SSH Honeypots (Ab)used as Proxy

Published: 2016-03-13
Last Updated: 2016-03-14 08:23:10 UTC
by Xavier Mertens (Version: 1)

I’m operating a small group of SSH honeypots (located in Belgium, Canada & France) and I’m of course keeping an eye on it every day. Collected data are sent to DShield and to my Splunk instance. A small reminder: if you’ve a spare Raspberry Pi lying around, why not deploy a honeypot and help us to collect more data? Johannes posted a script to automate the setup and is looking for beta testers!

Cowrie is a wonderful honeypot. Not only, it tracks login attempts and, when the attacker successfully connected, it also simulates a real server with a fake file system and commands. But it can also simulate "Direct-TCP" requests. This is a nice feature offered by SSH servers that allow a user to create TCP sessions inside the SSH tunnel. This feature is called "Port Forwarding". It is used by many people who need to access a service not directly reachable from their current location. Example: you have a web interface to manage an appliance that is not available but you have a SSH server in the same subnet. Just do this: (The appliance is 192.168.254.10, the SSH server is 192.168.254.2)

$ ssh -L 8443:192.168.254.10:443 user@192.168.254.2

Then point your browser to https://127.0.0.1:8443/.

More interesting: To surf the web anonymously, you can use dynamic port forwarding with the '-D' flag:

$ ssh -D 8080 user@192.168.254.10

Then, configure your browser to use 127.0.0.1:8080 as a SOCKS proxy and you will surf the web with a source IP address of 192.168.254.10.

Note: This feature is enabled by default in OpenSSH and can be disabled by adding 'AllowTcpForwarding No' to your sshd_config. With SSHv2, you can also only permit some users or groups to use this feature.

If it's so easy and useful for good people, you can imagine that it's even more interesting for attackers that could then hide their IP address. A few days ago, I detected an unusual amount of events generated by some of my honeypots. Regarding my honeypots, there was an huge increase of “Direct-TCP” requests over the past 7 days:

Event	Hits
cowrie.direct-tcp.request	24242
cowrie.direct-tcp.data	22967
cowrie.log.open	15130
cowrie.log.closed	14679
cowrie.session.connect	13882
cowrie.session.closed	13877
cowrie.command.success	11563
cowrie.client.version	9019
cowrie.login.success	8652
cowrie.command.failed	3948

A closer look to the "Direct-TCP" requests shows clear a peak of activity for the last days:

The most affected honeypots are the ones located in France (Paris) and Canada (Ontario). The top attackers were located in the following countries:

Country	Hits
Germany	22405
Russia	1295
United States	267
Argentina	76
France	51
Switzerland	35
Netherlands	26
Ukraine	20
India	16
Iran	16

Germany came in first place just with two distinct IP addresses. And what about the destination? Here is the top-10:

The attackers tried to use the honeypot mainly for mail and web traffic, based on this top-10 destination ports:

TCP Ports	Hits
80	31431
25	1428
587	383
443	271
465	160
110	30
143	13
1101	4
1102	4
89	1

If we analyze the relations between the honeypots, sources and destinations, we see that some destinations (blue) were targeted by more than one attacker (green) connected on different honeypots (red):

About the web traffic, the top destinations were:

www.google-analytics.com
tags.tagcade.com (an ads tag management system)

Some people trying to abuse those services? Feel free to share your findings if you also detected such kind of activity!

To conclude: attackers are not only scanning the Internet to find vulnerable hosts and turn them in bots. They are also looking for ways to hide themselves to perform (maybe) more complex or dangerous attacks.

And keep in mind that if you allow users to SSH to systems that can access the Internet, they can be used as a solution to bypass classic controls in place!

Xavier Mertens
ISC Handler - Freelance Security Consultant
PGP Key

Keywords: ssh proxy honeypot cowrie

10 comment(s)

Join us at SANS! Attend Reverse-Engineering Malware: Malware Analysis Tools and Techniques with Xavier Mertens in Online | Japan Standard Time starting Nov 07 2022