This weblog publish discloses a menace in opposition to the Ethereum community that was current from the Merge up till the Dencun exhausting fork.
Background
Previous to the merge, totally different message dimension limits for RPC communication have been set to guard purchasers from denial-of-service (DOS) assaults. These limits, utilized to messages obtained through HTTP endpoints, have been carried over to the engine API, which performs an important function in connecting Execution and Consensus Layer purchasers throughout block manufacturing. Because of the engine API’s involvement in block manufacturing, it grew to become doable for blocks to be produced that surpassed the RPC dimension limits of some purchasers however remained inside the acceptable vary for others.
If an attacker creates a message that exceeds the scale restrict of the consumer with the bottom setting, whereas nonetheless adhering to the gasoline restrict necessities, after which waits for a block to be produced, it might end in a scenario the place some purchasers regard the block as legitimate, whereas others reject it, issuing a HTTP error code “413: Content material Too Giant.”
Influence
An attacker that might craft these messages would be capable of drive the vast majority of nodes (=geth) to reject blocks {that a} minority would settle for. These blocks could be forked away and the proposer would miss out on rewards.
To start with we thought that it was solely doable to create these blocks by utilizing builders or a modified model of a consumer. Geth has a builtin restrict of 128KB for transactions, which implies that a giant transaction just like the one below dialogue wouldn’t find yourself within the transaction swimming pools of any geth node. It was nonetheless doable to nonetheless set off the restrict by having a consumer with a better restrict suggest the block and the CL requesting validation of this proposed larger block.
We proposed an answer in briefly reducing the RPC restrict on all purchasers to the bottom worth (5MB). This may make the block invalid and an attacker could be very restricted within the chaos they’ll trigger within the community because the majority of the nodes would reject their blocks.
Nonetheless on February seventh we found that it was doable to create a block that might hit the 5MB restrict with a bunch of transactions which might be under the 128KB restrict and never exceed 30 million gasoline.
This can be a larger challenge as a result of we realized an attacker might create a bunch of excessive paying transactions and ship them to the community. Since he outpays everybody else within the mempool, each node (even geth nodes) would come with the assault transactions of their block thus making a block that might not be accepted by the vast majority of the community, leading to loads of forks (all being deemed legitimate by the minority nodes) and the chain retains reorging over and over.
In a while February seventh, we got here to the conclusion that everybody elevating their RPC limits could be the safer various.
Timeline
2024-02-06 13:00: Toni (EF), Pari (EF) and Justin (Besu) attempt to submit a specificly grinded transaction to the community. The transaction contributes to as much as 2.7 MB blocks when snappy compressed.2024-02-06 13:25: Pari receives errors from his native Geth node though the transaction needs to be legitimate.2024-02-06 15:14: Justin managed to place the transaction in a block and submitted it by the Besu consumer.2024-02-06 20:46: Sam (EF) alerts Pari (particular due to mysticryuujin on X), Toni and Alex about sure Sepolia nodes struggeling.2024-02-06 21:05: Staff double checks with Marius from Geth and confirms the bug.2024-02-06 21:10: The gang will get collectively to debug it2024-02-07 23:40: We determined for all purchasers to restrict their RPC request restrict to 5MB2024-02-07 6:40: We found that there is likely to be a much bigger challenge and the assault will be executed with transactions lower than 128KB dimension.2024-02-07 10:00: We determined for all purchasers to extend the RPC request restrict.2024-02-07 21:00: The repair was merged in geth.2024-02-09: Geth was launched
Whereas Geth was the one consumer affected by this bug, different purchasers have additionally up to date their defaults to be secure of this assault even when gasoline limits are elevated.
The consumer groups indicated that the next updates have the secure rpc limits:
Geth: v1.13.12
Nethermind: v1.25.4
Besu: 24.1.2
Erigon: v2.58.0
Reth: v0.1.0-alpha.18
