Sepolia Incident | Ethereum Foundation Blog

This weblog put up discloses a risk towards the Ethereum community that was current from the Merge up till the Dencun laborious fork.

Background

Previous to the merge, completely different message measurement limits for RPC communication have been set to guard shoppers from denial-of-service (DOS) assaults. These limits, utilized to messages obtained by way of HTTP endpoints, have been carried over to the engine API, which performs an important position in connecting Execution and Consensus Layer shoppers throughout block manufacturing. As a result of engine API’s involvement in block manufacturing, it turned doable for blocks to be produced that surpassed the RPC measurement limits of some shoppers however remained throughout the acceptable vary for others.

If an attacker creates a message that exceeds the dimensions restrict of the consumer with the bottom setting, whereas nonetheless adhering to the fuel restrict necessities, after which waits for a block to be produced, it might end in a state of affairs the place some shoppers regard the block as legitimate, whereas others reject it, issuing a HTTP error code “413: Content material Too Massive.”

Influence

An attacker that might craft these messages would be capable of power nearly all of nodes (=geth) to reject blocks {that a} minority would settle for. These blocks can 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 through the use of builders or a modified model of a consumer. Geth has a builtin restrict of 128KB for transactions, which signifies that a giant transaction just like the one beneath 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 the next restrict suggest the block and the CL requesting validation of this proposed greater block.

We proposed an answer in briefly decreasing the RPC restrict on all shoppers to the bottom worth (5MB). This could make the block invalid and an attacker can be very restricted within the chaos they will trigger within the community because the majority of the nodes would reject their blocks.

Nevertheless 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 fuel.

It is a greater situation 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 nearly all of the community, leading to quite a lot of forks (all being deemed legitimate by the minority nodes) and the chain retains reorging again and again.

Afterward February seventh, we got here to the conclusion that everybody elevating their RPC limits can be the safer different.

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 ought to be legitimate.
2024-02-06 15:14: Justin managed to place the transaction in a block and submitted it by way of the Besu consumer.
2024-02-06 20:46: Sam (EF) alerts Pari (particular because of 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 it
2024-02-07 23:40: We determined for all shoppers to restrict their RPC request restrict to 5MB
2024-02-07 6:40: We found that there is perhaps an even bigger situation and the assault might be executed with transactions lower than 128KB measurement.
2024-02-07 10:00: We determined for all shoppers to extend the RPC request restrict.
2024-02-07 21:00: The repair was merged in geth.
2024-02-09: Geth was launched