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Oracle DBMS Access Control Bypass in Login
From: shulman () imperva com
Date: 17 Jan 2006 20:18:12 -0000

Oracle DBMS – Access Control Bypass in Login
Oracle is a widely deployed DBMS. Clients use a protocol called TNS to communicate to the Oracle server. Protocol 
messages are used for session setup, authentication and data transfer. The standard authentication mechanism requires a 
client to supply a valid pair of user name and password.
Imperva’s Application Defense Center is conducting an extensive research of the TNS protocol and its implementation. As 
part of the research the team has identified a severe vulnerability in Oracle’s access control mechanism.
During the login process an Oracle user with no more than “create session” privileges can execute commands in the 
context of the special database user SYS. This of course grants any user the highest administrative privileges possible.
The authentication part of the protocol is comprised of two steps, including two different client requests and two 
server responses respectively. The first request (message code 0x76) contains only the user name while the second 
(message code 0x73) contains the user name and an obfuscated password. 
This second request also contains a list of name-value pairs describing various attributes of the client. The value 
named “AUTH_ALTER_SESSION” is intended for setting up session attributes related to the locale and language, in the 
form of an ALTER SESSION SQL statement.
It turns out that this value can contain any SQL statement. Moreover, this command is executed in the context of the 
SYS user, which operates outside of the Oracle access control mechanism. Thus, by setting the value of 
“AUTH_ALTER_SESSION” to an arbitrary SQL statement an attacker can execute any arbitrary command in the database. In 
particular, the attacker can create a new database account and create DBA privileges to the new account.
Notice that if the attacker tries to execute “GRANT DBA TO attacker_account” a deadlock occurs and attacker_account 
cannot login to the database until the connection is closed.
Change the value of the AUTH_ALTER_SESSION attribute in TNS authentication message.
Tested Versions
Oracle 8i (8.1.7.x.x)
Oracle 9i (
Oracle 10g Release 1 (
Oracle 10g Release 2 (
Not Vulnerable
Vendor’s Status
Vendor notified on 02-Nov-05

Copyright (c) 2006 Imperva
Redistribution of this alert electronically is allowed as long as it is not edited in any way. To reprint this alert, 
in whole or in part, in any medium other than electronic medium, please email adc () imperva com for permission.

The information within this advisory is subject to change without notice. Use of this information constitutes 
acceptance for use in an AS IS condition. Any use of this information is at the user's own risk.  There are no 
warranties, implied or express, with regard to this information. In no event shall the author be liable for any direct 
or indirect damages whatsoever arising out of or in connection with the use or spread of this information.

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