Oracle
The bridge feeding real-world data (prices, events) into smart contracts — and a single point of failure when it breaks.
Blockchains can’t natively see the outside world; oracles import external facts — asset prices above all — into smart contracts. Decentralized oracle networks like Chainlink aggregate many sources and nodes to make the feed manipulation-resistant. Everything in DeFi that references a price (lending, liquidations, derivatives) leans on one.
That reliance makes oracles a top attack surface: manipulate the feed (often via thin-liquidity markets it reads), and a protocol will mis-price collateral voluntarily — the mechanism behind numerous nine-figure exploits. When assessing a DeFi protocol, “which oracle, reading which markets, with what safeguards” is a first-order security question, not a technical footnote.