Rent Exempt Initialization Remediation

Overview

Detector Reference: Rent Exempt Initialization

This guide explains how to ensure accounts are funded with rent-exempt lamports before any data is written to them.

Recommended Fix

Use SystemProgram::create_account which atomically allocates, funds, and assigns ownership:

invoke(
    &system_instruction::create_account(
        payer.key,
        account.key,
        rent.minimum_balance(space),
        space as u64,
        program_id,
    ),
    &[payer.clone(), account.clone()],
)?;

// Now safe to write
let mut data = account.data.borrow_mut();
data[0..8].copy_from_slice(MY_DISCRIMINATOR);

Alternative Mitigations

1. Anchor init: #[account(init, payer = user, space = ...)] handles atomic creation.
2. Manual ordering: if not using create_account, always transfer lamports before writing data.
3. Pre-fund accounts: have users fund accounts in a prior transaction before initialization.

Common Mistakes

• Writing discriminator before funding: even a single byte write is risky if the account has zero lamports.
• Using CPI before funding: CPI calls that write to the account must also occur after funding.
• Assuming transaction atomicity protects against rent: while transactions are atomic, the runtime may validate rent at various points during execution.

References

• CWE-665: Improper Initialization
• Solana Rent