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Dangerous Commands to Disable Linux UNIX Server

Oracle Database Tips by Donald BurlesonAugust 27, 2015

When folks talk about UNIX security and the tools available to prevent mishaps, it is important to remember just how fragile the UNIX environment can be. The primary job of the UNIX Oracle DBA is keeping the database running, so they are not usually  surprised to see how easy it is to clobber a server.

The script below cripples the UNIX server by an implosion of incoming jobs. This is known as a Denial Of Service (DOS) attack, and the Oracle DBA should be aware just how easy it is for a hacker to make a mess in UNIX.

Interestingly, the use of  a DOS attack is not new and mainframe programmers have known how to clobber a mainframe job intiator since the 1960's.

The same kind of attack can be launched against IBM mainframes by creating a recursive IEFBR14 job that directs its SYSOUT to the mainframe internal reader.

The following is a section of JCL that illustrates the recursive job submission technique.

//EXEC  IEFBR14
//DD SYSIN=IBM.MISC(CRASH),DISP-SHR
//DD SYSOUT=(,,INTRDR)

WARNING:  The following command will clobber any UNIX server in a matter in just a few seconds.  This script is provided for illustration purposes only, and it should not ever be run in a production environment:

nohup /tmp/recursive.ksh > /dev/null 2>&1 &
The recursive.ksh file submits two of the same tasks.
nohup /tmp/recursive.ksh > /dev/null 2>&1 &
nohup /tmp/recursive.ksh > /dev/null 2>&1 &

Because the job submits itself, two jobs submit 4, four submit 16, and so on, until the entire server in unable to accept any work.

Again this script is described as a warning to any cocky Oracle DBA who assures management that their UNIX server is impervious to DOS attacks.

 

 
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