Security Best Practices for Solana Smart Contracts

With the rise of DeFi hacks and exploits, security should be the top priority for Solana developers. Implementing best practices from the start ensures your smart contracts are safe from vulnerabilities that could lead to significant financial losses.

Why Security Matters

The crypto space has seen billions lost to smart contract exploits:

🔹 2024: Over $2 billion lost to hacks across all chains
🔹 Common attacks: Reentrancy, arithmetic overflow, access control failures
🔹 Solana-specific: Account validation issues, PDA seed collisions

A single vulnerability can destroy user trust and project viability.

Key Security Best Practices

1. Follow the Principle of Least Privilege

Only grant accounts the permissions they absolutely need:

// Bad: Anyone can call this
pub fn dangerous_function(ctx: Context<Dangerous>) -> Result<()> {
    // No access control!
    do_sensitive_operation()?;
    Ok(())
}

// Good: Only authority can call
pub fn safe_function(ctx: Context<Safe>) -> Result<()> {
    require!(
        ctx.accounts.authority.key() == ctx.accounts.config.authority,
        ErrorCode::Unauthorized
    );
    do_sensitive_operation()?;
    Ok(())
}

2. Validate All Inputs

Never trust user input—validate everything:

pub fn transfer(ctx: Context<Transfer>, amount: u64) -> Result<()> {
    // Validate amount
    require!(amount > 0, ErrorCode::InvalidAmount);
    require!(amount <= MAX_TRANSFER, ErrorCode::ExceedsLimit);
    
    // Validate accounts
    require!(
        ctx.accounts.from.owner == ctx.accounts.user.key(),
        ErrorCode::InvalidOwner
    );
    
    // Process transfer
    Ok(())
}

3. Use Safe Math

Prevent integer overflows and underflows:

use anchor_lang::prelude::*;

// Anchor's checked math (recommended)
let result = amount_a.checked_add(amount_b)
    .ok_or(ErrorCode::MathOverflow)?;

// Or use require! for explicit checks
require!(
    amount_a <= u64::MAX - amount_b,
    ErrorCode::MathOverflow
);

4. Proper Account Validation

Always validate account ownership and type:

#[derive(Accounts)]
pub struct SecureInstruction<'info> {
    // Validate the account is owned by the expected program
    #[account(
        mut,
        constraint = token_account.owner == user.key() @ ErrorCode::InvalidOwner,
        constraint = token_account.mint == expected_mint.key() @ ErrorCode::InvalidMint
    )]
    pub token_account: Account<'info, TokenAccount>,
    
    // Validate signer
    pub user: Signer<'info>,
    
    // Validate PDA derivation
    #[account(
        seeds = [b"config", user.key().as_ref()],
        bump = config.bump
    )]
    pub config: Account<'info, Config>,
}

5. Avoid Common Vulnerabilities

Missing Signer Checks:

// Always verify signers
#[account(signer)]
pub authority: AccountInfo<'info>,

Account Confusion:

// Use discriminators and type checking
#[account]
pub struct MyAccount {
    pub discriminator: [u8; 8], // Anchor handles this automatically
    pub data: u64,
}

PDA Seed Collisions:

// Use unique, specific seeds
#[account(
    seeds = [
        b"user_data",
        user.key().as_ref(),
        pool.key().as_ref(), // Include multiple identifiers
    ],
    bump
)]
pub user_data: Account<'info, UserData>,

6. Conduct Thorough Testing

Write comprehensive tests covering edge cases:

describe("security tests", () => {
  it("rejects unauthorized access", async () => {
    const attacker = Keypair.generate();
    
    await expect(
      program.methods
        .adminFunction()
        .accounts({ authority: attacker.publicKey })
        .signers([attacker])
        .rpc()
    ).to.be.rejectedWith("Unauthorized");
  });

  it("handles maximum values", async () => {
    await program.methods
      .transfer(new BN(u64.MAX))
      .accounts({...})
      .rpc();
    // Verify no overflow
  });
});

7. Perform Security Audits

Before mainnet deployment:

🔹 Internal review: Multiple team members review code
🔹 External audit: Hire professional auditors
🔹 Bug bounty: Set up a program for ongoing security

Recommended auditors:

Solana-Specific Security Considerations

Account Ownership

Always verify account ownership:

require!(
    account.owner == &expected_program_id,
    ErrorCode::InvalidOwner
);

Rent Exemption

Ensure accounts have sufficient rent:

#[account(
    init,
    payer = payer,
    space = 8 + std::mem::size_of::<MyAccount>(),
    rent_exempt = enforce // Anchor enforces this
)]
pub my_account: Account<'info, MyAccount>,

CPI Security

When calling other programs:

// Validate the program being called
require!(
    ctx.accounts.token_program.key() == &spl_token::ID,
    ErrorCode::InvalidProgram
);

// Use invoke_signed carefully with PDAs

Security Checklist Before Deployment

All accounts properly validated
Signer checks in place
Math operations use checked arithmetic
Access control implemented
PDAs use unique, collision-resistant seeds
Comprehensive test coverage (>90%)
Internal code review completed
External audit performed
Bug bounty program established

Ongoing Security

After deployment:

🔹 Monitor for suspicious activity
🔹 Have an incident response plan
🔹 Consider upgrade mechanisms for critical fixes
🔹 Keep dependencies updated
🔹 Participate in security communities

Securing your smart contract from the start can save you from costly exploits. Security is not optional—it's essential for building trust in the Solana ecosystem!