Blockchain Ctf

Blockchain CTF

Solve blockchain and Web3 lab tasks by treating source, bytecode, storage, transactions, and contract state as one evidence graph, then proving the shortest exploit sequence on a local fork or authorized testnet.

When this skill applies

• Solidity, Vyper, EVM bytecode, ABI, deployed address lists, RPC URLs, transaction hashes, UTXO transaction IDs, event logs, contract frontends, or wallet-signature flows.
• Blockchain-forensics tasks involving peel chains, mixer-like fan-out/fan-in, transaction graph reconstruction, explorer APIs, account/UTXO flow tracing, internal transactions, or address clustering clues.
• Smart-contract patterns: proxy, factory, upgradeable implementation, delegatecall, low-level call, reentrancy, selfdestruct, storage collision, signature replay, oracle manipulation, governance, betting/market state, token accounting, calldata tricks, or ZK verifier logic.
• Tool cues: Foundry, Hardhat, cast, forge, anvil, solc, Slither, Mythril, Echidna, ethers.js, web3.py, blockchain explorer, or local fork.

Operating model

1. Collect chain context: network, chain ID when applicable, explorer/API path, accounts, transaction IDs, target addresses, ABI/source/bytecode if present, frontend bundle, factory/instance mapping, and success oracle.
2. Reconstruct contract graph: factory, proxy, implementation, libraries, token contracts, oracle contracts, verifier contracts, and privileged roles.
3. Inspect storage and calldata: EIP-1967 slots, packed variables, mappings, array slots, ABI coder assumptions, function selectors, and custom encodings.
4. For transaction-forensics tasks, reconstruct value flow before exploit logic: inputs, outputs, internal transfers, timing, amount correlation, change outputs, and likely peel-chain hops.
5. Run static and symbolic checks only after compiler version and source/bytecode match are known.
6. Build a local proof first when possible: anvil fork, Foundry test, Hardhat script, deterministic web3.py/ethers.js sequence, or read-only explorer trace.
7. Execute the minimal authorized transaction sequence and validate by event logs, storage diff, balance changes, returned flag, transaction graph endpoint, or isSolved-style oracle.

Technique integration

Load these when the adjacent domain appears:

• web-exploit-technique for Web3 frontends, auth nonces, wallet login flows, APIs, SSRF, or browser-admin interactions.
• vuln-exploit-technique for exploit-chain discipline and primitive-to-impact reasoning.
• fuzzing-technique for Echidna, Foundry fuzz, invariant testing, and state-machine exploration.
• crypto-technique for signatures, ECDSA nonce issues, ZK proof mistakes, commitments, and randomness.
• reversing-technique for bytecode-only targets, decompilation, metadata stripping, and function selector recovery.
• python-patterns for web3.py scripts and reproducible transaction orchestration.

Tool routing

• Foundry: foundry-cast for cast call, cast send, cast storage, cast calldata, cast sig, plus forge test, forge create, and anvil forks.
• Solidity toolchain: solc, compiler metadata, Yul IR output, storage layout, and ABI generation.
• Static and symbolic analysis: slither for detectors and summaries, mythril for path-sensitive issues, solc SMTChecker when source is available.
• Fuzzing: Foundry fuzz/invariants and Echidna for stateful bugs, accounting violations, and unexpected reachability.
• Automation: ethers.js, web3.py, Brownie-style scripts, RPC JSON calls, explorer APIs, and transaction receipt parsing.
• Bytecode and storage: decompilers, selector databases, raw eth_getStorageAt, traces, debug RPC, and event topic decoding.
• Transaction forensics: mempool.space-compatible APIs, Blockchair-style multi-chain explorers, Etherscan-compatible account/internal transaction APIs, CSV/JSON graphing, and Python networkx/pandas when a graph must be reconstructed.

Vulnerability checklist

• Access control: owner/admin/initializer/setter exposure, unprotected upgrade, tx.origin, role confusion.
• Reentrancy and callbacks: external calls before effects, token hooks, receive/fallback recursion, cross-function reentry.
• Proxy/delegatecall: EIP-1967 slots, storage layout mismatch, controlled implementation, controlled delegatecall target.
• Accounting: rounding, precision, rebasing, share/asset mismatch, unchecked return values, forced ETH, selfdestruct transfers.
• Oracle and market logic: stale price, spot-price manipulation, phantom IDs, unresolved state, missing existence checks.
• Signature and auth: replay, missing chain ID/domain separator, malleability, dirty address, unchecked signer, nonce reuse.
• Calldata and ABI: overlapping dynamic offsets, short calldata, custom fallback dispatch, ABI coder v1/v2 differences.
• Vault/token standards: ERC-4626 first-depositor share inflation via direct asset.transfer before initial deposit, rounding-direction abuse, decimals-offset defense skipped; ERC-777/hook-token reentry through tokensReceived.
• Account abstraction and delegation: ERC-4337 validateUserOp/validatePaymasterUserOp trust boundary, paymaster refund griefing, bundler-simulation vs on-chain-state gap, EntryPoint version mismatch; EIP-7702 (Pectra) 0xef0100 || address designators, init-frontrun on the authorization signature, delegation persists until re-signed.
• Compiler/bytecode: metadata stripping, optimizer/via-IR bugs, version-specific behavior; EIP-1153 transient storage (tstore/tload) is per-transaction — fine as a reentrancy lock, unsafe as cross-tx or cross-fork state.
• ZK/governance: trusted setup equality mistakes, public input mismatch, replayed proofs, missing nullifier tracking.

Safety and scope gates

• Treat mainnet-like or third-party contracts as read-only unless the user explicitly provides authorized lab/testnet scope.
• Never send value-bearing transactions without confirming target, chain ID, sender, value, and expected state diff.
• Prefer local fork reproduction before any broadcast.
• Stop after the success oracle is proven; do not drain extra funds or continue state manipulation.
• Record exact transaction sequence, calldata, storage observations, and validation output.

Resources

• references/web3-workflow.md — detailed smart-contract triage, storage, tooling, exploit, and validation workflow.
• references/transaction-forensics.md — read-only Bitcoin/UTXO and account-chain transaction tracing workflow.
• references/proxies-storage-and-upgrades.md — load when a proxy, delegatecall, initializer, or upgrade path controls the real state.
• references/foundry-forks-traces-and-proofs.md — load when proving a smart-contract bug locally with forks, traces, cheatcodes, and minimal transaction sequences.