FlashLoopAdapter: Fake Safe Contract Bypasses Caller Authentication to Drain 114 ETH from Aave-Linked Wallets

A third-party Aave v3 Safe-module adapter authenticated the calling contract by asking the caller itself whether the module was enabled — an easy-to-spoof check. On October 1, 2026, an attacker deployed a malicious Safe that always returned `true`, then used a Morpho flash loan to repay Aave debt and withdraw collateral from two victim wallets for a net profit of ~114 ETH (~$305K).

Root Cause

The FlashLoopAdapter's open() and close() functions implemented caller authentication by calling back to msg.sender:

// Reconstructed vulnerable authentication pattern
function open(/* params */) external {
    // BUG: authentication is performed by asking the CALLER
    require(
        IGnosisSafe(msg.sender).isModuleEnabled(address(this)),
        "Module not enabled"
    );
    // ... proceed with Aave debt management
    _swap(/* caller-supplied router, calldata */);
}

Because the check relies solely on msg.sender.isModuleEnabled(address(this)), any contract that implements isModuleEnabled() returning true passes the authentication. The adapter had no whitelist of known Safe deployments and no on-chain registry check. Additionally, the _swap() helper accepted a caller-specified router address and arbitrary calldata, amplifying the blast radius.

Aave v3 itself was not affected; the vulnerability was entirely within the third-party adapter logic.

Attack Steps

Step	Action
1	Attacker deploys a malicious contract with `isModuleEnabled()` hard-coded to return `true`
2	Calls `open()` or `close()` on `FlashLoopAdapter` from the malicious contract
3	Authentication check passes — adapter proceeds as if caller is a legitimate Gnosis Safe
4	Attacker uses a Morpho flash loan to source ~1,335 WETH
5	Flash loan proceeds repay the Aave v3 debt position of the targeted Safe wallets
6	With debt cleared, the adapter's collateral-withdrawal path executes, extracting ~1,306 weETH
7	Flash loan repaid; attacker nets ~~114 ETH (~~$305K) across two victim wallets

Impact

Loss: ~$305,000 (approximately 114 ETH net profit)
Victims: Two Aave-linked Gnosis Safe wallets on Ethereum mainnet
Aave v3: Confirmed unaffected by Aave founder Stani Kulechov; core Aave pools were not accessed
Detection: SlowMist and Defimon Alerts both flagged the anomalous flash-loan flow shortly after execution

Lessons for Auditors

Never authenticate by interrogating the caller. Any authentication check that calls back to msg.sender to ask "are you authorized?" is trivially defeated by a malicious implementation. Authentication must be performed against an immutable registry or a pre-approved allowlist stored in the contract itself.
Restrict external swap routers. Allowing callers to specify arbitrary router addresses and calldata turns any DeFi integration into a potential drain vector. Use a hardcoded or governance-gated whitelist of approved routers.
Audit integration-layer contracts with the same rigour as core protocols. Third-party adapters that interact with high-value positions (Aave collateral, Gnosis Safe wallets) are first-class attack surfaces regardless of whether the underlying protocol is audited.
Flash loans do not add risk — but they remove capital barriers. This exploit required no upfront capital; any attacker with gas can repeat it. Protections must not assume the attacker lacks funds.