A reverse shell is a type of shell in which the primary function is to enable an attacker to gain remote access to and control of a machine . This is achieved by the attacker sending commands through the reverse shell which are executed on the target machine . In many cases, a reverse shell may be used to bypass firewalls or other security measures that have been put in place on a network or system . In some cases, an attacker may even be able to use built-in tools such as telnet or ssh . The choice of tool will often depend on what is available and what privileges the attacker has . This provides them with a great deal of power and flexibility when it comes to carrying out attacks .Authentication failed. Unique API key is not valid for this user.