Nostr Web Client

Disclosure of hindered block propagation due to mutated blocks

Before Bitcoin Core v25.0, a peer sending mutated blocks could clear the

download state of other peers that also announced the block to us, which would

hinder block propagation.

This issue is considered Medium severity.

Details

Bitcoin Core treats a block as mutated when, for example, the Merkle root in the

header or the witness commitment in the coinbase transaction doesn’t match the

transactions in the block.

Before Bitcoin Core v25.0, a peer could clear the block download state of

other peers by sending an unrequested mutated block. This was a problem for, for

example, compact block relay. After receiving a compact block and while waiting

for a response to a getblocktxn request to reconstruct the full block,

receiving the mutated block would let Bitcoin Core forget about the compact

block reconstruction state. A blocktxn response arriving after the mutated

block couldn’t be used to reconstruct the block. This hindered block propagation.

This was fixed in #27608 by

making sure that a peer can only affect its own block download state and not the

download state of other peers.

Attribution

Credit goes to Suhas Daftuar for noticing the problem and working on a fix.

Timeline

2023-05-08 - A problem with mutated blocks is first reported in the #bitcoin-core-dev IRC channel.

2023-05-10 - Fix is merged (#27608)

2023-05-25 - v25.0 is released

2024-10-09 - Public disclosure