Since CISA killed it's RSS feed[1], If anyone is interested, I created an account here that will allow anyone to subscribe both via the fediverse and via RSS using the mastodon RSS feed for that account. The account is @cisareflector

1. https://www.cisa.gov/news-events/alerts/2025/05/12/update-how-cisa-shares-cyber-related-alerts-and-notifications