Picture Trojan principle production prevention

Definition

Picture Trojan horse is a picture containing a Trojan horse （ It's usually a one sentence Trojan horse ）

principle

Take file upload vulnerability as the basic condition , Write executable conditions into the picture , Then use the file containing vulnerability to execute a sentence Trojan horse in the picture , So as to obtain the permission of the target server .

Production methods

One 、copy

Pictures and a sentence Trojan horse , open cmd, Enter folder
copy 1.jpg/b+1.php/a 2.jpg
among /b Represents opening a file in binary encoding ,/a Representative to ASCII Code to open the file

Two 、 Using binary encoding tools

Add directly anywhere in the code webshell that will do , It can be used with ant sword .

To guard against

● The directory for file upload is set to be non executable
● Determine file type
● Use random number to overwrite file name and path