MultiversX dApp Auditor

Audit the frontend components of MultiversX applications built with @multiversx/sdk-dapp. This skill focuses on client-side security, transaction construction, and wallet integration vulnerabilities.

When to Use

• Reviewing React/TypeScript dApp code
• Auditing wallet connection implementations
• Assessing transaction signing security
• Checking for XSS and data exposure vulnerabilities
• Validating frontend-backend security boundaries

1. Transaction Construction Security

The Threat Model

The frontend constructs transaction payloads that users sign. Vulnerabilities here can trick users into signing malicious transactions.

Payload Manipulation

// VULNERABLE: User input directly in transaction data
const sendTransaction = async (userInput: string) => {
    const tx = new Transaction({
        receiver: Address.newFromBech32(recipientAddress),
        data: Buffer.from(userInput),  // Attacker controls data!
        // ...
    });
    await signAndSend(tx);
};

// SECURE: Validate and sanitize all inputs
const sendTransaction = async (functionName: string, args: string[]) => {
    // Whitelist allowed functions
    const allowedFunctions = ['stake', 'unstake', 'claim'];
    if (!allowedFunctions.includes(functionName)) {
        throw new Error('Invalid function');
    }

    // Validate arguments
    const sanitizedArgs = args.map(arg => validateArgument(arg));

    const tx = new Transaction({
        receiver: contractAddress,
        data: Buffer.from(`${functionName}@${sanitizedArgs.join('@')}`),
        // ...
    });
    await signAndSend(tx);
};

Critical Checks

Check	Risk	Mitigation
Receiver address validation	Funds sent to wrong address	Validate against known addresses
Data payload construction	Malicious function calls	Whitelist allowed operations
Amount validation	Incorrect value transfers	Confirm amounts with user
Gas limit manipulation	Transaction failures	Use appropriate limits

2. Signing Security

Blind Signing Risks

Users may sign transactions without understanding the content:

// DANGEROUS: Signing opaque data
const signMessage = async (data: string) => {
    const hash = keccak256(data);
    return await wallet.signMessage(hash);  // User sees only hash!
};

// SECURE: Show clear message to user
const signMessage = async (message: string) => {
    // Display message to user before signing
    const confirmed = await showConfirmationDialog({
        title: 'Sign Message',
        content: `You are signing: "${message}"`,
        warning: 'Only sign messages you understand'
    });

    if (!confirmed) throw new Error('User rejected');
    return await wallet.signMessage(message);
};

Transaction Preview Requirements

Before signing, users should see:

• Recipient address (with verification if known)
• Amount being transferred
• Token type (EGLD, ESDT, NFT)
• Function being called (if smart contract interaction)
• Gas cost estimate

3. Sensitive Data Handling

Private Key Security

// CRITICAL VULNERABILITY: Never do this
localStorage.setItem('privateKey', wallet.privateKey);
localStorage.setItem('mnemonic', wallet.mnemonic);
sessionStorage.setItem('seed', wallet.seed);

// Check for these patterns in code review:
// - Any storage of private keys, mnemonics, or seeds
// - Logging of sensitive data
// - Sending sensitive data to APIs

Secure Patterns

// CORRECT: Use sdk-dapp's secure session management
import { initApp } from '@multiversx/sdk-dapp/out/methods/initApp/initApp';

initApp({
    storage: {
        getStorageCallback: () => sessionStorage  // Session only, not persistent
    },
    dAppConfig: {
        nativeAuth: {
            expirySeconds: 3600  // Short-lived tokens
        }
    }
});

Access Token Security

// VULNERABLE: Token exposed in URL
window.location.href = `https://api.example.com?accessToken=${token}`;

// VULNERABLE: Token in console
console.log('Auth token:', accessToken);

// SECURE: Token in Authorization header, never logged
fetch(apiUrl, {
    headers: {
        'Authorization': `Bearer ${accessToken}`
    }
});

4. XSS Prevention

User-Generated Content

// VULNERABLE: Direct HTML injection
const UserProfile = ({ bio }: { bio: string }) => {
    return <div dangerouslySetInnerHTML={{ __html: bio }} />;  // XSS!
};

// SECURE: React's default escaping
const UserProfile = ({ bio }: { bio: string }) => {
    return <div>{bio}</div>;  // Automatically escaped
};

// If HTML is necessary, sanitize first
import DOMPurify from 'dompurify';

const UserProfile = ({ bio }: { bio: string }) => {
    const sanitized = DOMPurify.sanitize(bio);
    return <div dangerouslySetInnerHTML={{ __html: sanitized }} />;
};

URL Handling

// VULNERABLE: Unvalidated redirect
const handleCallback = () => {
    const returnUrl = new URLSearchParams(window.location.search).get('returnUrl');
    window.location.href = returnUrl!;  // Open redirect!
};

// SECURE: Validate redirect URL
const handleCallback = () => {
    const returnUrl = new URLSearchParams(window.location.search).get('returnUrl');
    const allowed = ['/', '/dashboard', '/profile'];
    if (allowed.includes(returnUrl || '')) {
        window.location.href = returnUrl!;
    } else {
        window.location.href = '/';  // Default safe redirect
    }
};

5. API Communication Security

HTTPS Enforcement

// VULNERABLE: HTTP connection
const API_URL = 'http://api.example.com';  // Insecure!

// SECURE: Always HTTPS
const API_URL = 'https://api.example.com';

// Verify in code: all API URLs must use https://

Request/Response Validation

// VULNERABLE: Trusting API response blindly
const balance = await fetch('/api/balance').then(r => r.json());
displayBalance(balance.amount);  // What if API is compromised?

// SECURE: Validate response structure
const response = await fetch('/api/balance').then(r => r.json());
if (typeof response.amount !== 'string' || !/^\d+$/.test(response.amount)) {
    throw new Error('Invalid balance response');
}
displayBalance(response.amount);

6. Audit Tools and Techniques

Network Traffic Analysis

# Use browser DevTools Network tab to inspect:
# - All API requests and responses
# - Transaction data being sent
# - Headers (especially Authorization)
# - WebSocket messages

# Or use proxy tools:
# - Burp Suite
# - mitmproxy
# - Charles Proxy

Code Review Patterns

# Search for dangerous patterns
grep -r "localStorage" src/
grep -r "dangerouslySetInnerHTML" src/
grep -r "eval(" src/
grep -r "privateKey\|mnemonic\|seed" src/
grep -r "console.log" src/  # Check for sensitive data logging

Browser Security Headers Check

Content-Security-Policy: default-src 'self'; script-src 'self'
X-Frame-Options: DENY
X-Content-Type-Options: nosniff
Referrer-Policy: strict-origin-when-cross-origin

7. Authentication Flow Audit

Wallet Connection

// Verify wallet connection flow:
// 1. User initiates connection
// 2. Wallet provider prompts for approval
// 3. Only public address shared with dApp
// 4. No private data transmitted

// Check UnlockPanelManager usage
const unlockPanelManager = UnlockPanelManager.init({
    loginHandler: () => {
        // Verify: no sensitive data handling here
        navigate('/dashboard');
    }
});

Session Management

// Verify session security:
// - Token expiration enforced
// - Logout clears all session data
// - No persistent sensitive storage

const handleLogout = async () => {
    const provider = getAccountProvider();
    await provider.logout();
    // Verify: session storage cleared
    sessionStorage.clear();
    navigate('/');
};

8. Audit Checklist

Transaction Security

• All transaction data validated before signing
• User shown clear transaction preview
• Recipient addresses validated
• Amount confirmations for large transfers
• Gas limits appropriate for operation

Data Security

• No private keys in any storage
• No sensitive data in console logs
• Access tokens not exposed in URLs
• HTTPS enforced for all API calls

XSS Prevention

• No dangerouslySetInnerHTML with user input
• No eval() with user input
• URL redirects validated
• Content-Security-Policy headers present

Session Security

• Token expiration enforced
• Logout clears all session data
• Protected routes properly guarded
• Re-authentication for sensitive operations

9. Report Template

# dApp Security Audit Report

## Scope
- Application: [name]
- Version: [version]
- Files reviewed: [count]

## Findings

### Critical
| ID | Description | Location | Recommendation |
|----|-------------|----------|----------------|
| C1 | ... | ... | ... |

### High
...

### Medium
...

### Informational
...

## Recommendations Summary
1. [Priority recommendation]
2. ...

## Conclusion
[Overall assessment]