TL;DR Some hosting providers implemented http-01 having one part of the challenge key reflected in the response. This resulted in a huge amount of websites being vulnerable to XSS just because of their implementation of the http-01 ACME-challenge.

TL;DR Bucket upload policies are a convenient way to upload data to a bucket directly from the client. Going through the rules in upload policies and the logic related to some file-access scenarios we show how full bucket object listings were exposed with the ability to also modify or delete existing files in the bucket.