More than 1,900 ETH were stolen, and how Radiant Capital was hacked to steal $4.5 million

On January 3, 2024, the Radiant Capital project suffered a flash loan attack by an attacker. The attacker stole more than 1,900 ETH through 3 transactions, worth more than 4.5 million US dollars. The stolen funds are currently still stored at the attacker’s address.

Written by: Beosin

On January 3, 2024, according to monitoring by Beosin’s EagleEye security risk monitoring, early warning and blocking platform, the **Radiant Capital project suffered a flash loan attack from an attacker. The attacker stole more than 1,900 ETH, worth more than 4.5 million US dollars, through 3 transactions. The stolen funds are still stored at the attacker’s address. **Beosin security team analyzed this incident immediately.

Vulnerability analysis

The root cause of this incident is that the Radiant Capital project used precision expansion and rounding in the process of calculating the number of tokens, allowing attackers to expand profits by controlling the precision and combining rounding. Click to attack. **

Observing the above code, the rayDiv function passes in two uint256 data a and b. The whole process can be abbreviated as (a*RAY+b/2)/b, where RAY is the precision extended data, which is 10^27, so the result is quite At a*RAY/b+0.5, the rounding function is implemented, and the error of this calculation method mainly comes from b. If b is extremely small relative to a, then the error will be negligible, but if b has the same order of magnitude as a , then the error may reach a itself.

For example: if a*RAY=10000, b=3, then the calculated result is 3333, which is 1/10000 smaller than the actual value; and if a*RAY=10000, b=3000, the calculated result is 3, 1/10 smaller than the actual value.

In this incident, the attacker manipulated the value of b so that the value of b and the value of a have the same order of magnitude, making the calculation equivalent to 3/2.0001=1, and the calculated value is 1/3 smaller than the actual value.

Attack process

Let’s take a look at the hacker’s attack process:

1. The attacker first borrowed 3 million USDC through AAVE flash loan, which was used to fund the attack.

2. The attacker pledged 2 million USDC to the Radiant contract and obtained 2 million rUSDCn certificate tokens.

3. The attacker performs a flash loan through the Radiant contract, borrows 2 million USDC, returns the 2 million USDC in the callback function, and extracts the USDC pledged in the second step. Finally, the flash loan function will call the transferfrom function with interest. Transfer the attacker’s USDC into the contract. **At this time, a handling fee of 9/10000 will be charged, and the handling fee collected becomes the liquidity of the pool. **

4. By repeating step 3 many times, the attacker controls the liquidityIndex to be very large, liquidityIndex=271800000000999999999999998631966035920.

5. Next, the attacker creates a new contract and puts 543,600 USDC into it, **because 5436 (USDC value) is exactly twice the 2718 (liquidityIndex value) in step 4, which can be easily controlled by rounding. **

6. The attacker mortgaged all 543,600 USDC into the Radiant contract and obtained the same amount of rUSDCn.

7. The attacker extracted 407,700 USDC, which should have destroyed 407,700 rUSDCn, but as mentioned above, the burn function performed precision expansion and rounding calculations.

40770000000000000000000000000000000000/271800000000999999999999998631966035920=1.49999999, and the rounding result is 1, causing the result to be 1/3 smaller.

As shown in the picture below, 407,700 USDC should have been destroyed, but 271,800 were left, indicating that only 271,800 were destroyed, and the attacker withdrew 407,700 USDC.

8. The attacker exploits the vulnerability in step 7 to repeat the pledge withdrawal operation, and the withdrawal is always 1/3 more than the pledge amount, and finally exchanges all the USDC in the pool. **

Fund Tracking

As of press time, the 1,902 ETH stolen have been stored in the hacker’s address and have not been moved. Beosin Trace will continue to monitor the funds. **

As 2024 begins, we have already witnessed two cases of large-scale thefts. (Review of yesterday’s security incidents: What happened to the first case of the year, the $80 million stolen Orbit Chain incident?) This series of events once again reminds us that in the Web3 ecosystem, security precautions are still Very important! **