By focusing on the known weak spots you can significantly reduce the risk...

Smart Contracts Common Attacks
"No chain is stronger than its weakest link" — Arthur Conan Doyle, 1859-1930.

In the security context, this quote serves as a timeless reminder: your system is only as
secure as its weakest point. And hackers are always on the lookout for weaknesses.
But before we can defend something, we first need to understand how it can be
attacked. In this article, we’ll explore common attack vectors and offer guidance on how
to identify and mitigate them.

Understanding the Weak Spots

One major issue is that developers often make assumptions about how users will
interact with the system. Unfortunately, hackers live in the world of “what ifs,” finding
every possible way to break those assumptions. Poorly validated input or unexpected
actions are some of their favorite things to exploit.
Here are some of some examples of the common vulnerabilities and what you can do
about them.

1. User-Controlled Parameters in Storage
If users control inputs that affect where and how data is stored, you’re in dangerous
territory. An attacker could manipulate these inputs to overwrite key data like token
balances or ownership details. Imagine someone finding a way to give themselves extra
tokens—bad news.
How to fix it: Validate inputs rigorously. Set clear boundaries and ensure that user
inputs can’t mess with critical storage slots.

2. Gas-Related Issues
Unbounded loops or gas-inefficient code can make your contract vulnerable to denial-
of-service (DoS) attacks. When gas usage spirals out of control, your contract might just
fail. Smart Contract operations are expensive and blockchains have a limit of how much
gas can be spent in a block.

For example:
for (i = 0; i < accounts.length; i++) {
// Unbounded loop without limits
}

How to fix it: Always limit the number of iterations, optimize gas usage, and use safe
looping techniques to ensure your contract doesn’t choke under load.
3. Off-Chain Signatures and Replay Attacks
Off-chain signatures allow for cool features like gasless transactions, but they also open
the door to replay attacks. A valid signature can be reused maliciously unless you're
careful.
How to fix it: Use a nonce system to ensure each signature is only valid once. Track
used signatures and invalidate them after they’re processed.

4. VRF (Verifiable Random Function) and On-Chain Randomness
When your smart contract relies on randomness (like for lottery systems), if you use
easily manipulated inputs—like block timestamps or hashes—you’re inviting attackers to
control the outcome.
How to fix it: Combine multiple sources of randomness and avoid using easily
predictable values like block data.

5. Financial Attacks
DeFi contracts are especially vulnerable to financial tricks. Some common tactics:
● Oracle manipulation: If an attacker controls or manipulates the price feed, they
can exploit it for financial gain.
● Rounding errors: Handling large financial amounts without proper precision can
lead to exploitation.

● Unexpected balances: Without proper handling, attackers could exploit
unexpected changes in contract balances.
How to fix it: Use trusted oracles, apply strict rounding logic, and include functions that
handle balance sweeps to prevent manipulation.

6. Access Control Vulnerabilities
A common security flaw in smart contracts is improper access control mechanisms.
Functions like isAdmin() and their use should always be properly checked to avoid
exploitation by unauthorized parties.

Special Focus: DeFi Application Vulnerabilities
Each type of DeFi protocol comes with its own risks. Let’s highlight some key ones:
1. DEXs, AMMs, and Swaps
Common vulnerabilities include:
● Price manipulation: Through flash loans or oracle attacks, bad actors can
manipulate prices.
● Liquidity pool exploits: Imbalanced pools can be targeted.
● Rewards calculation flaws: Poorly calculated rewards can lead to overpayment.
2. Lending, Staking, and Insurance Protocols
Here’s what to watch out for:
● Oracle price manipulation: As these systems rely on price oracles, an attack here
could cause massive financial losses.
● Bad debt problems: Poorly managed loans or staking mechanisms could lead to
protocol insolvency.
3. Yield Farming
Yield farming protocols are prime targets for reward manipulation. Attackers often trick
the system to claim rewards they haven’t earned.
4. Algorithmic Stablecoins

Algorithmic stablecoins face unique challenges, especially around economic stability.
"Death spirals" (like the collapse of Terra/Luna) can devastate the system when price
mechanisms fail.

Final Thoughts
By focusing on the known weak spots discussed above, you can significantly reduce the
risk of exploitation and build trust within your DeFi ecosystem.