Blessed Wallbleed, the Leaky Wall

Patron of national firewalls, injected DNS responses, and walls with cracks.

Life

In February 2025, at the NDSS conference, a group of researchers presented Wallbleed: a flaw in the DNS injector of China's Great Firewall that, when answering certain malformed queries, appended up to 125 bytes of its own memory to the response. By watching it for years, the authors learned things about the inner workings of the digital wall. Even the highest walls sometimes let something seep through.

Prayer

O Blessed Wallbleed, wall that talks about itself, remind us that every parser, however mighty, must check its lengths. Amen.

How to celebrate

Celebrated by reading the paper and, in our own small way, checking buffer bounds.

High wall, small crack, big secret.