AlpsCon AI Trade Hub: Reward-Checkpoint Bug + Stale EIP-7702 Whitelist Drain $152K

Two independent vulnerabilities combined to drain $152K USDC from AlpsCon AI Trade Hub on BNB Chain: a reward-accounting bug that left migrated positions' rewardDebt at zero (crediting pre-existing accumulated rewards), and a 14-month-old EIP-7702 whitelist entry for the Hardhat default account whose private key is publicly known.

Root Cause

AlpsCon's newer reward hub contracts use a MasterChef-style accRewardPerShare accounting model. When a staking position was migrated from an older hub, the new contract set the user's rewardDebt to zero instead of initialising it to amount × accRewardPerShare / PRECISION. This meant every migrated position was immediately owed all rewards that had accumulated since the hub's inception — a classic checkpoint-on-deposit bug.

Separately, the contract's EIP-7702 whitelist (used to gate certain privileged calls) still contained the Hardhat default account address (0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266) — a well-known key distributed in every Hardhat installation — which had been on the whitelist for approximately 14 months.

// Vulnerable MasterChef-style migration (reconstructed from Verichains analysis)
function migrateFromOldHub(address user, uint256 amount) external onlyOldHub {
    UserInfo storage info = userInfo[user];
    info.amount += amount;
    // BUG: should be: info.rewardDebt += amount * accRewardPerShare / PRECISION;
    // info.rewardDebt is left at 0 (or unchanged from prior deposits)
}

function harvest() external {
    UserInfo storage info = userInfo[msg.sender];
    uint256 pending =
        info.amount * accRewardPerShare / PRECISION - info.rewardDebt;
    // 'pending' is inflated for migrated positions
    _safeReward(msg.sender, pending);
    info.rewardDebt = info.amount * accRewardPerShare / PRECISION;
}

Attack Steps

#	Action
1	Attacker derives Hardhat default private key (publicly known)
2	Signs EIP-7702 authorization to pass the whitelist gate
3	Flash-borrows tokens; triggers migration from old hub → new hub
4	New position's `rewardDebt` initialised to 0
5	Calls `harvest()` → claims all rewards accumulated since hub deployment
6	Repays flash loan; nets ~$152,295 USDC

Impact

~$152,295 USDC drained from AlpsCon AI Trade Hub reward pool on BNB Chain
Two separate, independently exploitable vulnerabilities (whitelist + accounting)
Incident dated October 18, 2026 (SlowMist / Verichains)

Lessons for Auditors

Always set rewardDebt on every state change that affects amount. In MasterChef forks, rewardDebt must be updated atomically with every deposit, withdrawal, and migration: rewardDebt = amount * accRewardPerShare / PRECISION. Missing this on migration paths is one of the most common DeFi yield-farming bugs.
Purge test keys from production whitelists before deployment. The Hardhat default accounts (0xf39F..., 0x7099..., etc.) have publicly known private keys. Their presence in any production access-control list is a critical vulnerability. Run a pre-deployment check: grep -r '0xf39Fd6e51' contracts/ should return zero results in production builds.
EIP-7702 whitelists require periodic rotation audits. EIP-7702 authorization lists can accumulate stale entries. Implement an expiry mechanism or a regular (quarterly) review to prune addresses that no longer need privileged access.
Two low-severity findings can combine into a high-severity exploit. Neither bug alone may be rated critical, but the whitelist bypass enabling the accounting exploit produced a significant loss. Auditors should model compound exploit paths.