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Oracle DBMS Access Control Bypass in Login
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SUMMARY
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.
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.
DETAILS
Vulnerable Systems:
* Oracle 8i (8.1.7.x.x)
* Oracle 9i (9.2.0.7)
* Oracle 10g Release 1 (10.1.0.4.2)
* Oracle 10g Release 2 (10.2.0.1.0)
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.
Disclosure Timeline:
Vendor notified on 02-Nov-05
Patch released on 17-Jan-06 (5745699 OAUTH - REMOTE AUTHENTICATED ESCALATE
TO DBA VIA AUTH_ALTER_SESSION)
ADDITIONAL INFORMATION
The information has been provided by <mailto:shulman@imperva.com>
shulman.
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