HACK ANALYSIS 3 min read

Unibot Hack Analysis

Overview:

On 31st Oct, 2023 Unibot was hacked due to a call injection attack, leading to a total loss of 500k$.

Smart Contract Hack Overview:

Attacker address: 0x413e4F
Vulnerable Contract:0x2b326a

Decoding the Smart Contract Vulnerability:

The root cause is a Call Injection. This vulnerability enabled attackers to inject their own malicious data into the 0xb2bd16ab() method, which subsequently allowed them to transfer tokens that were approved to Unibot contracts.

1. The attacker exploited the Unibot contract by obtaining excessively high token allowances for various addresses, surpassing their actual token balances.

2. The exploit contract systematically processes a list of addresses with elevated allowances (referred to as the ‘cd’ array).

– For each address, it examines the balance stored in ‘stor1’ within the Unibot contract.

– It also checks the allowance allocated within ‘stor1’ in the Unibot contract.

3. For each address in the list, it evaluates the Unibot balance through the ‘stor1.balanceOf()’ function and the allowance via ‘Unibot.allowance()’.

– When the allowance exceeds the balance, a callback to itself is initiated, passing along the address, the Unibot contract, balance, and allowance.

5. The self-triggered callback likely involves the execution of ‘transferFrom()’ with the excessively high allowance amount.

6. The crucial exploit lies in the self-callback:

– It relies on the inflated Unibot allowance to siphon off tokens.

– This circumvents the actual Unibot balances.

7. Consequently, the attacker successfully drains Unibot tokens from the contract into their own account, capitalizing on allowances surpassing the actual balances.

8. Replicating this process across multiple addresses with inflated allowances allows for the mass depletion of a significant total token amount.

Fig: The root cause of the vulnerability

Mitigation and Best Practices:

Users need to revoke approval for 0x126c9F.
Always validate your code by writing comprehensive test cases that cover all the possible business logic.
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Conclusion:

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Unibot Hack Analysis