Hostnames coming to Spamhaus Domain Blocklist (DBL) for increased accuracy

EDITORS NOTE Feb 1st, 2022: The Spamhaus Domain Blocklist (DBL) with hostnames is now in production and can automatically be accessed by anyone using the DBL via the Data Query Service or Rsync.

Listing legitimate domains

Part of the Spamhaus Domain Blocklist (DBL) details legitimate domains that cybercriminals have compromised; it’s called “abused-legit.”

A legitimate domain with a good reputation is a precious commodity to a bad actor. It can assist them with avoiding immediate detection (and the subsequent listing on a blocklist), enabling them to run a malicious campaign for longer. Therefore, it will come as no surprise that it’s worth their while to go to the effort of hacking a content management system (CMS), for example, WordPress, to get their hands on a domain that has been nurtured and used appropriately.

Once a web server or CMS is compromised, a bad actor places a file to redirect visitors’ browsers to their malicious website – a phishing or malware dropper site. Then they use the legitimate domain’s URL in emails, texts or posts, to lure people to the fraudulent webpage(s).

There’s a drawback to these kinds of listings…

In these circumstances, when a compromised domain is listed, the second-level domain and top-level domain (TLD) are listed in the DBL; however, this can cause issues.

Take, for example, a multi-site like the well-known website design site, wix.com, which has millions of subdomains associated with its second-level domain. Every free Wix site has the following URL structure:

So if https://example-accountname.wixsite.com/example_website were compromised, then the second level and TLD would be listed, i.e., “wixsite.com” in the DBL. This would block every free Wix website URL. Not ideal.

Hostnames to the rescue

To prevent this from happening, the DBL abused-legit will soon list hostnames instead.

As you can see from the above image, a hostname consists of the subdomain(s), the second-level domain, and the TLD. This means the listing is more targeted. In the case of the WIX example, only the compromised site will be listed and blocked, not all of them.

What are the benefits?

Here are just a few of the benefits of this change to the DBL:

• Users of the DBL abused-legit will see a reduction in the number of false positives they experience.
• Users of the DBL abused-legit will be able to make more informed decisions regarding how they treat email messages, e.g., this message needs to be rejected, not placed in the spam folder.
• Legitimate domain owners won’t be inconvenienced. No longer will their domain be listed on a blocklist when another website on the same second-level domain is compromised.

When are these changes coming to the DBL?

From Tuesday, February 1st, 2022, the DBL abused-legit will be listing hostnames for users of the Data Query Service (DQS) and rsync. It’s worth noting that rsync users will need to check their configuration (see below for further information).

Hostnames will not be available to those of you who use the Spamhaus Project’s free DNSBLs available via their Public Mirrors. So we recommend you move across to the free Data Query Service – reconfiguration only takes minutes, and you get access to additional blocklists.

Want to test the beta version of the DBL with hostnames?

If you want to test the new DBL with hostnames, it’s now available via the Spamhaus Project’s free public mirrors dbl-beta.spamhaus.org.

How? If you’re using one of our plug-ins for SpamAssassin or Rspamd we have beta versions to use alongside the beta DBL with hostnames. See the configuration updates here for SpamAssassin or here for Rspamd.

How long will the beta zone be available? Only until Monday, January 31st, 2022. So REMEMBER – put a reminder in your calendar to move back to dbl.spamhaus.org on January 31st, 2022!!!

Using the DBL via rsync?

As mentioned, on February 1st, 2022, we will change the DBL file you currently download to incorporate hostnames for abused-legit rather than wild card domains.

For anyone consuming the data in an rbldnsd setup, this shouldn’t cause any issues. However, if you’re doing something a little different with the data, you may need to make changes, so please check now, not on January 31st, 2022.

Using legacy SpamAssassin or Rspamd configurations?

If you rely on legacy configurations for either of the above spam filters and do NOT query full hostnames but reduce them to the base domain, you won’t be able to take advantage of the hostname-based component unless you tweak (a highly technical term) your system/config accordingly. This won’t cause you operational issues, but you won’t be able to use abused-legit listings out of the box.

Also, remember that if you want to test the beta version and use our plug-ins, for either SpamAssassin or Rspamd, you need to update the code (see “Want to test the beta version of the DBL with hostnames”).

We’d love your feedback

If you are using the beta zone and have any comments, issues, or suggestions, please reach out to us with your feedback. You can either send us a message using this form or send us a tweet.