On February 21, 2025, the crypto world witnessed the largest single-event heist in history: $1.5 billion (401,347 ETH) was drained from Bybit's cold wallet in a matter of minutes.

The most terrifying part? The smart contracts worked perfectly. The Gnosis Safe multi-sig wallet, widely considered the gold standard of on-chain security, didn't have a single bug. Cryptography didn't fail. Instead, the hackers—officially attributed to the notorious state-sponsored Lazarus Group—exploited a massive blind spot that exists in almost every dApp today: the web interface supply chain.

As security researchers and developers, we need to treat this as a watershed moment. Here is exactly how they did it, why traditional smart contract audits miss this, and how we can prevent it from ever happening again.

🗺️ The Setup: Targeting the Weakest Link (The Web UI)

Multi-signature wallets require multiple authorized key holders (signers) to approve any outgoing transaction.…