Submitted by haxatron, also found by EV_om, MrPotatoMagic, deth, rouhsamad, Aamir, Topmark, and bart1e
When the DecentEthRouter receives the dcntEth OFT token from a cross-chain transaction, if the WETH balance of the destination router is less than amount of dcntEth received (this could be due to the router receiving more cross-chain transactions than than sending cross-chain transactions which depletes its WETH reserves), then the dcntEth will get transferred to the address specified by _to.
DecentEthRouter.sol#L266-L281
This dcntEth is sent to the user so that they can either redeem the WETH / ETH from the router once the WETH balance is refilled or send it back to the source chain to redeem back the WETH.
The problem is that if the msgType != MTETHTRANSFER, then the _to address is not the user, it is instead the target meant to be called by the destination chains bridge executor (if the source chain uses a decent bridge adapter, the target is always the destination chains bridge adapter which does not have a way to withdraw the dcntEth).
The following snippet shows what occurs in the bridge executor (_executeEth omitted as it does largely the same thing as _executeWeth):
DecentBridgeExecutor.sol#L24-L82
Therefore, once the dcntEth is transferred to the execution target (which is almost always the destination chain bridge adapter, see Appendix for the code walkthrough). The user cannot do anything to retrieve the dcntEth out of the execution target, so the cross-chain transaction is lost.
Pass a destination chain refund address into the payload sent cross-chain and replace the _to address used in DecentEthRouter.sol#L267:
wkantaros (Decent) confirmed but disagreed with severity
0xsomeone (Judge) commented:
