withdraw_vulnerable.rs

use anchor_lang::prelude::*;
use crate::state::Vault;

/// Withdraw lamports from vault - VULNERABLE version
///
/// ⚠️ VULNERABLE: This instruction allows withdrawing lamports without
/// checking if the remaining balance stays above rent-exempt minimum.
///
/// If the vault's lamports fall below rent-exemption threshold:
/// 1. The account becomes eligible for garbage collection
/// 2. The runtime may purge the account after the transaction
/// 3. All account data (including ownership info) is LOST
/// 4. The remaining lamports are LOST
#[derive(Accounts)]
pub struct WithdrawVulnerable<'info> {
    #[account(
        mut,
        seeds = [b"vault", owner.key().as_ref()],
        bump = vault.bump,
        has_one = owner
    )]
    pub vault: Account<'info, Vault>,

    #[account(mut)]
    pub owner: Signer<'info>,
}

pub fn handler(ctx: Context<WithdrawVulnerable>, amount: u64) -> Result<()> {
    let vault = &ctx.accounts.vault;
    let vault_info = vault.to_account_info();

    // Get current balance
    let vault_balance = vault_info.lamports();

    // ⚠️ VULNERABLE: Only checks if we have enough lamports
    // Does NOT check if remaining balance stays rent-exempt!
    require!(
        vault_balance >= amount,
        crate::error::ErrorCode::InsufficientFunds
    );

    // Transfer lamports out
    **vault_info.try_borrow_mut_lamports()? -= amount;
    **ctx.accounts.owner.try_borrow_mut_lamports()? += amount;

    let remaining = vault_info.lamports();
    msg!(
        "VULNERABLE: Withdrew {} lamports. Remaining: {} (may be below rent-exempt!)",
        amount,
        remaining
    );

    // ⚠️ If remaining < rent_exempt_minimum, this account could be purged!
    // The data and any remaining lamports would be LOST

    Ok(())
}