Mellow Flexible Vaults — native token withdrawals permanently bricked

Source & credit. Reproduction of a public audit finding curated by AuditVault — the original finding: 62108-h-3-unable-to-withdraw-native-tokens-because-vault-and-redee. Standalone Foundry PoC and full write-up: 62108-h-3-unable-to-withdraw-native-tokens-because-vault-and-redee_exp in the evm-hack-registry mirror.

Vulnerability classes: vuln/dos/frozen-funds · locked-funds · known-pattern

Reproduction: self-contained Foundry PoC with only forge-std. Full trace: output.txt. PoC: test/62108-h-3-unable-to-withdraw-native-tokens-because-vault-and-redee_exp.sol.

AuditVault taxonomy: severity/high · sector/staking · sector/token · platform/sherlock · locked-funds · reentrancy-guard

Key info#


Impact	HIGH — native-asset withdraw path always reverts; deposits stuck
Protocol	Mellow Flexible Vaults ShareModule / BasicRedeemHook
Vulnerable code	`getLiquidAssets` uses `IERC20(asset).balanceOf` for all assets
Bug class	Missing native-token branch
Finding	Sherlock 2025-07-mellow-flexible-vaults · #62108 · H-3
Report	sherlock-audit/2025-07-mellow-flexible-vaults-judging
Source	AuditVault
Status	Fixed by protocol (PR #10). Reproduced as standalone local PoC.
Compiler	`^0.8.24` (PoC)

TL;DR#

Protocol lists native token (0xEeee…eEEeE) as a supported asset.
Liquid-asset queries always call ERC20 balanceOf on the asset address.
Native sentinel has no code → call reverts → redeem processing is impossible.

The vulnerable code#

SOLIDITY

function getLiquidAssets() public view returns (uint256) {
    return hook == address(0)
        ? IERC20(asset).balanceOf(address(this)) // @> VULN
        : IRedeemHook(hook).getLiquidAssets(asset);
    // FIX: if (asset == NATIVE) return address(this).balance;
}

Root cause#

Native ETH is not an ERC20. Using balanceOf on the sentinel address reverts, so both the no-hook path and BasicRedeemHook break for native vaults.

Attack walkthrough / harm demo#

Configure vault asset = native sentinel; deposit ETH.
Redeem queue calls vault.getLiquidAssets() → revert.
processWithdraw cannot complete; funds cannot leave via the redeem path.

Diagrams#

flowchart TD A["RedeemQueue needs liquid assets"] --> B["Vault.getLiquidAssets"] B --> C{"asset == NATIVE?"} C -->|"no branch exists"| D["IERC20.balanceOf on 0xEeee"] D --> E["REVERT — withdraw bricked"] C -->|"FIX"| F["return address this balance"]

Impact#

Any vault using native ETH as the asset cannot process redemptions. Deposited native value is stuck from the protocol's withdraw path (admin rescue aside).

Sources#

AuditVault finding #62108
Sherlock issue #147
Reduced source: ShareModule.sol / BasicRedeemHook.sol @ eca8836

Sources & further analysis#

Reproductions & code

Standalone PoC + full trace: 62108-h-3-unable-to-withdraw-native-tokens-because-vault-and-redee_exp (evm-hack-registry mirror).
AuditVault finding: 62108-h-3-unable-to-withdraw-native-tokens-because-vault-and-redee.

Alerts & third-party analyses

Web3Sec X hacked database: search.
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Solodit incident search: search.

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