Tavis Ormandy (Tavis Ormandy) of Google’s Project Zero uncovered a major vulnerability in the Cloudflare Internet infrastructure service. Essentially, web requests to Cloudflare-backed sites received answers which included random information from other Cloudflare-backed sites!
This information could potentially include confidential information (private messages on dating sites, emails), user identity information (Personally Identifying Information (PII), and potentially in a healthcare context, Protected Health Information (PHI), or user, application, or device credentials (passwords, API keys, authentication tokens, etc.)
Both Project Zero and Cloudflare acted promptly. The bug was reported on 2017–02–17 and a mitigation was in place within an hour. Public notification was given on 2017–02–23.