Blockchain Security

• Deploy exploit contract that mirrors A's storage layout
• Exploit contract writes to A's storage slots via delegatecall
• Critical: Storage layout must match exactly (same slot ordering)
• See reference/delegatecall-attacks.md

2. CREATE Address Prediction (Nonce Manipulation)

Contract addresses from CREATE are deterministic: keccak256(rlp([sender, nonce]))[12:]

• Brute-force nonce to find which nonce produces target address
• Send dummy transactions (self-transfers) to increment nonce
• Deploy exploit contract at the exact nonce that hits target address
• See reference/create-address-prediction.md

3. Storage Layout & Slot Computation

• Mappings: keccak256(h(key) || uint256(slot_number))
  • Value types: h(k) = abi.encode(k) (left-padded to 32 bytes)
  • String/bytes: h(k) = keccak256(k)
• Read private variables via eth_getStorageAt
• See reference/storage-layout.md

4. Empty Array / Zero-Length Input Bypass

When a function loops over a user-supplied array to validate items (signatures, approvals, votes), passing an empty array skips the loop entirely. If there's no minimum-length check, validation is bypassed.

• Check: for (uint i = 0; i < arr.length; i++) with no require(arr.length >= N)
• Exploit: Call the function with [] to skip all validation

5. ECDSA Signature Malleability

Raw ecrecover accepts both (v, r, s) and (v', r, N-s) (where N = secp256k1 order, v flipped 27↔28). If a contract deduplicates signatures by hash of raw bytes, the malleable form has a different hash but recovers to the same signer.

• Check: ecrecover used without s <= N/2 enforcement (OpenZeppelin's ECDSA.sol enforces this)
• Exploit: Take a known valid signature, compute new_s = N - s, flip v, submit as "new" signature

6. Common Vulnerability Classes

Tools

# web3.py essentials
from web3 import Web3
w3 = Web3(Web3.HTTPProvider(RPC_URL))
acct = w3.eth.account.from_key(PRIVATE_KEY)

# Read private storage
w3.eth.get_storage_at(contract_addr, slot)

# Deploy contract
from solcx import compile_source, install_solc
install_solc("0.8.13")
compiled = compile_source(source, output_values=["abi", "bin"], solc_version="0.8.13")

# Send raw bytecode deployment
tx = {'data': bytecode, 'gas': 3000000, 'gasPrice': w3.eth.gas_price, 'nonce': nonce, 'chainId': chain_id}
signed = acct.sign_transaction(tx)
w3.eth.send_raw_transaction(signed.raw_transaction)

Reference

• Delegatecall Attacks
• CREATE Address Prediction
• Storage Layout

Critical Rules

• Always read storage before attacking (private vars are readable on-chain)
• Mirror exact storage layout when exploiting delegatecall
• For CREATE nonce brute-force, check nonces 0-100000+ systematically
• HTB instances are ephemeral -- script the full attack for speed