Smart Contract Audit — Learn Security by Practice

Master security through 60+ real-world audit challenges. Find bugs before attackers do.

Smart contract bugs have cost $3+ billion in losses since 2020. Reentrancy, access control flaws, and arithmetic errors are the top culprits. Auditing isn't optional — it's survival.

Top 5 Vulnerabilities to Master

Reentrancy

External calls before state updates allow attackers to drain funds recursively.

Integer Overflow/Underflow

Unchecked arithmetic can wrap around, minting infinite tokens or bypassing limits.

Access Control Flaws

Missing or incorrect modifiers let anyone call admin-only functions.

Unchecked External Calls

Ignoring return values from call, delegatecall, or transfer silently fails.

Front-Running

Attackers observe pending transactions and insert their own to steal value.

Example: Reentrancy Vulnerability

❌ Vulnerable

function withdraw() public {
    uint256 bal = balances[msg.sender];

    // External call BEFORE state update
    (bool ok, ) = msg.sender.call{value: bal}("");
    require(ok);

    balances[msg.sender] = 0; // Too late!
}

✅ Fixed

function withdraw() public {
    uint256 bal = balances[msg.sender];

    // State update BEFORE external call
    balances[msg.sender] = 0;

    (bool ok, ) = msg.sender.call{value: bal}("");
    require(ok);
}

The fix: Update state before making external calls (Checks-Effects-Interactions pattern). This prevents re-entering the function with stale state.

Practice on Solingo: 60 Audit Challenges

Each challenge contains real vulnerable code. Your job: find the bug, exploit it, then fix it. Hints and solutions included.

  • 20 beginner challenges (reentrancy, overflow, access control)
  • 25 intermediate (flash loan attacks, oracle manipulation)
  • 15 expert (MEV, governance exploits, complex DeFi)

Frequently Asked Questions

What is a smart contract audit?

A smart contract audit is a systematic review of code to identify security vulnerabilities, logic errors, and gas inefficiencies before deployment. It prevents exploits that could drain millions.

What are the most common vulnerabilities?

The top 5 are: reentrancy attacks, integer overflow/underflow, access control flaws, unchecked external calls, and front-running vulnerabilities.

How does Solingo teach auditing?

Through 60 hands-on challenges where you find and fix real vulnerabilities. Each challenge includes vulnerable code, hints, and step-by-step solutions.

Start Auditing Smart Contracts Today

Learn to find vulnerabilities before attackers do. 60 challenges, from beginner to expert.

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