The first two weeks of September 2024 saw more than $28 million stolen from DeFi protocols through a combination of reentrancy attacks and flash loan exploits. For newcomers to decentralized finance, headlines about hacks and stolen funds can be intimidating — but they also offer valuable lessons. Understanding how these attacks work and learning to evaluate protocol safety before depositing your funds is one of the most important skills you can develop as a crypto user. This guide walks you through the essentials of DeFi safety in plain language, no technical background required.
The Basics
Decentralized finance, or DeFi, allows you to lend, borrow, trade, and earn interest on your crypto without going through a bank or centralized exchange. Instead, you interact with smart contracts — self-executing programs on the blockchain that automatically process transactions according to predetermined rules. While this eliminates the need for intermediaries, it also means there is no customer service hotline to call if something goes wrong. When a smart contract is exploited, funds are typically gone permanently.
The two most common types of DeFi attacks in September 2024 were reentrancy attacks and flash loan exploits. A reentrancy attack occurs when a hacker tricks a smart contract into executing the same operation multiple times before it has finished updating its records — imagine being able to withdraw money from an ATM multiple times before your balance is updated. A flash loan exploit uses a special type of crypto loan that must be repaid within a single transaction to manipulate token prices and drain liquidity pools.
Why It Matters
Unlike traditional banking, where deposits are insured by government programs like the FDIC, DeFi has no safety net. If a protocol is exploited and your funds are stolen, there is no guarantee you will recover them. The Penpie hack in September 2024 resulted in $27 million in losses, and by September 8, all stolen funds had been laundered through Tornado Cash, making recovery virtually impossible. Understanding risk is not about avoiding DeFi entirely — it is about making informed decisions about where and how much to invest.
Getting Started Guide
Step 1: Check for audits. Before depositing funds into any DeFi protocol, check whether it has been audited by reputable security firms. Look for audit reports from companies like Trail of Bits, OpenZeppelin, Certik, or ConsenSys Diligence. Audits are not guarantees of safety, but they significantly reduce the likelihood of common vulnerabilities. You can usually find audit reports linked from the protocol’s official website or documentation.
Step 2: Evaluate the team. Research who built the protocol. Are the developers publicly known with verifiable track records? Anonymous teams are not automatically untrustworthy — some of the most successful crypto projects were built by pseudonymous developers — but they do add an extra layer of risk. Look for active GitHub repositories, regular updates, and engaged community management.
Step 3: Assess the total value locked. Total Value Locked, or TVL, represents the total amount of crypto deposited in a protocol. While a high TVL is not a guarantee of safety, protocols with billions of dollars in TVL have generally been battle-tested by the market. Be cautious of new protocols offering extremely high returns with very low TVL — these are often targets for exploits or outright scams.
Step 4: Understand the smart contract risk. If a protocol interacts with other protocols — for example, a yield farming platform that deposits funds into multiple lending protocols — the attack surface increases with each additional integration. The Penpie exploit was partially enabled by its interaction with Pendle Finance markets. Ask yourself: how many external dependencies does this protocol have?
Step 5: Limit your exposure. Never invest more than you can afford to lose in any single protocol. A good rule of thumb is to limit your exposure to any one platform to no more than 5-10% of your total crypto portfolio. This way, even if the worst happens, your losses are manageable.
Common Pitfalls
New DeFi users frequently fall into several traps. Chasing extremely high annual percentage yields — anything above 50% should be treated with extreme skepticism. Approving unlimited token allowances without understanding what you are authorizing. Investing in protocols with no audit history simply because friends or social media influencers recommended them. Failing to revoke old token approvals that are no longer needed, leaving wallets exposed to potential exploits. And perhaps most importantly, not taking the time to understand what a protocol actually does before depositing funds.
Next Steps
DeFi can be a powerful tool for growing your crypto holdings, but only if you approach it with the same caution you would apply to any financial decision. Start small, learn the basics, and gradually increase your exposure as your understanding grows. Tools like DeFiLlama and Token Terminal can help you research protocols before investing. Browser extensions like Revoke.cash allow you to manage and revoke token approvals. The more you learn, the better equipped you will be to navigate the DeFi landscape safely and confidently.
Disclaimer: This article is for educational purposes only and does not constitute financial or investment advice. Always conduct your own research before engaging with any DeFi protocol.
no customer service hotline is the most important sentence in this whole guide. once the tx confirms, its gone. that mindset shift is everything for new people
moonboi no customer service hotline is the sentence that should be on every dex landing page in 48pt font. once the tx confirms its gone is the whole thesis
that sentence should be printed on every dex landing page. once confirmed its gone would save a lot of people from expensive lessons
good primer. the point about checking if a protocol has been audited AND when the audit was done matters. an audit from 2022 means nothing if the codebase has changed significantly since
ape_first_think_later_ right that phishing does more damage but $28M in two weeks from contract exploits means teams are still shipping broken code. both problems at once
the audit diff check is underrated advice. most people just look for the audit badge and assume its current. big mistake
this is the key point people miss. a protocol can be audited in january, deploy a new contract in march, and the audit covers nothing. always check the diff
reentrancy attacks in 2024 is embarrassing. OpenZeppelin has had ReentrancyGuard for years. if your contract doesnt use it youre negligent at this point
28M from reentrancy and flash loans in 2024 when OpenZeppelin ReentrancyGuard exists for free. teams shipping without it are negligent full stop
guard_skip_ ReentrancyGuard being one line of code is the painful part. teams skip it to save 5000 gas on deployment and lose 8 figures. priorities are completely backwards
reentrancy_ghost_ ReentrancyGuard is literally one line of code. teams shipping without it in 2024 should be publicly named
28M in two weeks from reentrancy and flash loans when ReentrancyGuard exists for free. teams shipping without it in 2024 is beyond negligent
reentrancy in 2024 after OpenZeppelin shipped ReentrancyGuard for free is just negligence. no excuse at all
the audit diff point cannot be overstated. protocols pass audit, deploy new code, and users assume the badge still applies. it doesnt
the audit diff point is critical. protocols pass audit in january, deploy unaudited changes in march, users think the badge still applies
reentrancy attacks in 2024 is wild. the pattern was documented in 2016 after the DAO hack and people still forget the checks-effects-interactions pattern
noir_dev_ checks-effects-interactions has been standard since 2016 but most exploits come from composability not single contract bugs. multiple protocols interacting creates attack paths audits miss
noir_dev_ checks-effects-interactions has been documented since 2016 but composability between protocols creates attack vectors no single audit catches. the DAO hack was one contract, modern exploits chain across 3-4 protocols
the audit diff point is so underrated. a protocol can pass audit in january deploy new code in march and the badge still says audited. always check what changed
fresh_rekt_ most beginners dont even know what etherscan is let alone how to diff contract deployments. the UX gap in DeFi safety is enormous
the flash loan explanation is solid but honestly most people getting rekt are clicking fake discord links not getting hit by complex exploits. phishers do more damage than hackers
ape_first_think_later_ right that phishing does more damage but try telling a beginner to diff contract deployments. the real safety upgrade is better wallet defaults not more homework
$28M in two weeks from reentrancy and flash loans. these are solved problems technically, the issue is teams not implementing the fixes
the flash loan exploit explanation is really well done for beginners. most guides skip the mechanics and just say dont ape into unaudited protocols
the audit badge problem is real. protocols pass audit in january, swap out a contract in march, and users think nothing changed