"Web3" is the umbrella term for applications built on public blockchains — cryptocurrency wallets, tokens, NFTs, and the smart contracts that govern them. NovaCart bundles a whole family of Web3 challenges because this technology brings a security model that is unfamiliar to most web developers, and several assumptions that are safe for an ordinary web app are exactly wrong here.
This is a foundations lesson. Rather than drilling a single exploit, it builds the mental model you need so that NovaCart's Web3 challenges — and any smart-contract review you do later — make sense.
Lab availability note: NovaCart's Web3 features (wallet, sandbox, NFT pages) are gated behind a feature flag and depend on a wallet and a local test chain — they are version- and configuration-dependent and are often absent in the default Docker image. If they are not available in your instance, skip the observation step, complete the quizzes, and optionally follow the Remix + testnet alternative described in the Lab step. The conceptual understanding the lesson builds is fully accessible without a live lab.
A blockchain is an append-only ledger replicated across many independent nodes. Instead of one database controlled by one party, every participant holds a copy, and new entries (grouped into blocks) are agreed by a consensus mechanism. Three properties drive everything in this lesson:
- Immutability. Once a block is accepted and buried under later blocks, rewriting history is infeasible — and so is editing a contract's deployed code.
- Transparency. On a public chain, every transaction, every contract's bytecode, and every value it stores is readable by anyone. There is no confidentiality by default.
- Cost (gas). Every state-changing operation costs gas, paid in the chain's native currency. Gas meters computation and storage, and also shapes some attacks.
In this lesson you will:
- Learn what a blockchain, a wallet, and a smart contract are, and how a transaction is signed.
- See why on-chain data is public and why a deployed-contract bug cannot be patched in place.
- Name the classic smart-contract vulnerability classes — reentrancy, integer over/underflow (over-mint), missing access control, honeypots, and front-running — and map them to NovaCart's Web3 challenges.
Estimated time: 10 to 15 minutes.
When you are ready, send the Continue signal.