What Is a Crypto Drainer?

A crypto drainer is a malicious smart contract designed to steal cryptocurrency, NFTs, and tokens from unsuspecting victims. Unlike traditional phishing that steals your seed phrase, drainers exploit a feature built into blockchain tokens: token approvals.

When you interact with decentralized applications (dApps), you often grant them permission to move tokens on your behalf. Drainers abuse this by tricking you into signing a transaction that grants unlimited approval to the attacker’s contract. Once signed, they can transfer everything you own—instantly and irreversibly.

How the Attack Works: Step by Step

Understanding the mechanics helps you recognize and avoid these scams:

1. The Lure: Fake Airdrops and NFT Mints

Scammers create professional-looking websites that promise free tokens, exclusive NFT mints, or ‘claim your rewards’ opportunities. These sites often:

• Impersonate legitimate projects (Uniswap, OpenSea, Blur, etc.)
• Use domains that look almost identical to real ones (e.g., unlswap.com instead of uniswap.org)
• Spread through compromised Twitter/X accounts, Discord servers, and Telegram groups
• Run Google Ads that appear above legitimate search results

2. The Connect: Wallet Integration

When you click ‘Connect Wallet,’ everything looks normal. Your MetaMask, Trust Wallet, or other Web3 wallet pops up. The site appears harmless at this stage—connecting your wallet alone doesn’t grant transaction permissions.

3. The Trap: Malicious Signature Request

After connecting, the site prompts you to ‘Claim’ your airdrop or ‘Mint’ your NFT. Your wallet displays a transaction for approval. This is where the attack happens.

The transaction may look innocent, showing vague text like:

• ‘SetApprovalForAll’
• ‘Approve’
• ‘Permit’
• A cryptic hex string

If you sign it, you’ve just granted the drainer contract permission to transfer all tokens of that type from your wallet—forever, until you manually revoke it.

4. The Drain: Instant Theft

Within seconds (often in the same block), the attacker’s bot detects your approval and executes transfers. Your NFTs, USDT, USDC, WETH, and any other approved tokens vanish. Because blockchain transactions are irreversible, recovery is nearly impossible.

Real-World Examples

Crypto drainers have caused hundreds of millions in losses:

• Inferno Drainer: Stole over million before ‘retiring’ in 2023—only to be succeeded by copycat operations
• Pink Drainer: Targeted NFT collectors with fake OpenSea and Blur links
• Angel Drainer: Used social engineering through compromised project Discord servers
• Monkey Drainer: Pioneered the drainer-as-a-service model, selling kits to other scammers

These aren’t isolated incidents. Drainer kits are sold on dark web forums, enabling anyone to launch attacks. The operators often take a 20-30%% cut of stolen funds.

Why Token Approvals Are Dangerous

Token approvals are a necessary part of how DeFi works. When you trade on Uniswap or list an NFT on OpenSea, you must approve the platform’s contract to handle your tokens. The problem is:

• Unlimited approvals: Many dApps request unlimited spending permissions for convenience, meaning the approval never expires
• Persistent permissions: Approvals remain active even after you disconnect your wallet or close the site
• Invisible risk: You can’t easily see your outstanding approvals without using specialized tools

How to Protect Yourself

Before Connecting

• Verify URLs meticulously: Type official URLs directly or use bookmarks. Never trust links from Twitter, Discord, or email
• Check the domain age: Scam sites are usually days or weeks old. Use WHOIS lookup tools
• Be skeptical of urgency: ‘Limited time,’ ‘ending soon,’ and ‘exclusive’ are manipulation tactics
• Research the project: Legitimate airdrops are announced on official channels, not random DMs

When Signing Transactions

• Read the transaction details: Look for ‘Approve,’ ‘SetApprovalForAll,’ or ‘Permit’ functions
• Understand what you’re approving: If a ‘free mint’ asks you to approve transferring your existing NFTs, that’s a red flag
• Use hardware wallets: They force you to physically confirm transactions, adding a moment for scrutiny
• Set spending limits: When possible, approve only the exact amount needed rather than unlimited

Regular Maintenance

• Audit your approvals: Use tools like Revoke.cash, Etherscan Token Approval Checker, or DeBank
• Revoke old approvals: Remove permissions from contracts you no longer use
• Use a burner wallet: Keep a separate wallet with minimal funds for trying new dApps

What to Do If You’ve Been Drained

If you suspect you’ve signed a malicious transaction:

1. Immediately transfer remaining assets to a fresh wallet (new seed phrase)
2. Revoke all approvals from the compromised wallet using Revoke.cash
3. Do NOT continue using the compromised wallet for anything valuable
4. Report the scam site to Chainabuse.com and browser safe-browsing lists
5. Document everything for potential law enforcement reports (transaction hashes, wallet addresses, screenshots)

The Bottom Line

Crypto drainers exploit trust and the technical complexity of blockchain transactions. They’re successful because the attack vector—token approvals—is a legitimate feature that most users don’t fully understand.

Your best defense is skepticism and vigilance. If someone offers you free money, ask yourself: Why? Legitimate projects don’t need to hunt for participants through DMs and fake links. And if you’re ever unsure about a transaction, the safest choice is simply not to sign.

Remember: On the blockchain, one wrong signature can empty your wallet in seconds. Take your time, verify everything, and treat every approval request as a potential threat until proven otherwise.