In February 2026, the decentralized lending protocol Moonwell became the first major security failure of the "vibe coding" era. The incident, which resulted in a net loss of $1.78 million, was not the work of a sophisticated hacker or a structural flaw in legacy code. Instead, it was a logic error in a smart contract co-authored by Anthropic's Claude Opus 4.6. [...] Rather than multiplying the cbETH/ETH exchange rate by the ETH/USD price feed, the AI-generated code used the raw exchange ratio as if it were already denominated in dollars. [...] [...]
One missing multiplication. The code went in through governance proposal MIP-X43 to integrate Chainlink's OEV wrappers, and a security researcher traced the pull requests to commits co-authored by Claude Opus 4.6. Within four minutes liquidation bots had seized 1,096 cbETH for pennies. It is the clearest financial number on this page attached to generated code, and the reason it is here rather than in a crypto column is the shape of the bug: not a vulnerability anybody could scan for, but a unit error that reads perfectly and is wrong. Moonwell had lost money to oracle problems twice before without any AI involved, which is the honest caveat: the assistant supplied the error, and the system that let one line of arithmetic reach production unchecked was already there.
Alessandro Pignati, NeuralTrust, in NeuralTrust