As an example I investigated, to put a custom domain in front of a B2 bucket they suggest using Cloudflare and CNAME-ing a bucket subdomain (eg f000.backblazeb2.com) https://www.backblaze.com/docs/cloud-storage-deliver-public-...
Well if f000.backblazeb2.com is used for any other people's buckets too, which appears to be the case, I guess I am now able to serve other people's files from my domain? This seems terrible.