blockedAddrs can bypass

[c4-bot-6]

Lines of code

https://github.com/code-423n4/2024-05-canto/blob/d1d51b2293d4689f467b8b1c82bba84f8f7ea008/canto-main/x/coinswap/keeper/msg_server.go#L144 https://github.com/code-423n4/2024-05-canto/blob/d1d51b2293d4689f467b8b1c82bba84f8f7ea008/canto-main/x/onboarding/keeper/ibc_callbacks.go#L96

Vulnerability details

Impact

Bypass the blacklist

Proof of Concept

coinswap module SwapCoin function to validate the input parameters Then call Swap function, and then call TradeInputForExactOutput/TradeExactInputForOutput

SwapCoin -> Input verification -> Swap -> TradeInputForExactOutput/TradeExactInputForOutput

However, the onboarding module's OnRecvPacket callback function directly calls the TradeInputForExactOutput function without verifying the input.

OnRecvPacket -> TradeInputForExactOutput

In this report let's look at the validation of blockedAddrs:

func (m msgServer) SwapCoin(goCtx context.Context, msg *types.MsgSwapOrder) (*types.MsgSwapCoinResponse, error) {
    ....
    if m.Keeper.blockedAddrs[msg.Output.Address] {
        return nil, errorsmod.Wrapf(sdkerrors.ErrUnauthorized, "%s is not allowed to receive external funds", msg.Output.Address)
    }
    ....
}

There is no verification of Output.Address in OnRecvPacket, so an attacker can bypass blockedAddrs detection using the onboarding module.

Tools Used

vscode, manual

Recommended Mitigation Steps

-    OnRecvPacket -> TradeInputForExactOutput
+    OnRecvPacket -> SwapCoin

Assessed type

Invalid Validation

[3docSec]

The onboarding module only swaps gas (very little) amounts, and it does it only once, so it's not clear how an H/M impact can be caused by this finding.

[c4-judge]

3docSec changed the severity to QA (Quality Assurance)

[c4-judge]

3docSec marked the issue as grade-b

[poorphd]

Send to blocked address is already handled by IBC transfer module. Once IBC transfer ack has error, coinswap logic doesn't initiate and we have test case for that. https://github.com/code-423n4/2024-05-canto/blob/main/canto-main/x/onboarding/ibc_module_test.go#L175-L191