production
Windows NT TCP/IP NT Protocol Adapter for 32-bit Windows: Version - Production,,

The Oracle Listener permits you to enumerate default users on Oracle Server:

User name	Password
OUTLN          OUTLN

In this case, we have not found privileged DBA accounts, but OUTLN and BACKUP accounts hold a fundamental privilege: EXECUTE ANY PROCEDURE. This means that it is possible to execute all procedures, for example the following:

exec dbms_repcat_admin.grant_admin_any_schema('BACKUP');

The execution of this command permits one to obtain DBA privileges. Now the user can interact directly with the DB and execute, for example:

select * from session_privs ;

The output is the following screenshot:


The user can now execute a lot of operations, in particular:

Listener default ports During the discovery phase of an Oracle server one may discover the following ports. The following is a list of the default ports:

1521: Default port for the TNS Listener. 
1522 – 1540: Commonly used ports for the TNS Listener
1575: Default port for the Oracle Names Server
1630: Default port for the Oracle Connection Manager – client connections
1830: Default port for the Oracle Connection Manager – admin connections
2481: Default port for Oracle JServer/Java VM listener
2482: Default port for Oracle JServer/Java VM listener using SSL
2483: New port for the TNS Listener
2484: New port for the TNS Listener using SSL

Gray Box testing and example

Testing for restriction of the privileges of the listener: It is important to give the listener least privilege so it cannot read or write files in the database or in the server memory address space.

The file Listener.ora is used to define the database listener properties. One should check that the following line is present in the Listener.ora file: ADMIN_RESTRICTIONS_LISTENER=ON
Listener password: Many common exploits are performed due to the listener password not being set. By checking the Listener.ora file, one can determine if the password is set:

The password can be set manually by editing the Listener.ora file. This is performed by editing the following: PASSWORDS_<listener name>. This issue with this manual method is that the password stored in cleartext, and can be read by anyone with acess to the Listener.ora file. A more secure way is to use the LSNRCTRL tool and invoke the change_password command.

LSNRCTL for 32-bit Windows: Version - Production on 24-FEB-2004 11:27:55
Copyright (c) 1991, 2002, Oracle Corporation.  All rights reserved.
Welcome to LSNRCTL, type "help" for information.
LSNRCTL> set current_listener listener
Current Listener is listener
LSNRCTL> change_password
Old password:
New password:
Reenter new password:
Connecting to <ADDRESS>
Password changed for listener
The command completed successfully
LSNRCTL> set password
The command completed successfully
LSNRCTL> save_config
Connecting to <ADDRESS>
Saved LISTENER configuration parameters.
Listener Parameter File   D:\oracle\ora90\network\admin\listener.ora
Old Parameter File   D:\oracle\ora90\network\admin\listener.bak
The command completed successfully