By: Sissice
background
On April 24, 2024, according to the intelligence of the SlowMist security team, the YIEDL project on the BSC chain was attacked, and the attacker made a profit of about $300,000. The SlowMist security team analyzed the attack and shared the results as follows:
(https://twitter.com/SlowMist_Team/status/1782962346039898473)
Related Information
Attacker Address:
0x322696471792440499b1979e0a440491e870667a
Attacked contract address:
0x4edda16ab4f4cc46b160abc42763ba63885862a4
Some of the attack transactions:
0x49ca5e188c538b4f2efb45552f13309cc0dd1f3592eee54decfc9da54620c2ec
0x3629ad588ac120163792e92b6c43bd4bdc5bf35cac66eb7f3a0267df93abc849
0x0a89b8670c40b4067b9522a5933c3bf8c44c968103aa642b04c65d49ad9e6457
0x5e468cba495e5f6165418fb9d87d824309c54261055425f33f588dd3b3abbcea
0x8710034dadecfc8c26f651c612f613fffdece6e2f9957b9ec8ab843218168c1d
0x9da398ed274c8cfa774b36003fa8c930d3430d0fc5889b5008830fd6463f68a9
0x2e3d4332f66a334e0170187011ed673dc222f95bf4443b618e08f8052437ef7a
0x5a15fdc57c35f2305aaa0bb95b109ad412b17406d737d137190fe5867393339d
0x8ef3765665cd849cdf9132ab37caf6aa0f891e1f7d9f418f86a6ab6ea38b6f5b
0xa9fa04b033afbed2218679aea92e9429a5f7839d0b4c65358ebf9ba20efcd021
Attack the Core
The core of the attack in this incident was to exploit the failure to fully verify the external parameters input by the user when the contract processes the redeem function call. This parameter is the key data for controlling asset exchange and usually contains specific transaction instructions or routing information. The attacker maliciously constructed this external parameter to achieve unauthorized asset transfer.
Transaction Analysis
The attacker calls the redeem function multiple times to redeem an amount of 0 assets, which itself seems harmless because a redemption amount of zero usually does not trigger any actual fund flow:
However, following the redeem function, we can find that this function will traverse the list of assets allowed by the contract, and when the current asset is not the asset the user wants to receive, it will parse the passed dataList parameter and externally call the corresponding function in 1inch Router to perform the asset exchange operation.
Since the dataList passed in here has not been checked and verified, the attacker can construct malicious values to execute the unoswapTo function of the 1inch Router contract to perform any controllable token exchange operations.
As a result, the WBNB-ADA Token in the Yiedl BULL contract was exchanged for BNB to the attacker’s address.
In this way, the attacker can trigger the token exchange operation controlled by the dataList parameter without actually owning any redemption shares, and can mobilize contract funds multiple times and exit with profits without consuming their own assets.
Summarize
The core of this attack is that the function failed to fully verify the dataList parameter input by the user, allowing the attacker to construct malicious external data and use 1inch to siphon off the tokens in the contract. The SlowMist security team recommends that project owners implement a strict parameter verification mechanism during development, especially when it comes to fund operations in contracts, to ensure that all external calls comply with expected behavioral specifications, and conduct a thorough security audit of the contract logic to prevent similar incidents from happening again.
