Module 02 — Reconnaissance & OSINT for Web3

Difficulty: Beginner → Intermediate

Reconnaissance is the first phase of any penetration test. In Web3, the transparent nature of public blockchains gives us extraordinary visibility — every transaction, every contract interaction, every token transfer is permanently recorded. This module teaches you how to systematically extract intelligence from on-chain and off-chain sources before touching a single line of Solidity.

2.1 On-Chain OSINT

Etherscan Deep Dive

Etherscan is far more than a block explorer. For a pentester, it’s the primary intelligence platform.

What to Extract from Etherscan:

Data Point Where to Find Security Relevance
Contract source code “Contract” tab → “Code” Review verified source; check compiler version, optimizer settings
Read/Write functions “Contract” tab → “Read/Write” Identify admin functions, state queries
Transaction history “Transactions” tab Deployment sequence, admin calls, suspicious patterns
Internal transactions “Internal Txns” tab DELEGATECALL, CREATE, ETH movements
Token transfers “Token Transfers” tab Token flow analysis, whale movements
Events/logs “Events” tab Ownership changes, parameter updates, pauses
Contract creator Top of contract page Trace back to deployer wallet, find related contracts
Similar contracts “Contract Diff” feature Compare against known-vulnerable versions 
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# Using Etherscan API for automated recon
export ETHERSCAN_API_KEY="YOUR_KEY"

# Get contract source code
curl "https://api.etherscan.io/api?module=contract&action=getsourcecode&address=0xCONTRACT&apikey=$ETHERSCAN_API_KEY"

# Get all transactions for an address
curl "https://api.etherscan.io/api?module=account&action=txlist&address=0xADDRESS&startblock=0&endblock=99999999&sort=asc&apikey=$ETHERSCAN_API_KEY"

# Get contract ABI
curl "https://api.etherscan.io/api?module=contract&action=getabi&address=0xCONTRACT&apikey=$ETHERSCAN_API_KEY"

Tenderly — Transaction Debugging

Tenderly provides step-by-step transaction execution traces, including state changes, gas usage per opcode, and call stack visualization.

Key features for recon:

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# Tenderly CLI — export project for simulation
tenderly export --project YOUR_PROJECT 0xTransactionHash

# Fork a network state at a specific block
tenderly fork --network mainnet --block-number 18500000

Dune Analytics — Custom On-Chain Queries

Dune lets you write SQL queries against decoded blockchain data. For auditors, this is invaluable for:

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-- Find all admin function calls on a contract
SELECT
    block_time,
    tx_hash,
    "from" AS caller,
    function_name
FROM ethereum.decoded_contracts
WHERE contract_address = 0xTARGET
  AND function_name IN ('setOwner', 'transferOwnership', 'pause', 'upgradeTo')
ORDER BY block_time DESC
LIMIT 100;

-- Track token distribution concentration
SELECT
    "to" AS holder,
    SUM(value) / 1e18 AS balance
FROM erc20_ethereum.evt_Transfer
WHERE contract_address = 0xTOKEN_ADDRESS
GROUP BY "to"
ORDER BY balance DESC
LIMIT 50;

Phalcon (BlockSec) — Attack Transaction Analysis

Phalcon specializes in dissecting exploit transactions. When analyzing a hack:

  1. Enter the transaction hash at phalcon.blocksec.com
  2. Phalcon shows the invocation flow — every call, with decoded function names, arguments, and return values
  3. Balance changes — which addresses gained/lost which tokens
  4. Fund flow — visual diagram of token movements

Practical Tip: When studying past exploits for CTF preparation or research, Phalcon is faster than reading Tenderly traces because it pre-labels known contracts and protocols.

2.2 Contract Verification Analysis

Verified vs. Unverified Contracts

Aspect Verified Unverified
Source code Available on Etherscan Only bytecode
Audit ability Full Solidity review Must decompile
Trust level Higher (but compiler bugs exist) Suspicious by default
Analysis tools Slither, Mythril, manual review Heimdall-rs, Dedaub, EtherVM

Analyzing Unverified Contracts

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# Step 1: Get the bytecode
cast code 0xUnverifiedContract --rpc-url $ETH_RPC

# Step 2: Try Dedaub online decompiler
# Upload bytecode at https://app.dedaub.com/decompile

# Step 3: Use heimdall-rs for advanced decompilation
heimdall decompile 0xUnverifiedContract --rpc-url $ETH_RPC --output ./decompiled/

# Step 4: Look for known selectors
heimdall decode 0xUnverifiedContract --rpc-url $ETH_RPC

# Step 5: Check Sourcify for partial verification
curl "https://sourcify.dev/server/check-all-by-addresses?addresses=0xCONTRACT&chainIds=1"

Compiler Version Analysis

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# Extract compiler version from metadata
cast code 0xContract | tail -c 86
# Last bytes contain CBOR-encoded metadata including Solidity version

# Check for known compiler bugs
# https://docs.soliditylang.org/en/latest/bugs.html
# Critical: Solidity 0.8.13-0.8.15 had optimizer bugs affecting ABI encoding

2.3 Proxy Pattern Detection

Identifying proxy patterns is critical — the code you see on Etherscan might not be the code actually executing.

Common Proxy Patterns

Pattern Detection Method Storage Slot
EIP-1967 Transparent Proxy Check slot 0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc Implementation address
EIP-1967 Admin Check slot 0xb53127684a568b3173ae13b9f8a6016e243e63b6e8ee1178d6a717850b5d6103 Admin address
EIP-1967 Beacon Check slot 0xa3f0ad74e5423aebfd80d3ef4346578335a9a72aeaee59ff6cb3582b35133d50 Beacon address
EIP-897 (DelegateProxy) Call implementation() Usually slot 0
Minimal Proxy (EIP-1167) Bytecode starts with 363d3d373d3d3d363d73 Hardcoded in bytecode
UUPS (EIP-1822) upgradeTo() in implementation, not proxy Same slot as EIP-1967
Diamond (EIP-2535) Multiple facets, diamondCut() function Mapping of selectors → facets 
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# Check for EIP-1967 implementation slot
cast storage 0xProxyAddress 0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc

# Check for EIP-1967 admin slot
cast storage 0xProxyAddress 0xb53127684a568b3173ae13b9f8a6016e243e63b6e8ee1178d6a717850b5d6103

# Detect minimal proxy pattern (EIP-1167)
cast code 0xAddress | grep -q "363d3d373d3d3d363d73" && echo "EIP-1167 Minimal Proxy detected"

# Get implementation from OpenZeppelin proxy
cast call 0xProxyAddress "implementation()(address)"

Proxy Detection Script

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// proxy-detect.js — Automated proxy pattern detection
const { ethers } = require("ethers");
const provider = new ethers.JsonRpcProvider(process.env.ETH_RPC);

async function detectProxy(address) {
    const results = {};

    // EIP-1967 implementation slot
    const implSlot = "0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc";
    const implData = await provider.getStorage(address, implSlot);
    if (implData !== ethers.ZeroHash) {
        results.type = "EIP-1967 Transparent/UUPS Proxy";
        results.implementation = ethers.getAddress("0x" + implData.slice(26));
    }

    // EIP-1967 beacon slot
    const beaconSlot = "0xa3f0ad74e5423aebfd80d3ef4346578335a9a72aeaee59ff6cb3582b35133d50";
    const beaconData = await provider.getStorage(address, beaconSlot);
    if (beaconData !== ethers.ZeroHash) {
        results.type = "Beacon Proxy";
        results.beacon = ethers.getAddress("0x" + beaconData.slice(26));
    }

    // EIP-1167 minimal proxy detection
    const code = await provider.getCode(address);
    if (code.startsWith("0x363d3d373d3d3d363d73")) {
        results.type = "EIP-1167 Minimal Proxy (Clone)";
        results.implementation = ethers.getAddress("0x" + code.slice(22, 62));
    }

    return results;
}

detectProxy("0xTargetAddress").then(console.log);

2.4 Admin & Owner Address Tracing

Identifying Privileged Roles

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# Common owner/admin function selectors
cast call 0xContract "owner()(address)"
cast call 0xContract "admin()(address)"
cast call 0xContract "governance()(address)"
cast call 0xContract "guardian()(address)"
cast call 0xContract "pendingOwner()(address)"

# For AccessControl (OpenZeppelin)
# DEFAULT_ADMIN_ROLE = 0x00
cast call 0xContract "getRoleMemberCount(bytes32)(uint256)" 0x0000000000000000000000000000000000000000000000000000000000000000
cast call 0xContract "getRoleMember(bytes32,uint256)(address)" 0x0000000000000000000000000000000000000000000000000000000000000000 0

# For Timelock controllers
cast call 0xContract "getMinDelay()(uint256)"

Multisig Identification

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# Gnosis Safe detection — check for known Safe functions
cast call 0xAddress "getThreshold()(uint256)" 2>/dev/null && echo "Gnosis Safe detected"

# Get Safe owners
cast call 0xSafe "getOwners()(address[])"

# Get threshold
cast call 0xSafe "getThreshold()(uint256)"

What to look for in admin analysis:

2.5 Deployer Wallet & Related Contract Analysis

Tracing Contract Relationships

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# Find who deployed a contract
cast receipt 0xDeploymentTxHash --field from

# Find all contracts deployed by an address
# Use Etherscan API:
curl "https://api.etherscan.io/api?module=account&action=txlist&address=0xDeployer&startblock=0&endblock=99999999&sort=asc&apikey=$ETHERSCAN_API_KEY" \
  | jq '.result[] | select(.to == "") | {hash: .hash, contractAddress: .contractAddress}'

Patterns to Look For

Pattern What It Indicates
Same deployer, multiple contracts Protocol ecosystem mapping
Deployer funds from Tornado Cash / Railgun Privacy-seeking deployer (could be legitimate or malicious)
CREATE2 deployments Deterministic addresses, possible metamorphic risk
Factory pattern deployments Protocol uses factory for pool/vault creation
Deployer renounces then reclaims via backdoor Potential rug pull setup

2.6 Protocol Dependency Mapping

What to Map

Every DeFi protocol depends on external systems. Map these dependencies to understand the full attack surface.

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┌─────────────────────────────────────────────────────┐
│                 Target Protocol                     │
├─────────────────────────────────────────────────────┤
│                                                     │
│  ┌──────────┐  ┌──────────┐  ┌───────────────────┐ │
│  │  Oracle   │  │   DEX    │  │   Lending Pool    │ │
│  │ Chainlink │  │ Uniswap  │  │   Aave / Comp     │ │
│  │ Band      │  │ Curve    │  │                   │ │
│  │ TWAP      │  │ Balancer │  │                   │ │
│  └──────────┘  └──────────┘  └───────────────────┘ │
│                                                     │
│  ┌──────────┐  ┌──────────┐  ┌───────────────────┐ │
│  │  Bridge   │  │  Token   │  │   Governance      │ │
│  │ LayerZero │  │  ERC20s  │  │   Timelock        │ │
│  │ Wormhole  │  │  wETH    │  │   Governor        │ │
│  │           │  │  stETH   │  │                   │ │
│  └──────────┘  └──────────┘  └───────────────────┘ │
└─────────────────────────────────────────────────────┘

Dependency checklist:

2.7 GitHub & Codebase Recon

What to Extract from a Protocol’s GitHub

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# Clone the repository
git clone https://github.com/protocol/contracts

# Check for audit reports
find . -name "*.pdf" -o -name "*audit*" -o -name "*security*" | head -20

# Look for TODO/FIXME/HACK comments — often mark incomplete security measures
grep -rn "TODO\|FIXME\|HACK\|XXX\|BUG\|SECURITY\|VULNERABLE" contracts/ --include="*.sol"

# Review recent changes to critical files
git log --oneline -20 contracts/core/

# Check for changes since last audit
git log --since="2024-01-01" --oneline contracts/

# Diff between audited commit and current deployment
git diff AUDITED_COMMIT..HEAD -- contracts/

# Find large recent commits (potential feature additions not yet audited)
git log --since="2024-06-01" --stat --diff-filter=M -- "*.sol" | head -100

Audit History Analysis

Checkpoint What to Look For
Audit report findings Were all findings addressed? Check the fix commits
Time since audit Code deployed long after audit may have unaudited changes
Scope coverage Was the full codebase audited, or only specific contracts?
Known limitations Auditors often list “out of scope” assumptions
Multiple audits Consensus across auditors increases confidence

2.8 Token Distribution & Whale Analysis

Why It Matters

Token distribution affects governance security, liquidity depth, and rug pull risk.

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# Using Etherscan Token Holder page
# https://etherscan.io/token/0xTOKEN#balances

# Top holder concentration
# If top 10 holders control >50% of supply → governance/dump risk

# Check if team tokens are locked
# Look for vesting contracts in top holders
cast call 0xVestingContract "beneficiary()(address)"
cast call 0xVestingContract "releaseTime()(uint256)"

Red Flags in Token Distribution

Signal Risk
Single address holds >20% Centralization / dump risk
Unlocked team tokens > circulating supply Potential rug pull
Large tokens in exchange hot wallets Imminent sell pressure
Recent large transfers to new wallets Possible pre-dump distribution
No liquidity locks LP can be pulled at any time

2.9 Social Engineering Vectors in Web3

Attack Surfaces Specific to Web3

Vector Description Example
Discord compromise Hijacked admin accounts post phishing links Bored Ape Yacht Club Discord hack
Fake governance proposals Malicious proposals disguised as benign Beanstalk governance attack
Compromised npm packages Malicious dependencies in project repos event-stream supply chain attack
Fake verified contracts Uploading misleading source code to Etherscan Honeypot tokens
Impersonation Fake team members in Telegram/Discord Social engineering validator keys
Phishing dApps Cloning legitimate frontends Fake Uniswap sites
DNS hijacking Redirecting protocol domains to malicious dApps Curve Finance DNS hijack

Recon on Social Channels

2.10 Subgraph Analysis (The Graph Protocol)

Querying Subgraphs for Recon

The Graph indexes blockchain data into queryable subgraphs. Many DeFi protocols expose their state via subgraphs.

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# Query a Uniswap V3 subgraph for large swaps (potential whale activity)
{
  swaps(
    first: 10,
    orderBy: amountUSD,
    orderDirection: desc,
    where: { pool: "0xPoolAddress" }
  ) {
    id
    timestamp
    amountUSD
    sender
    recipient
    amount0
    amount1
  }
}

# Query governance proposals
{
  proposals(
    first: 10,
    orderBy: startBlock,
    orderDirection: desc
  ) {
    id
    proposer
    description
    forVotes
    againstVotes
    status
  }
}

Subgraph recon targets:

2.11 Transaction History Pattern Analysis

What to Look For

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# Using cast to analyze recent transactions
cast etherscan-source 0xContract --chain mainnet
cast logs --from-block 18500000 --to-block latest --address 0xContract

Suspicious Patterns

Pattern Possible Implication
Many small test transactions before large ones Attacker rehearsing exploit
approve(MAX_UINT256) to unknown contracts Phishing approval or exploit setup
Flash loan interactions from new address Potential attack preparation
Rapid sequence of governance-related txs Governance attack in progress
Contract creation followed by immediate self-destruct Metamorphic contract attack
Multiple token approvals to same new contract Drainer contract setup

2.12 Tools Reference

Tool Purpose URL
Etherscan Block explorer, contract verification etherscan.io
Tenderly Tx debugging, simulation, forking tenderly.co
Phalcon Attack transaction analysis phalcon.blocksec.com
Dune Analytics Custom on-chain SQL queries dune.com
4byte.directory Function selector lookup 4byte.directory
Dedaub Bytecode decompilation app.dedaub.com
Sourcify Contract verification (alternative to Etherscan) sourcify.dev
Arkham Intelligence Wallet labeling, entity tracking arkhamintelligence.com
Nansen Wallet labeling, smart money tracking nansen.ai
Heimdall-rs Bytecode analysis CLI github.com/Jon-Becker/heimdall-rs
BlockSec Security monitoring, attack detection blocksec.com
cast (Foundry) CLI blockchain interaction Ships with Foundry

Recon Methodology Checklist

Use this checklist at the start of every engagement:

Key Takeaway: In Web3 pentesting, recon is disproportionately valuable compared to traditional web pentesting. Because blockchains are public, you can often identify vulnerabilities entirely through on-chain analysis before reading a single line of source code. Develop the habit of doing thorough recon — it saves hours of manual code review and often reveals attack vectors that pure code auditing misses.

*← Previous: Blockchain Fundamentals Next: Smart Contract Vulnerabilities →*