Weevely is a stealth PHP web shell that simulate telnet-like connection. It is an essential tool for web application post exploitation, and can be used as stealth backdoor or as a web shell to manage legit web accounts, even free hosted ones.

Official website:

http://epinna.github.com/Weevely/

Getting started with a quick Tutorial:

https://github.com/epinna/Weevely/wiki/Tutorial

Or show list of available Modules and backdoor Generators:

https://github.com/epinna/Weevely/wiki/Modules-list
https://github.com/epinna/Weevely/wiki/Generators-list

Main features:

* More than 30 modules to automatize administration and post exploitation tasks
  o Execute commands and browse remote filesystem, even with PHP security restriction
  o Audit common server misconfigurations
  o Run SQL console pivoting on target machine
  o Open HTTP proxy to tunnel your traffic through target
  o Simple file transfer from and to target
  o Spawn reverse and direct TCP shells
  o Bruteforce passwords of target system users
  o Run port scans from target machine
  o And so on..

* Backdoor communications are hidden in HTTP Cookies
* Communications are obfuscated to bypass NIDS signature detection
* Backdoor polymorphic PHP code is obfuscated to avoid HIDS AV detection

Weevely author keep Dissecting, a security related blog:

http://disse.cting.org/