The saboteur But the risk of incrementing the SCN via the backup bug is not the only cause for concern. Perhaps the most important part of our finding is that the SCN can be incremented by anyone who can issue commands on an interconnected database.
Say there's a low-privilege reporting database system that has a read-only database link to a high-privilege database somewhere down the line. All someone has to do is issue a few administrative commands on that low-privilege database to raise the SCN value by, for example, 1 trillion; the next time the high-privilege database receives a connection from that box, its SCN increases to the higher level. It's simple enough to verify the current SCN value, so running a command to push it a few ticks shy of the soft limit is trivial.
Using this technique, a bad actor could potentially cause a systemwide Oracle database communications failure, a shutdown, or a crash with only a few commands on a sideline server -- or even craft a bit of code to mimic a connecting instance. It may be possible, though more challenging, to cause the same problems though a SQL injection attack on a vulnerable application.
Our discovery of this attack method and our communication of this information to Oracle resulted in Oracle's request that InfoWorld hold this story until today, when a patch could be made available. In addition to the method we discovered, we learned of two other, similar means of incrementing the SCN by searching the open Web, although these required higher privilege levels. The patch blocks all three methods that we are aware of, though there may be others.
The realityThe SCN is a moving line that cannot be crossed. The line moves up by 16,384 every second; as long as the SCN growth rate is slower, all should be well.
But what happens when your SCN moves closer and closer to that line due to the spurious jumps caused by the backup bug, a simple mistake by an admin, or other means? How do you deal with this impending problem?
The answer: Shut down the database servers for a while so that the number stops incrementing.
Plainly put, this means that every single interlinked Oracle instance across an entire company will need to be shut down just to move a bit further away from the line. If only a handful are shut down, they will very quickly jump right back to the high SCN whenever they connect with other Oracle instances. The only way to ensure this problem is completely eradicated is to shut down every affected system: backup servers, replicas, everything.
Not only that, but while they're down, admins will need to scour the infrastructure to be absolutely certain that no affected Oracle systems have escaped remediation. If they miss even one instance, they will have to perform the complete shutdown again.