![]() ![]() Always try to use a whitelisting approach: e.g.It is crucial to detect and block this kind of suspicious traffic as soon as possible in order to identify and isolate possibly infected hosts.įollowing some commonsense guidelines can already greatly reduce the risk and make things much harder for hackers and malware to contact their homes …īy default, restrict all outbound traffic and only allow what is necessary. Hackers and malware within your network will typically try to use these tunneling techniques to hide their tracks, exfiltrate data, contacts C2 (Command & Control) servers, … Obviously, the same principles and techniques as described above are also used by more malicious actors. We also have seen instances where state-of-the-art firewalls were misconfigured and could be tricked in allowing HTTP over port 443 or HTTPS over port 80 …Īnd in the end, if all of the above fails and since this is not a Red Team, we could still ask the customer to whitelist our box ? One option is to configure and use a HTTPS shell that might pass if HTTPS is not inspected at all. All traffic to that port on the VPS will be forwarded back to the SSH server on the Pwnie through the initial SSH tunnel (black line). At this point, we can remotely access the Pwnie bypassing the inbound enterprise firewall rules.įirewalls should be able to detect and block these ‘suspicious’ traffic flows, but even then, there are several other options. If the Pwnie can connect to the VPS over SSH, an initial SSH tunnel is created (big purple arrow). With remote port forwarding configured, port 2222 will be opened on the VPS. The diagram below shows an example of what actually happens. We will focus on the remote port forwarding, as this is the main technique used in this setup. It can be used for adding encryption to legacy applications but, in this case, it is (ab)used for opening a backdoor into the internal network. It is a built-in mechanism within SSH for tunneling application ports from the client machine (Pwnie) to a server machine (VPS) or vice versa. The main concept used here is SSH port forwarding or SSH tunneling. What you see-if anything-depends on whether connections have ever been made from the remote computer to the local computer. Or you may see a warning as the connection details are added to the list of recognized SSH hosts. Ssh -R 43022:localhost:22 may get a warning about having never connected to the local computer before. is the user account the remote computer is going to connect to on the local computer.Port 43022 was chosen because it is listed as being unallocated. The “43022:localhost:22” tells ssh that connection requests to port 43022 on the local computer should be forwarded to port 22 on the remote computer.The -R (reverse) option tells ssh that new SSH sessions must be created on the remote computer.On the remote computer, we use the following command. To have the SSH daemon start each time you reboot your computer, use this command: sudo systemctl enable sshd SSH will already be installed on your Linux computer, but you may need to start the SSH daemon (sshd) if the local computer has never accepted SSH connections before. It’s easier to set up than it is to describe. Reverse SSH tunneling allows you to use that established connection to set up a new connection from your local computer back to the remote computer. The answer lies in reverse SSH tunneling. You have an established connection between the two computers. That alone isn’t sufficient for your needs, however, because it doesn’t provide you with a working command-line session on the remote computer. It really doesn’t matter what the specific network issue is-this is useful whenever you can’t SSH straight to a remote computer.īut if the networking configuration on your end is straightforward, the remote computer can connect to you. That isn’t an option in the networking scenario we’re describing. Normally you’d fire up an SSH connection from the local computer and connect to the remote computer. To differentiate between the local and remote computers used in this article, the remote computer is called “howtogeek” and is running Ubuntu Linux (with purple terminal windows). The local computer is called “Sulaco” and is running Manjaro Linux (with yellow terminal windows). ![]()
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