Second MEV Bot Falls to Its Own Tactics, Losing $2M in a Curve Sandwich

An MEV bot that made its living sandwiching other traders got sandwiched itself on Tuesday night, losing roughly $2 million in the process.

Researcher Spreek first flagged the incident, tracing it back to an unprotected swap function inside the bot's own code. The episode mirrors what happened to the notorious bot 0xbadc0de, which was rekt for $1.5M a year earlier. As was written at the time: "MEV bots act on the boundary of 'code is law'." It's difficult to muster much sympathy for an autonomous predator getting preyed upon in turn — call it another case of win some, lose some.

Credit for identifying the exploit goes to BlockSec, PeckShield, and Spreek.

Despite the intricate world MEV bots normally operate in, the mechanics behind this loss were straightforward. A public, unprotected swap function in the bot's contract — callable by anyone — allowed an attacker to sandwich the bot's own WETH/WBTC trades on Curve, financing the maneuver with a $50 million flash loan.

BlockSec described the mechanism:

A bot was attacked due to the lack of access control of a public function 0xf6ebebbb, which could be exploited to manipulate swaps in Curve pools. The loss was ~$2M.

Hence the attacker could first abuse the flawed function to pump the asset price (e.g., WETH) and then make a reverse swap to make a profit.

PeckShield separately published a breakdown of the sandwiched trades, and Spreek shared the final tally of the damage.

The attacker's address, funded via Tornado Cash, was 0x46d9b3dfbc163465ca9e306487cba60bc438f5a2. The attack itself ran through transaction 0xbc08860cd0a08289c41033bdc84b2bb2b0c54a51ceae59620ed9904384287a38, and the victim bot's address was 0x05f016765c6c601fd05a10dba1abe21a04f924a5.

As is often the case when large sums move through DeFi, Curve itself came out ahead. The trading volume needed to skew the pool enough to make the exploit viable generated roughly $250,000 in fees for the protocol. Meanwhile 0xc0ffeebabe — a bot better known for occasionally front-running exploits to whitehat them — also showed up to help tidy up the aftermath.

Controversial as they remain, autonomous MEV bots look increasingly like an unavoidable feature of a permissionless financial system, especially given the generous tips they route to validators. That arrangement keeps much of the ecosystem willing to tolerate the Dark Forest's more dangerous inhabitants — right up until one of those inhabitants becomes the prey.