Summary

Oracle native authentication protocols are typical challenge-response
protocols. After some negotiation the client sends the username. If
the user exists the server sends an encrypted key. The client uses
the key to encrypt the user's password and sends it to the server.
One of the protocols is documented quite well in [1.]. On reading
that description it is quite obvious that the protocol is vulnerable
against the off-line brute force attack. Oracle changed the algorithm
in 9i and changed it again in 10g. If we use the OCI driver, our
programs will use these newer protocols, but thin drivers use the
older version, thus implementing an off-line brute forcer is not
absolutely pointless (if you can sniff the connection you can conduct
several other attacks of course). The servers and the clients support
the older version of the protocol, thus it is worth a research
whether downgrade attack is possible.

This article describes four versions of the Oracle native
authentication. These information are based on [3.]. This description
is shorter than [3.] and just emphasizes those differences that could
be important in a downgrade attack againts the (SEEMS TO BE stronger)
newer authentication protocols.

We do not disclose the details of the downgrading. In the Downgrading
chapter you can find screenshots about a successful attack to prove
that downgrading is possible.

Detailes

The full anouncment can be found at
http://www.pwc.com/extweb/service.nsf/docid/3AC99308583CCE398025727400391E31/$file/oraauthdg_pub.pdf

Solution

There are two solutions to these kind of problems:

• Use strong passwords so a brute force attack is not feasible
• Use encryption in the communication channel

Credits

Article is written by Laszlo Toth.
Special thanks goes to Balazs Boda, Lajos Antal and Pete Finnigan

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