Lists of filters for adblockers and firewalls.
FilterLists API is a free Security API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
FilterLists is the independent, comprehensive directory of filter and host lists for advertisements, trackers, malware, and annoyances. By Collin M. Barrett.
Details from filterlists.com.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
DNS, WHOIS/RDAP, SSL, subdomain enumeration, and email security in one parallel call
The FilterLists API is provided by FilterLists (filterlists.com). FilterLists is the independent, comprehensive directory of filter and host lists for advertisements, trackers, malware, and annoyances. By Collin M. Barrett.
Yes. The FilterLists API is listed in the Security category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
No. The FilterLists API requires no authentication, so you can start making requests without signing up.
CORS support for the FilterLists API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The FilterLists API is served over HTTPS, so it's safe to use in production.