On February 27, 2026, Foom.cash faced a critical Smart Contract exploit across Ethereum and Base networks. The attack vector was a Groth16 Verifier deployment error, leading to a "Forged Proof" vulnerability. While $2.26M was initially at risk, a coordinated white-hat effort recovered 81% ($1.84M) of the funds.
This post deep-dives into the technical execution of that recovery.
The Vulnerability: Groth16 Malleability & Forged Proofs
The core of the issue lay in the Zero-Knowledge Proof (ZKP) verification logic. Specifically, the Groth16 verifier contract had a misconfiguration that failed to properly validate the constraints between public inputs and the proof.
- The Bug: The contract didn't strictly check if the proof was unique or if it was bound to the specific transaction data.
- The Exploit: Attackers used "Proof Malleability." By slightly altering a valid proof, they could generate a "new" forged proof that the contract still accepted as true.
- The Result: This allowed unauthorized withdraw() calls, tricking the contract into releasing funds to the attacker's address.
The Rescue Operation: "White-Hat Front-running"
The recovery wasn't just a patch; it was an active counter-exploit. Here is how @duha_real and DecurityHQ secured the funds:
Real-time Monitoring & Mempool Analysis
Security researcher @duha_real (a former Foom.cash hacking contest winner) detected the malicious transactions on the Base network. By performing a deep-dive analysis of the transaction's input data and the forged proof structure, he was able to reverse-engineer the exploit payload.
The "Save-to-Safe" Strategy
To prevent the attacker from draining the remaining TVL (Total Value Locked), the white-hats used the same forged proof vulnerability against the protocol:
1. **Scripting the Interception:** They deployed a script to submit withdrawal transactions with higher gas fees (priority fees) than the attacker.
2. Redirecting Funds: Instead of withdrawing to a personal wallet, the white-hats directed the output of the forged proofs to a Secure Multisig Wallet controlled by the recovery team.
3. Cross-chain Coordination: While @duha_real focused on Base, the security firm DecurityHQ executed a similar rescue on Ethereum Mainnet, securing 90% of the ETH-based assets before the malicious bot could react.
The Cost of Security: Bounties vs. Loss
Post-recovery, Foom.cash opted for full transparency. The protocol paid out $420,000 in recovery fees:
- $320,000 Bounty to @duha_real for the Base network rescue.
- $100,000 Fee to DecurityHQ for the Ethereum mainnet operation. Compared to a potential $2.26M total loss, the $1.84M recovery proves that active threat monitoring and having a relationship with the white-hat community is the best insurance for DeFi protocols.
Key Takeaways for Devs
- ZKP Security: Never assume a standard verifier library is "plug-and-play." Deployment parameters (like verifying the setup key) are critical.
- Active Defense: In DeFi, a "pause" function isn't always enough. You need white-hats who can front-run malicious actors in the mempool.
- Formal Verification: Always run formal verification on the circuit constraints to ensure no forged proofs can be validated.
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