The $10 million Ronin bridge exploit on August 6 was caused by a faulty upgrade deployment script, according to blockchain security firm Verichains.
Cause of the Vulnerability
The upgrade reduced the voting threshold for validators to zero, allowing any user to withdraw from the bridge without a signature. Verichains states that the error occurred due to the incorrect initialization of the totalWeight variable.
How the Attack Happened
The attacker attempted to exploit this flaw but was front-run by an MEV bot, which actually carried out the attack, probably unintentionally. The bot’s owner later returned most of the funds to the Ronin team.
Consequences and Resolution
Verichains’ analysis reveals the risks of interacting with upgradeable smart contracts. The network could have lost the full amount had the attacker paid more in gas and thus avoided the front-run.
Due to the faulty upgrade script, Ronin bridge users were able to withdraw funds without validator signatures. This incident highlights the potential risks when dealing with upgradeable smart contracts.
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