Zploit 0-Day Shell

:: Editing File: invoice_save.php

<?php
    include 'check_login.php';
	include 'config/db.php';

if ($_SERVER['REQUEST_METHOD'] == 'POST') {

// Sanitize and collect invoice header data
    $client_id       = intval($_POST['client_id']);
    $invoice_no      = mysqli_real_escape_string($conn, $_POST['invoice_no']);
    $invoice_date    = mysqli_real_escape_string($conn, $_POST['invoice_date']);
    $payment_mode    = mysqli_real_escape_string($conn, $_POST['payment_mode']);
    $receiver_gstin  = mysqli_real_escape_string($conn, $_POST['receiver_gstin']);
    $receiver_address = mysqli_real_escape_string($conn, $_POST['receiver_address']);
    $sub_total       = floatval($_POST['sub_total']);
    $tax_total       = floatval($_POST['tax_total']);
    $grand_total     = floatval($_POST['grand_total']);

// Insert main invoice record
    $insert_invoice = "
        INSERT INTO invoices 
        (client_id, invoice_no, invoice_date, payment_mode, receiver_gstin, receiver_address, sub_total, tax_total, grand_total, created_at)
        VALUES 
        ('$client_id', '$invoice_no', '$invoice_date', '$payment_mode', '$receiver_gstin', '$receiver_address', '$sub_total', '$tax_total', '$grand_total', NOW())
    ";

if (mysqli_query($conn, $insert_invoice)) {
        $invoice_id = mysqli_insert_id($conn); // get inserted invoice ID

// Handle invoice items
        if (!empty($_POST['description']) && is_array($_POST['description'])) {
            $descriptions = $_POST['description'];
            $hsn_codes    = $_POST['hsn_code'];
            $prices       = $_POST['price'];
            $quantities   = $_POST['quantity'];
            $taxes        = $_POST['tax_percent'];
            $totals       = $_POST['taxable_amount'];

for ($i = 0; $i < count($descriptions); $i++) {
                $desc = mysqli_real_escape_string($conn, $descriptions[$i]);
                $hsn  = mysqli_real_escape_string($conn, $hsn_codes[$i]);
                $price = floatval($prices[$i]);
                $qty = floatval($quantities[$i]);
                $tax = floatval($taxes[$i]);
                $taxable = floatval($totals[$i]);

// Insert each item into invoice_items table
                $insert_item = "
                    INSERT INTO invoice_items 
                    (invoice_id, description, hsn_code, price, quantity, tax_percent, taxable_amount)
                    VALUES 
                    ('$invoice_id', '$desc', '$hsn', '$price', '$qty', '$tax', '$taxable')
                ";
                mysqli_query($conn, $insert_item);
            }
        }

// Redirect after success
        header("Location: invoice.php?success=1");
        exit();

} else {
        // Error handling
        echo "<div style='color:red; padding:20px;'>Error saving invoice: " . mysqli_error($conn) . "</div>";
    }
} else {
    echo "<div style='color:red; padding:20px;'>Invalid Request</div>";
}
?>