At the Breaking Bitcoin Conference in Paris last weekend, speakers from around the world gave talks about breaking down the technicals of different implementations such as Segwit2x, Bitcoin Unlimited, and IOTA.
The most controversial talk was given by alternative Bitcoin implementation developer, Christopher Jeffrey, who revealed to a live audience of about 200 developers, academics, and professionals in the Bitcoin space how he broke the default Bitcoin implementation, bitcoind, better known as Bitcoin Core.
He drove the point home that the software ecosystem in the Bitcoin protocol is glaringly centralized. While Reddit and Twitter conversations focus on the threat to decentralization that miners pose to Bitcoin, Jeffrey highlighted a less popular, though equally harrowing threat: development centralization.
More than 99% of the Bitcoin network today runs Bitcoin Core, which is the default software implementation served by the package managers in most major operating systems. Jeffrey drove this point home by giving a poignant live demonstration.
Opening his talk, Pitfalls of Consensus Implementation, Jeffrey demonstrated a denial-of-service (DoS) attack by running a script which caused bitcoind nodes to allocate excessive amounts of memory, causing them to grind to a halt. This was a successful out-of-memory (OOM) attack executed in the Bitcoin testnet.
This OOM attack on Bitcoin Core, dubbed Corebleed, focuses on machine details, abusing memory, CPU, and disk I/O bottlenecks. This, combined with targeting the consensus layer, “which cannot be ignored by nodes,” Jeffrey notes, would break Bitcoin by bricking the nodes that were running Core software.
Theoretically, if this denial-of-service (DoS) vector were exploited in mainnet, it would shut down a significant portion of the nodes running Bitcoin. Only those nodes backed by beefy servers could survive this attack. However, Jeffrey claims that this would take months to set up.
There are two versions of this attack: a miner version and a non-miner version. The miner version remains strictly theoretica, simply because it is cost prohibitive to execute.