Pierluigi Paganini November 13, 2020

Threat actors have stolen $2 million worth of Dai cryptocurrency from the cryptocurrency borrowing and lending service Akropolis.

Cryptocurrency borrowing and lending service Akropolis disclosed a “flash loan” attack, hackers have stolen roughly $2 million worth of Dai cryptocurrency.

The attack took place on November 12, in response to the attack the platform halted all the transactions to prevent hackers from stealing further funds.

The company immediately launched an investigation into the incident with the help of two forensics firms. The experts determined that the platform was hit with a “flash loan” attack.

Below the results of the investigation published by the company:

“There exist two bugs related to the Deposit flow:

1. No check that tokens deposited are actually the ones registered in our contracts
2. Re-entrance issue with “transferFrom” function which an attacker was able to exploit because of first bug”

Below the attack flow:

• The hacker created a flash-loan to borrow funds then called SavingsModule.deposit() with fake token (his own contract 0xe2307837524db8961c4541f943598654240bd62f)
• During “transferFrom” of this fake token, he executed another deposit with real 800k DAI borrowed from DyDx.
• The balance of the pool was actually increased during the first deposit and as a result our PoolTokens were minted twice.
• Thus he was able to withdraw almost double amount.

A Flash loan attack takes place when hackers loan funds from a DeFi platform and bypass the loan mechanism to steal funds using exploits.

Since February, researchers observed a growing number of load attacks, in October, a hacker stole approximately $24 million worth of cryptocurrency assets from decentralized finance service Harvest Finance,

According to the advisory, the stolen funds are currently held in the Ethereum wallet 0x9f26ae5cd245bfeeb5926d61497550f79d9c6c1c.

Akropolis notified major cryptocurrency exchanges about the attack and it is working to freeze the Ethereum account where the funds are stored.

The company announced it is planning to reimburse its users.

Pierluigi Paganini

(SecurityAffairs – hacking, Akropolis)

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