The rise of blockchain-hosted malware like Omnistealer and the growing scale of approval phishing attacks — which identified over 20,000 victims in a single international law enforcement operation on April 11, 2026 — demand a more sophisticated approach to crypto security than occasional manual checks. This tutorial walks you through building an automated cross-chain approval monitoring system that alerts you to dangerous smart contract permissions across every network where you hold assets.
The Objective
By the end of this tutorial, you will have a system that scans your wallet addresses across Ethereum, Binance Smart Chain, Polygon, Arbitrum, and other EVM-compatible networks for active token approvals. It will flag unlimited approvals, identify risky or unknown spenders, and generate a consolidated report you can review weekly. This is not a beginner setup — it requires familiarity with command-line tools, basic scripting, and understanding of ERC-20 token mechanics.
The context motivating this build is clear. Bitcoin trades at approximately $73,054 and Ethereum at $2,285 as of April 2026, meaning a compromised wallet can result in catastrophic losses. The Omnistealer malware demonstrated that attackers now host malicious code permanently on blockchains like TRON and BSC, and approval phishing has become a multi-billion-dollar criminal industry. Manual revocation is no longer sufficient.
Prerequisites
Before starting, ensure you have the following. A Linux or macOS system with Python 3.10 or higher installed. Node.js 18 or higher for interacting with blockchain RPCs. Wallet addresses you want to monitor, available in plain text or from your wallet software. RPC endpoints for each network you use — free tiers from Ankr, Alchemy, or Infura are sufficient for personal use. A basic understanding of how ERC-20 approvals work, including the allowance() function that returns the remaining approved amount for any spender.
You will also need the following Python packages: web3 for blockchain interaction, requests for API calls, and pandas for data processing. Install them with pip install web3 requests pandas.
Step-by-Step Walkthrough
Step 1: Configure your network endpoints. Create a configuration file called networks.json that maps each blockchain to its RPC endpoint and block explorer API. For Ethereum mainnet, use your Alchemy or Infura URL. For BSC, use the public RPC at https://bsc-dataseed.binance.org or a premium endpoint for faster queries. For Polygon, Arbitrum, Optimism, and Avalanche, add corresponding RPC URLs. Include the chain ID and the ERC-20 proxy contract address for each network, as approval data is typically stored at the proxy level.
Step 2: Build the approval scanner. Write a Python script that iterates through each network configuration and queries the approval events for your wallet address. Use the Web3.py library to call the allowance() function on each ERC-20 token contract. The script should compare the returned allowance against the token’s total supply to identify unlimited approvals — those where the allowance equals or exceeds type(uint256).max (approximately 1.16 times 10 to the 77th power).
Step 3: Classify spenders by risk level. Not all approvals are equally dangerous. Build a classification system that categorizes spenders into three tiers. Known protocols with audited contracts like Uniswap, Aave, or Compound are low risk. Recently deployed contracts with no audit history and limited transaction counts are medium risk. Unknown addresses or contracts flagged by blockchain security services are high risk. You can cross-reference spender addresses against databases like CoinGecko’s contract registry or Etherscan’s verified contract list.
Step 4: Set up automated scheduling. Use cron on Linux or launchd on macOS to run your scanner daily. The script should output a JSON report with all active approvals, flagged by risk level. Configure it to send an alert — via email, Telegram bot, or a simple desktop notification — whenever a new high-risk approval is detected or when an existing approval’s risk level changes.
Step 5: Build the dashboard. For a visual overview, use a lightweight tool like Grafana or a simple HTML page that reads your JSON reports. The dashboard should display each network as a column, with token approvals listed by risk level. Include one-click revoke links that open your wallet interface directly to the revocation transaction for each flagged approval.
Troubleshooting
If your scanner returns zero approvals for an address where you know you have active permissions, the most common cause is using the wrong RPC endpoint or querying a token contract that uses a non-standard approval mechanism. Some tokens, notably USDT on Ethereum, require setting the allowance to zero before setting a new value, and the approval function may behave differently than standard ERC-20.
Rate limiting is another frequent issue when using free-tier RPC endpoints. If you encounter 429 errors, add a delay between requests or upgrade to a paid tier. For wallets with many interactions, the initial scan can take several minutes per network. Subsequent scans can be optimized by tracking only approval and revocation events since the last check using block number filters.
If the dashboard shows stale data, check that your cron job is running correctly and that the output file path matches what the dashboard is reading. Use absolute paths in your cron configuration to avoid environment-related issues.
Mastering the Skill
Once you have the basic system running, consider these advanced enhancements. Integrate on-chain reputation scoring from services like Forta or Halsen to automatically assess the risk of newly detected spender contracts. Add support for non-EVM chains like Solana and TRON, which use different approval mechanisms but are equally vulnerable to phishing. Implement a time-decay function that automatically revokes approvals that have not been used within a configurable period, such as 30 days. Finally, contribute your findings back to community databases to help other users identify known scam contracts.
The cryptocurrency security landscape in 2026 demands proactive defense. With approval phishing generating billions in losses and blockchain-hosted malware like Omnistealer making traditional takedowns impossible, the responsibility for protecting your assets falls squarely on you. Building this monitoring system takes a few hours but provides ongoing protection that manual checking cannot match.
Disclaimer: This article is for educational purposes only and does not constitute financial or security advice. Always test new tools with small amounts before relying on them for significant holdings.
20,000 victims from approval phishing in a single operation and people still blindly sign unlimited token allowances. education is the real bottleneck
education alone wont fix it. wallets need to default to exact-amount approvals and make unlimited a conscious opt-in. the UX is the vulnerability
Finally, a guide that goes beyond just ‘revoke your approvals.’ Building a custom dashboard for multi-chain visibility is exactly what the space needs right now. I’ve been stung by stale approvals on obscure L2s before, so the cross-chain logic here is a lifesaver for my security workflow.
I’m a bit skeptical about adding another layer of complexity to my setup. If I’m building a dashboard to audit my approvals, doesn’t that dashboard itself become a huge target for exploiters if not secured properly? I’d love to see more on how we can trust the data coming from multiple network RPCs without centralizing the risk.
Sarah Jenkins valid concern about the dashboard itself being a target. the guide recommends local execution with no cloud dependencies for exactly that reason
This is huge for anyone farming on 5+ chains. Tracking what you’ve signed on Base, Arbitrum, and Mainnet simultaneously is a nightmare without a unified view. Most people don’t realize how many infinite approvals they have sitting around from years ago lol. Definitely going to try implementing the multi-network listener this weekend.
infinite approvals on Base and Arbitrum from 2023 are a ticking time bomb. most people audit mainnet and forget the L2s entirely
The analysis of cross-chain approval patterns is spot on. We often see users forget about permissions on sidechains that they haven’t touched in months. Standardizing the auditing process across different VM implementations is the real challenge, but this approach seems robust. Great technical breakdown on the event filtering logic.