Decent - Eeyore's results

Lines of code

https://github.com/decentxyz/decent-bridge/blob/7f90fd4489551b69c20d11eeecb17a3f564afb18/src/DcntEth.sol#L20

Vulnerability details

The setRouter() function should only be called by the owner of the DcntEth contract. However, the onlyOwner() modifier is missing, and access is not restricted, allowing anyone to change the router address and consequently mint any amount of DcntEth tokens.

Impact

All WETH and ETH stored in the DecentEthRouter contract can be extracted by redeeming DcntEth tokens for WETH or ETH from it.

Proof of Concept

1. A malicious user utilizes the setRouter() function to update the router to an address they control.
2. Leveraging the mint() function with the onlyRouter() access control modifier, the attacker mints the desired amount of DcntEth tokens.
3. By employing the redeemEth() and redeemWeth() functions in the DecentEthRouter contract, the attacker extracts all ETH and WETH from it.
4. The attacker repeats the attack on all chains.

Recommended Mitigation Steps

Update setRouter() function with onlyOwner() modifier in the DcntEth contract.

-   function setRouter(address _router) public {
+   function setRouter(address _router) public onlyOwner {

Assessed type

Access Control

Lines of code

https://github.com/decentxyz/decent-bridge/blob/7f90fd4489551b69c20d11eeecb17a3f564afb18/src/DecentEthRouter.sol#L105 https://github.com/decentxyz/decent-bridge/blob/7f90fd4489551b69c20d11eeecb17a3f564afb18/src/DecentEthRouter.sol#L245 https://github.com/decentxyz/decent-bridge/blob/7f90fd4489551b69c20d11eeecb17a3f564afb18/src/DecentEthRouter.sol#L280 https://github.com/decentxyz/decent-bridge/blob/7f90fd4489551b69c20d11eeecb17a3f564afb18/src/DecentBridgeExecutor.sol#L36 https://github.com/decentxyz/decent-bridge/blob/7f90fd4489551b69c20d11eeecb17a3f564afb18/src/DecentBridgeExecutor.sol#L44 https://github.com/decentxyz/decent-bridge/blob/7f90fd4489551b69c20d11eeecb17a3f564afb18/src/DecentBridgeExecutor.sol#L63

Vulnerability details

When the bridge operation is initiated, the _from address is encoded from msg.sender, which can be the DecentBridgeAdapter contract address on the source chain.

In a situation where, on the destination chain, if the bridged msgType was MT_ETH_TRANSFER_WITH_PAYLOAD, a scenario can occur where, during the execution of the execute() function of the DecentBridgeExecutor contract, the .call() low-level function will revert for any reason, causing the DecentBridgeExecutor contract to refund the bridged funds back to the _from address.

Impact

In a case where the Decent protocol has no access to the _from address (due to different deployment addresses with no way to deploy to it), the funds will be locked.

Proof of Concept

1. A user bridges WETH to the destination chain with the swap payload for the destination chain to be performed with a low slippage setting.
2. The DecentBridgeAdapter contract on the destination chain is deployed on a different address than on the source chain.
3. In the _executeWeth() function, the target.call(callPayload) low-level call is made to the DecentBridgeAdapter destination chain contract.
4. The transaction is reverted in a situation where the desired swap is not performed due to a change in price.
5. Funds in the DecentBridgeExecutor are refunded to the _from address that the Decent protocol has no control over, resulting in the funds being locked.

Recommended Mitigation Steps

The _from address should be predefined by the Owner on each chain for each destination chain, so that the refund is made to the addresses controlled by the Decent protocol and from there to the original user.

Assessed type

Other

Lines of code

https://github.com/code-423n4/2024-01-decent/blob/main/src/UTB.sol#L115 https://github.com/code-423n4/2024-01-decent/blob/main/src/UTB.sol#L317

Vulnerability details

It is stated in the documentation that the protocol charges fees for transactions that require a bridge or a swap. In UTB contract those are swapAndExecute() and bridgeAndExecute().

As there is no access control protection, any user can use receiveFromBridge() function as a replacement for the swapAndExecute() function without the need to pay any fees.

Impact

The protocol will collect fewer fees than expected.

Proof of Concept

1. User uses swap instructions created for swapAndExecute() function and uses them in the receiveFromBridge() function.

Recommended Mitigation Steps

Add access control mechanism to receiveFromBridge() as it is intended to be used only when called by the BridgeAdapter.

Assessed type

Access Control