security/Subdomainについて、ここに記述してください。

https://www.theregister.com/2021/06/30/subdomain_vulnerabiilties/

Subdomain security is substandard, say security researchers

The team scanned 50,000 of the world’s most important web sites as ranked by the Tranco list, and found 1520 vulnerable subdomains across 887 sites.

https://tranco-list.eu/list/ZKYG/1000000

This list aggregates the ranks from the lists provided by Alexa, Majestic, and Quantcast from 24 February 2020 to 24 March 2020 (30 days).