Solv Protocol Hack: $2.5M Double Mint Exploit

The Solv Protocol exploit resulted in approximately $2.5M in losses after an attacker exploited a logic flaw in the BitcoinReserveOffering contract. The vulnerability allowed the attacker to mint BRO tokens twice during a single mint flow, leading to massive token inflation. The issue stemmed from an interaction between the NFT transfer process and the onERC721Received callback. By triggering token minting inside the callback and then receiving another mint when execution returned to the main mint() function, the attacker was able to create unbacked BRO tokens. How the Exploit Happened? The attacker began with 135 BRO tokens, which were burned through the reserve contract. In return, the protocol issued a small amount of GOEFS tokens based on the current exchange rate. Using these tokens, the attacker initiated a mint transaction, sending GOEFS tokens along with a specific NFT. When the NFT was transferred, the contract triggered the onERC721Received callback, which internally executed