Here webshell.asp is a directory but IIS parses it as a filename.
webshell.jpg will be ignored.
Filename parsing
Consider www.xxx.com/webshell.asp;.jpg
IIS does not parse the content after ;, so the filename becomes webshell.asp.
Default file extensions
IIS parses the following file extensions by default:
.asa
.cer
.cdx
Nginx Vulnerabilities
Filename parsing
www.xxx.com/webshell.jpg/idonotexist.php
If the rightmost file does not exist, the Nginx parser moves to the left by one. In this case, idonotexist.php does not exist, so webshell.jpg is parsed but it will be executed as .php.
Apache 1.x - 2.x Vulnerabilities
Filename parsing
webshell.php.test
Apache parses filename from right to left. If the current file type is not supported, the Apache parser moves to the left by one. Here .test is not supported by Apache, hence the file is parsed as webshell.php.
Configuration problems
AddHandler php5-script .php
This configuration makes webshell.php.jpg executed as webshell.php.
