rstconn 0.3.1

A TCPKill utility written in python and scapy

RSTconn

A TCPKill is a utility that implements a TCP reset attack for IPv4 and IPv6 written in python and scapy.

RESET is a flag in TCP packets to indicate that the connection is not longer working. If any of the two participants in a TCP connection send a packet contains such a RESET flag, the connection will be closed immediately.

Thus it can be use to attack TCP connections once the attacker can forge TCP packets from any of the two parties if he or she know their IPs, ports and the sequence number of current TCP connection.

The attack can be used to make certain users to fail to use certain network services based on TCP if we know the information above.

In practice, we should eavesdrop the victims’ communications to get their IPs, ports and the sequence number.

You can do it by filtering the TCP packets and find the newest packets that we want to attack.

We can sends a TCP packet with RESET flag and the IPs and ports of source and destination are sniffed from victims. What’s more, the sequence number will increase in TCP communication, its value should be equal or lager than the ack value from the lastest packet the sender received and in the window of receiver. So we should update it. To ensure successful, we can send lots of packets with different sequence number which is larger than the sniffed ack field.

Setup

pip install rstconn

Usage

rstconn kills network connections.

optional arguments:
  -h, --help            show this help message and exit
  --iface {lo,enp0s25,lxcbr0,docker0,br-d316e57def52,vethd4f41f0,veth6fa5336, ...}, -i {...}
                        Interface where to listen to
  --server-ip SERVER_IP, -sip SERVER_IP
                        IPv4 or hostname
  --client-ip CLIENT_IP, -cip CLIENT_IP
                        IPv4 or hostname
  --server-port SERVER_PORT, -p SERVER_PORT
                        Server port
  --packet-count PACKET_COUNT, -pc PACKET_COUNT
                        listen for a maximum of N packets
  --seq-jitter SEQ_JITTER, -sj SEQ_JITTER
                        Set seq_jitter to be non-zero in order to prove to yourself that the
                        sequence number of a RST segment does indeed need to be exactly equal
                        to the last sequence number ACK-ed by the receiver
  --ignore-syn, -is     if a Packet has SYN flag, not sending RST
  --window-size WINDOW_SIZE, -ws WINDOW_SIZE
                        Window size
  -d {CRITICAL,ERROR,WARNING,INFO,DEBUG}, --debug {CRITICAL,ERROR,WARNING,INFO,DEBUG}
                        Debug level, see python logging; defaults to INFO if omitted
  -m, --monitor         Just sniff traffic without sendin RST
  -v, --version         Print version and exit

RSTconn listens for the matching connections and than sends a number of SYN/ACK and RST packets to the client to get the connection be killed.

The number of packets is configurable by --packet-count, --iface and --server-ip and --server-port are related to the local server port to be listen on.

rstconn -i lo --server-ip 127.0.0.1 --server-port 8000 --packet-count 50

Demo

apt install netcat

• Setup TCP connection. In one terminal window run nc -nvl 8000 to set up a server
• In another terminal window run nc 127.0.0.1 8000 to connect to the server
• In a third window run rstconn to run our sniffing program

You should see the sniffing program log some output, send a RST packet, and the nc connection should be broken.

If you want to test rstconn in IPv6, use instead:

• nc ::1 8000
• nc -nvl ::1 8000
• rstconn -i lo --server-ip "::1" --server-port 8000 -pc 33

Usage examples

Reset connections to ftp.gnu.org

rstconn -i enp0s25 --server-ip ftp.gnu.org -pc 33

on the client side we'll see

ftp> ls
421 Service not available, remote server has closed connection

Credits

• https://gist.github.com/spinpx/263a2ed86f974a55d35cf6c3a2541dc2
• https://github.com/robert/how-does-a-tcp-reset-attack-work

References

• Watson, P.: Slipping in the Window: TCP Reset attacks. (2004)