So tptacek's comment summarizes it well:

| Oh, my god.
|
| Read the whole event log.
|
| If you were behind Cloudflare and it was proxying sensitive data
| (the contents of HTTP POSTs, &c), they've potentially been spraying
| it into caches all across the Internet; it was so bad that Tavis
| found it by accident just looking through Google search results.
|
| The crazy thing here is that the Project Zero people were joking
| last night about a disclosure that was going to keep everyone at
| work late today. And, this morning, Google announced the SHA-1
| collision, which everyone (including the insiders who leaked that
| the SHA-1 collision was coming) thought was the big announcement.
|
| Nope. A SHA-1 collision, it turns out, is the minor security news
| of the day.
|
| This is approximately as bad as it ever gets. A significant number
| of companies probably need to compose customer notifications; it's,
| at this point, very difficult to rule out unauthorized disclosure
| of anything that traversed Cloudflare.

https://news.ycombinator.com/item?id=13718752