Software Engineering Institute

Oracle Transparent Network Substrate (TNS ) Listeners are processes that receive connection requests from clients and return information for the clients to use to make database connections. The Listener Control Utility (LSNRCTL) is used to administer Listeners, and has the ability to establish an Oracle Net connection to remote Listeners. When used to administer a Listener, the Listener Control Utility parses the Listener's configuration file ($ORACLE_HOME/NETWORK/ADMIN/LISTENER.ORA for the default Listener).

The Listener Control Utility contains a format string vulnerability that could be exploited when the utility parses commands that are supplied directly to it or read from a Listener configuration file. By default, unauthenticated users can control Oracle Listeners and modify their configuration files. By inserting crafted entries containing format string specifiers into a Listener configuration file, an attacker could cause the Listener Control Utility to execute arbitrary code or commands or crash the utility, preventing its use by legitimate users. An attacker with sufficient privileges can supply crafted commands containing format string specifiers directly to a vulnerable Listener Control Utility.

In one possible scenario, an attacker could modify a Listener configuration file and wait for a legitimate user, such as a database administrator (DBA), to run the Listener Control Utility. Any code or commands supplied by the attacker would execute with the privileges of the user who ran the Listener Control Utility.

An unauthenticated remote attacker could execute arbitrary code or commands or cause a denial of service on a vulnerable system.

Apply a Patch

Apply the appropriate patch as referenced in Oracle Security Alert #40.

Restrict Access to the Listener Control Utility

Restrict access to Oracle Listeners to trusted users, hosts, and networks. Use firewall or router access control lists (ACLs) to restrict connections to the port(s) used by Oracle Listeners, 1521/tcp by default. Enable the Oracle Net feature called "TCP valid node checking" by modifying $ORACLE_HOME/NETWORK/ADMIN/SQLNET.ORA ($ORACLE_HOME/NETWORK/ADMIN/PROTOCOL.ORA in Oracle8i and prior releases) as follows:

tcp.validnode_checking = YES
tcp.invited_nodes = {list of IP addresses}
tcp.excluded_nodes = {list of IP addresses}
Configure Oracle listeners with encrypted passwords.

Set more restrictive file permissions on Listener configuration files ($ORACLE_HOME/NETWORK/ADMIN/LISTENER.ORA for the default Listener).

Disable the runtime modification of Oracle listener parameters by modifying $ORACLE_HOME/NETWORK/ADMIN/LISTENER.ORA as follows:

ADMIN_RESTRICTIONS_listener_name=on
Note that these workarounds are designed to limit access; they may not prevent exploitation of this vulnerability.