Just 2 years ago I bumped into shodan.io through [Wayback] Onderzoekers: zestig slecht beveiligde Nederlandse scada-systemen op internet – Computer – Nieuws – Tweakers and saved the entry [Wayback] Shodan (website) – Wikipedia:
Shodan is a search engine that lets the user find specific types of computers (webcams, routers, servers, etc.) connected to the internet using a variety of filters. Some have also described it as a search engine of service banners, which are metadata that the server sends back to the client.[1] This can be information about the server software, what options the service supports, a welcome message or anything else that the client can find out before interacting with the server.
Shodan collects data mostly on web servers (HTTP/HTTPS – ports 80, 8080, 443, 8443), as well as FTP (port 21), SSH (port 22), Telnet (port 23), SNMP (port 161), IMAP (ports 143, or (encrypted) 993), SMTP (port 25), SIP (port 5060),[2] and Real Time Streaming Protocol (RTSP, port 554). The latter can be used to access webcams and their video stream.[3]
It was launched in 2009 by computer programmer John Matherly, who, in 2003,[4] conceived the idea of searching devices linked to the Internet.
It looked promising, but I was really pressed for time (having impromptu arrange all care for my mom, and became even more so when I got diagnosed with rectum cancer later that year), so did not pay much attention apart from registering.
Last year in the midst of my chemos I noted [Archive.is] Nate Warfield on Twitter: “https://t.co/16969jRfuL The latest Citrix vulnerability looks bad but there might be time to fix them before PoC comes out. The @shodanhq query above might help. (support.citrix.com/article/CTX269106 has more details)… “ (I think via @jilles_com) , so put it on my list of things to look into a bit further.
Since then, I found out a lot of people dislike Shodan and want to blacklist it because they see it as a threat. It feels like people think the internet is like the [Wayback] Ravenous Bugblatter Beast of Traal | Hitchhikers | Fandom
The Ravenous Bugblatter Beast of Traal is a vicious wild animal from the planet of [Wayback] Traal, known for its never-ending hunger and its mind-boggling stupidity. One of the main features of the Beast is that if you can’t see it, it assumes it can’t see you.
(This by the way is one of the reasons for Towel Day – Wikipedia)
Anyway: a few lists of Shodan IPv4 addresses and hostnames, and means to maintain them for the ones interested:
- [Wayback] wiki.ipfire.org – How to block Shodan scanners
- [Wayback/Archive.is] Shodan Scanning IP addresses : AskNetsec
- [Wayback] romcheckfail/shodan-ip-block-list: Used to bait shodan to scan your host, capture the IP address, then add it to a local blocklist.
- [Wayback] Blocking ALL SHODAN census server IPs · Issue #3 · stamparm/ipsum
Reality is that the internet is much smarter, so if you block Shodan from seeing you, others from the internet still will and if you have vulnerable services, one day they will be abused. For instance, this personal anecdote:
I forgot I had a port redirection on my router for RDP access a non longer existing Windows system any more. I forgot that this Windows machine had no fixed DHCP-lease while in use (it kept it’s lease as it was always on).
When that machine was long gone, another temporary Windows machine obtained the same internal machine (the router had been rebooted and after reboot hands out previously handed out IP address), and boom: the new Windows machine was bombarded with RDP logon requests.
In the end, the new Windows machine was not compromised, so I was lucky as it could have been.
Back when registering, shodan.io sent SMTP mail via sky.census.shodan.io, so you might want to not blacklist it if you blacklist at all (incidentally, when writing the IP address servicing that hostname was hosted in The Netherlands: [Wayback] 80.82.77.33 – sky.census.shodan.io – Netherlands – IP Volume inc – IP address geolocation).
It is good to think of you use Shodan, as not all usage might be legal where you live or where you travel to.
Some discussion in Dutch on the risks of using Shodan are in the above Tweakers.net link. It boils down to:
- Searching should be OK
- Accessing the devices found can be totally illegal
That’s basically with anything you find on the internet, for instance by Googling, so nothing new here.
I mainly use Shodan to see if I have any known vulnerabilities exposed. There are not that many ports open, but given the anecdote above, I might screw up again and not be so lucky.
This article has a balanced explanation of Shodan, how you use it, and how to stay safe: [Wayback] How to remove your device from the Shodan IoT search engine.
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