Rucknium discovers critical privacy vulnerability in Wownero's decoy selection algorithm

MRL¹’s Rucknium² has discovered³ a critical privacy vulnerability in Wownero⁴’s decoy selection algorithm after performing a simple empirical analysis of the blockchain data.

It apparently affects the current version (0.11.2.0)⁵ of wownero-wallet-cli, wownero-wallet-rpc and the majority of non-mining transactions confirmed on Wownero’s blockchain since approximately September 27, 2022:

An observer of the blockchain can deduce the real spend of these transactions (i.e. construct the true transaction graph) with nearly 100% confidence. [..] the real spend can be deduced by a blockchain observer for about 80 percent of rings confirmed on the blockchain since September, 27, 2022

The researcher suggested the appropriate fix would be to properly set the temporal anchor for the decoy selection algorithm to the most recent block with spendable outputs (i.e. after the ten block lock).

WOW maintainer jwinterm⁶ asked⁷ testers to check and report on the state of other wallet implementations and invited contributors to submit a patch.

Read WOW issue #488³ and join #monero-community discussions⁸ to learn more about this story.

This is an ongoing story and the report will be updated when new information is available.

Update: PR with potential fix submitted by wowario thanks to jeffro256’s suggestion⁹.