The anonymity focused Monero cryptocurrency with a market cap of some $3.5 billion seems to be under attack following an asics hardfork which wiped out much of their hashrate.
“There was one fork that reorganized by an astonishing 21 blocks. That means the eventually-thrown-away branch was the longest one for 21 blocks before the “other” branch (which eventually became the winner) overtook it. A 21-block branch is enough to double-spend against basically anybody.
2018-05-06 20:13:35.002 [P2P5] INFO global src/cryptonote_core/blockchain.cpp:934 REORGANIZE SUCCESS! on height: 1565690, new blockchain size: 1565711″
So says an apparent Monero user. Riccardo Spagni, a Monero dev, said “His reorg is dated yesterday, but it’s a section of blocks from 2.6 days ago, so DEFINITELY a reorg during catch up. Nobody else has seen anything besides a reorg of a single block or two, and http://xmr.to has been down for unrelated reasons. Much ado about nothing.”
There have been at least two public reports of double spend attacks. “2 days ago I send first out transaction, but something went wrong and above 24 hours balance was 0. XMR returned, but now I cannot send them,” one of them says.
The other one says: “I am struggling to send my balance of XMR to another wallet. I have tried both GUI and CLI and everytime I get an error that suggests I am trying to double spend.”
Spagni said these sudden complaints of double spends are “probably because they’re using a remote node or something weird.”
It’s unclear however at this stage what is going on, if anything, but a number of apparent Monero users paint a picture of a network under attack.
“A lot of weird stuff happened on mainnet in the past 48h… My public node stopped syncing and got corrupted tx-pool. Up to 10 of our pool leaf nodes stopped syncing several times as well,” one of them says.
“My miners and node have been DDoS’d like crazy the past couple weeks… I believe Dwarfpool has been affected, deeply, by this whole shabang. Haven’t gotten a payout in a couple days and hashrate dropped for ‘no reason,'” says another.
We can not confirm these claims at this stage, but they are made just a month after Monero hardforked to get rid of asics, which dropped its hashpower, and thus arguably security, by some 80%, to then slightly recover.
As can be seen above, the hashrate has not increased much for about 2-3 weeks, so if there is an intentional double spend attack it would not be coming from the outside, although after the hashrate plunged it did initially double.
It may well be there is some misconfiguration somewhere, or perhaps even a bug in the new fork code that went out last month, but as stated Monero’s dev has said there isn’t anything unexpected on-going.
A 21 blocks deep re-organization of the blockchain would mean that all transactions within those 21 blocks are effectively discarded in one chain, but are valid in the other.
It is effectively a chain-split, but for a relatively short period of 21 blocks. That could mean transactions can be replayed, or an attacking miner or perhaps a rogue employee within the miner could double spend his own transactions.
Spagni has stated he has not seen more than two block deep re-orgs, or rollbacks, but some users are complaining of double spending. Therefore it is unclear at this stage just what exactly is going on.