RsETHSafeModule exploit analysis

A Gnosis Safe that had enabled a private DeFi-Saver-style module lost 2,900 aEthrsETH on 2026-09-15, worth ~$7.8M gross, after an unprivileged contract reached the enabled module through a self-referential multicall on the Router (example exploit transaction, block 25980525). DeFiHackLabs reconstructs the authorization bypass against the live Router, module, RecipeExecutor and victim Safe at the parent block.

The Router exposes multicall(address _contract, bytes[] _data). It gates the call on the target, and _isAuthorized returns true whenever _contract == address(this). An unauthorized caller can therefore wrap the whole thing in multicall(ROUTER, [ ... ]): the outer call passes because the target is the Router itself, and the payload then runs with the Router's own trusted identity as msg.sender. The nested payload is a second multicall(MODULE, [ moduleCall ]) and the enabled Safe module trusts the Router as caller, so it forwards execTransactionFromModuleReturnData(RecipeExecutor, 0, executeRecipe(...), 1) into the victim Safe with operation = 1 (DELEGATECALL). The recipe, delegatecalled in the Safe's context, moves the Safe's aEthrsETH into a pre-positioned Uniswap V4 pool the frontrunner had set up to sweep it to rsETH.

The example tx is the MEV frontrunner's; two "exploiter" addresses that appear in later blocks are losing copycats. DeFiHackLabs records a gross victim loss of 2,900 aEthrsETH (~$7.8M) and the frontrunner's net profit of 2,882.37 rsETH (~$7.73M) after the ~17.63 rsETH the frontrunner swapped to ETH for the builder.

The cleanest fix is to drop the _contract == address(this) short-circuit in _isAuthorized and reject self-referential multicall entirely; calling multicall(MODULE, ...) directly from an unprivileged address reverts, as DeFiHackLabs confirms in its negative control.