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
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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.
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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).