What is scanned for?
Below is an incomplete list of the kinds of scans and correlations that OnionScan supports.
When OnionScan detects a web server, it is scanned for the issues described in this section.
Apache mod_status Leak
This should not be news, you should not have it enabled. If you do have it enabled, attacks can:
- Build a better fingerprint of your server, including php and other software versions.
- Determine client IP addresses if you are co-hosting a clearnet site.
- Determine your IP address if your setup allows.
- Determine other sites you are co-hosting.
- Determine how active your site is.
- Find secret or hidden areas of your site
- and much, much more.
Seriously, don't even run the tool, go to your site and check if you have
reachable. If you do, turn it off!
Basic web security 101, if you leave directories open then people are going to scan them, and find interesting things - old versions of images, temp files etc.
Many sites use common structures
images/ etc. The tool checks for
common variations, and allows the user to submit others for testing.
Whether you create them yourself or allow users to upload images, you need to ensure the metadata associated with the image is stripped.
Many, many websites still do not properly sanitise image data, leaving themselves or their users at risk of deanonymization.
Sometimes, even without mod_status we can determine if two sites are hosted on the same infrastructure. We can use the following attributes to make this distinction:
- Server HTTP Header
- Technology Stack (e.g. php, jquery version etc.)
- Website folder layout e.g. do you use
/cssor do you use wordpress.
- Fingerprints of images
Some onion services use 3rd party analytics providers to track usage of their site. These providers often require a unique code to be embedded within the site - this code can be used to determine if two sites share a common operator or to find clearnet sites using the same code.
OnionScan extracts PGP identities from webpages in order to grab identifiers like email address / identities & GPG versions.
OnionScan collected information about SSH endpoints including software versions and the SSH public key fingerprint. These can be correlated against other onion services or clearnet servers in order to try and identifier the actual sever location.
FTP & SMTP
OnionScan collected information from other non-web servers, most notably software banners. These banners are often misconfigured to reveal information about the target server - including OS version, and sometimes hostnames and IP addresses.
The software version itself can also be a correlation vector.
OnionScan scans for common cryptocurrency clients including Bitcoin and Litecoin.
From these it extract other connected onion services as well as the user agent.
OnionScan also detects for the presence of many other protocols including IRC, XMPP, VNC & Ricochet.