Cross-chain bridges.

Today, Gravity Bridge was drained of roughly $5.4 million. The contracts held. Analysts believe the bridge's signing key was compromised, which let the attacker submit withdrawals that looked fully authorized.

Gravity Bridge connects Ethereum and Cosmos. It locks tokens on one chain and mints matching tokens on the other, and a set of validator signatures decides which transfers are valid. That signing set is the entire security model. Whoever holds the keys can move the locked pool.

This is why bridges keep showing up in incident reports. They concentrate custody of assets from multiple chains in one place, then guard all of it with a small group of signers. PeckShield counted at least eight major bridge exploits by mid-May, around $328 million.

A bridge is only as strong as the keys that authorize its withdrawals. Everything it holds sits behind that one assumption.