  Ethereum prospered the inception of a plethora of smart contract
applications, ranging from gambling games to decentralized finance. However,
Ethereum is also considered a highly adversarial environment, where vulnerable
smart contracts will eventually be exploited. Recently, Ethereum's pool of
pending transaction has become a far more aggressive environment. In the hope
of making some profit, attackers continuously monitor the transaction pool and
try to front-run their victims' transactions by either displacing or
suppressing them, or strategically inserting their transactions. This paper
aims to shed some light into what is known as a dark forest and uncover these
predators' actions. We present a methodology to efficiently measure the three
types of frontrunning: displacement, insertion, and suppression. We perform a
large-scale analysis on more than 11M blocks and identify almost 200K attacks
with an accumulated profit of 18.41M USD for the attackers, providing evidence
that frontrunning is both, lucrative and a prevalent issue.
