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Home » Hacking News » NISR06022002A: Oracle Remote Compromise

NISR06022002A: Oracle Remote Compromise

by Nikola Strahija on February 6th, 2002 A large part of Oracle database functionality is provided by PL/SQL packages. PL/SQL, or Procedural Language/ Structured Query Language, extends SQL and allows an "executable" package be created that exports procedures and functions. PL/SQL packages can be extended to call functions exported by operating system libraries or Dynamic Link Libraries. It is possible to create a (PL/SQL) library and PL/SQL package that calls any function in any library on the file system. An attack would probably call system() and pass the name of a program to be executed. It is apparent that to do this a user must be able to connect to the Oracle database server and login with an account that has the CREATE LIBRARY permission before an attack becomes successful. However, NGSSoftware Insight Security Research has discovered a way to fool the Oracle database server into loading arbitrary libraries and executing arbitrary functions without ever having to authenticate.


When a PL/SQL package executing in the database is required to run an
external procedure the oracle process connects to the Listener and requests
that the Listener load the relevant library, call the function and pass the
function any parameters passed to it. The Listener does not load the library
into its own process address space but rather launches another process,
extproc on Unix systems or extproc.exe on Windows platforms, and directs
oracle to connect to it. Oracle obliges and connects to the extproc process
using named pipes and makes the same request that it made to the listener.
Extproc loads the library and calls the function. There is no authentication
performed anywhere in all of this. This opens up a glaring and extremely
dangerous security hole.

It is possible for an attacker to masquerade as an Oracle process and
execute any function in any DLL on the file system. What exacerbates this
problem is that, even though communication normally goes over named pipes,
it can be forced to use sockets and can be done remotely. Because of this,
an attacker can write an exploit that
connects to the listener/extproc over TCP and, without ever having to
authenticate, run any function in any library they wish. A real world attack
would probably call system() exported by msvcrt.dll on Windows platforms or
exec() or system() exported by libc on unix platforms. Any operating system
command passed as a parameter to these functions would run in the security
context of the account running the oracle processes. On Unix systems this is
commonly the "oracle" user and on Windows NT/2000 this is, by default, the
local SYSTEM account. Needless to say that any commands executed as these
users will have dire consequences for the computer system involved.


Fix Information
***************
There are several things that can be done to help mitigate the risk of such
an attack. The first line of defense is, of course, with the use of a
firewall. No one should be able to access the listener port of 1521 from the
Internet. This not only helps mitigate the risk concerned with this problem
but a slew of others, too.

Moving to the Oracle database server itself, PLSExtproc functionality can be
removed if not needed. To do this remove the relevant entries in
tnsnames.ora and listener.ora. The PLS External Procedure service can have
many different names depending upon the system and Oracle version installed.
This could be icache_extproc, PLSExtproc
or extproc. It is also suggested that extproc(.exe) be deleted, too, on the
off chance that an attacker, replaces the entries in tnsnames.ora and
listener.ora.

If this functionality is required then it is possible to limit the machines
that may access the listener. Whilst this is a trust mechanism based only on
IP address it does help. The process is called "valid node checking" and
requires a modification to the sqlnet.ora file found in the
$ORACLE_HOMEnetworkadmin directory. Add the entries

tcp.validnode_checking = YES
tcp.invited_nodes = (10.1.1.2, scylla)

Replace 10.1.1.2 or Scylla in this example with the hosts that require
access. Any host not listed here will still be able to make a TCP connection
to the listener but the listener will simply terminate the connection.
Invited nodes should be restricted to machines that require access.

As another step towards help mitigating the risk, you could set the listener
listening on a non-default port (i.e. not 1521). Whilst this is not a great
solution, as anyone with a TCP port scanner has a highly likely chance of
finding the listener, it still helps.

Finally, on Windows NT/2000 the Oracle processes should not be running as
local SYSTEM. It is suggested that a low privileged account be created and
the Oracle processes run as this user. This account will need to be given
the "Logon as a service" account privilege.

Oracle was alerted to the theoretical vulnerability last summer and provided
with working exploit code in October and are currently investigating the
issue and working on a patch. NGSSoftware and Oracle have decided to release
this advisory in the interim of the patch becoming available so Oracle
customers may take steps to mitigate the
risk that may be posed to their Oracle database servers.

A check for this security hole has been added to the Oracle scan module of
Typhon II, NGSSoftware's vulnerability assessment scanner, of which more
information is available from the NGSSoftware website,
http://www.nextgenss.com/.



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