[Lotus Black]

Requirement: You need to get Admin access in wordpress site
So when you got admin access, login with admin username and password

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Go to Appearance>Theme>Editor you will see Default Theme, in my case, Nice Hotel
You can shell upload in there,

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but, i just change to another theme, Twenty Eleven Theme, so it will be looks like

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And click to 404 Template.

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Edit 404 Template php code and replace with your own shell code just like below. You need to update php file by clicking Update File

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Now, you shell link will be www.someone.com/wp-content/themes/twentyeleven/404.php
Cause i change to Twenty Eleven Theme, it depend on your choice and it may be variable.

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Sorry for my poor english, but i hope my tutorial is understandable.

Regards
Lotus Black

[Cressi]

Nice guide, and great tutorial ^^ Thanks for the share.

[Customer]

I remember when Kirito made a tutorial for this a while ago, shit was so cash.