This leak (a bit referred to as #cloudbleed) is extensively covered in the following posts.
- Cloudflare - Incident report on memory leak caused by Cloudflare parser bug
- ARS Techinca - Serious Cloudflare bug exposed a potpourri of secret customer data
- Chromium Bug Tracker - Cloudflare Reverse Proxies are Dumping Uninitialized Memory
- Pirate (GitHub) - List of Sites possibly affected by Cloudflare's #Cloudbleed HTTPS Traffic Leak