Wallbleed, a buffer over-read vulnerability that existed in the DNS injection subsystem of the Great Firewall of China. Wallbleed caused certain nation-wide censorship middleboxes to reveal up to 125 bytes of their memory when censoring a crafted DNS query. It afforded a rare insight into one of the Great Firewall’s well-known network attacks, namely DNS injection, in terms of its internal architecture and the censor’s operational behaviors.