diff --git a/agent/invoice.php b/agent/invoice.php
index 3719004d..ade68ebd 100644
--- a/agent/invoice.php
+++ b/agent/invoice.php
@@ -226,12 +226,12 @@ if (isset($_GET['invoice_id'])) {
                                 </button>
                                 <div class="dropdown-menu">
                                     <?php if (!empty($config_smtp_host) && !empty($contact_email)) { ?>
-                                        <a class="dropdown-item" href="post.php?email_invoice=<?php echo $invoice_id; ?>">
+                                        <a class="dropdown-item" href="post.php?email_invoice=<?= $invoice_id ?>&csrf_token=<?= $_SESSION['csrf_token'] ?>">
                                             <i class="fas fa-fw fa-paper-plane mr-2"></i>Send Email
                                         </a>
                                         <div class="dropdown-divider"></div>
                                     <?php } ?>
-                                    <a class="dropdown-item" href="post.php?mark_invoice_sent=<?php echo $invoice_id; ?>">
+                                    <a class="dropdown-item" href="post.php?mark_invoice_sent=<?= $invoice_id ?>&csrf_token=<?= $_SESSION['csrf_token'] ?>">
                                         <i class="fas fa-fw fa-check mr-2"></i>Mark Sent
                                     </a>
                                 </div>
@@ -254,7 +254,7 @@ if (isset($_GET['invoice_id'])) {
                             <?php } ?>
 
                             <?php if (($invoice_status == 'Sent' || $invoice_status == 'Viewed') && $invoice_amount == 0 && $invoice_status !== 'Non-Billable') { ?>
-                                <a class="btn btn-dark" href="post.php?mark_invoice_non-billable=<?php echo $invoice_id; ?>">
+                                <a class="btn btn-dark" href="post.php?mark_invoice_non-billable=<?= $invoice_id ?>&csrf_token=<?= $_SESSION['csrf_token'] ?>">
                                     Mark Non-Billable
                                 </a>
                             <?php } ?>
@@ -285,14 +285,14 @@ if (isset($_GET['invoice_id'])) {
                                 <a class="dropdown-item" href="#" onclick="window.print();">
                                     <i class="fa fa-fw fa-print text-secondary mr-2"></i>Print
                                 </a>
-                                <a class="dropdown-item" href="post.php?export_invoice_pdf=<?php echo $invoice_id; ?>" target="_blank">
+                                <a class="dropdown-item" href="post.php?export_invoice_pdf=<?= $invoice_id ?>&csrf_token=<?= $_SESSION['csrf_token'] ?>" target="_blank">
                                     <i class="fa fa-fw fa-download text-secondary mr-2"></i>Download PDF
                                 </a>
-                                <a class="dropdown-item" href="post.php?export_invoice_packing_slip=<?php echo $invoice_id; ?>" target="_blank">
+                                <a class="dropdown-item" href="post.php?export_invoice_packing_slip=<?= $invoice_id ?>&csrf_token=<?= $_SESSION['csrf_token'] ?>" target="_blank">
                                     <i class="fa fa-fw fa-box-open text-secondary mr-2"></i>Packing Slip
                                 </a>
                                 <?php if (!empty($config_smtp_host) && !empty($contact_email)) { ?>
-                                    <a class="dropdown-item" href="post.php?email_invoice=<?php echo $invoice_id; ?>">
+                                    <a class="dropdown-item" href="post.php?email_invoice=<?= $invoice_id ?>&csrf_token=<?= $_SESSION['csrf_token'] ?>">
                                         <i class="fa fa-fw fa-paper-plane text-secondary mr-2"></i>Send Email
                                     </a>
                                 <?php } ?>
@@ -301,12 +301,12 @@ if (isset($_GET['invoice_id'])) {
                                 </a>
                                 <?php if ($invoice_status !== 'Cancelled' && $invoice_status !== 'Paid' && $invoice_status !== 'Non-Billable') { ?>
                                     <div class="dropdown-divider"></div>
-                                    <a class="dropdown-item text-danger text-bold confirm-link" href="post.php?cancel_invoice=<?php echo $invoice_id; ?>">
+                                    <a class="dropdown-item text-danger text-bold confirm-link" href="post.php?cancel_invoice=<?= $invoice_id ?>&csrf_token=<?= $_SESSION['csrf_token'] ?>">
                                         <i class="fa fa-fw fa-times mr-2"></i>Cancel
                                     </a>
                                 <?php } ?>
                                 <div class="dropdown-divider"></div>
-                                <a class="dropdown-item text-danger text-bold confirm-link" href="post.php?delete_invoice=<?php echo $invoice_id; ?>">
+                                <a class="dropdown-item text-danger text-bold confirm-link" href="post.php?delete_invoice=<?= $invoice_id ?>&csrf_token=<?= $_SESSION['csrf_token'] ?>">
                                     <i class="fas fa-fw fa-trash mr-2"></i>Delete
                                 </a>
                             </div>
@@ -430,7 +430,7 @@ if (isset($_GET['invoice_id'])) {
                                                                 <i class="fa fa-fw fa-edit mr-2"></i>Edit
                                                             </a>
                                                             <div class="dropdown-divider"></div>
-                                                            <a class="dropdown-item text-danger confirm-link" href="post.php?delete_invoice_item=<?php echo $item_id; ?>"><i class="fa fa-fw fa-trash mr-2"></i>Delete</a>
+                                                            <a class="dropdown-item text-danger confirm-link" href="post.php?delete_invoice_item=<?= $item_id ?>&csrf_token=<?= $_SESSION['csrf_token'] ?>"><i class="fa fa-fw fa-trash mr-2"></i>Delete</a>
                                                         </div>
                                                     </div>
                                                 </div>
@@ -449,6 +449,7 @@ if (isset($_GET['invoice_id'])) {
                                 ?>
                                 <tr class="d-print-none" <?php if ($invoice_status == "Paid" || $invoice_status == "Cancelled" || lookupUserPermission("module_sales") <= 1) { echo "hidden"; } ?>>
                                     <form action="post.php" method="post" autocomplete="off">
+                                        <input type="hidden" name="csrf_token" value="<?= $_SESSION['csrf_token'] ?>">
                                         <input type="hidden" name="invoice_id" value="<?= $invoice_id ?>">
                                         <input type="hidden" id="product_id" name="product_id" value="<?= $item_product_id ?? 0 ?>">
                                         <input type="hidden" name="item_order" value="<?php echo mysqli_num_rows($sql_invoice_items) + 1; ?>">
@@ -656,7 +657,7 @@ if (isset($_GET['invoice_id'])) {
                                     <td class="text-right"><?php echo numfmt_format_currency($currency_format, $payment_amount, $payment_currency_code); ?></td>
                                     <td><?php echo $payment_reference; ?></td>
                                     <td><?php echo $account_name; ?></td>
-                                    <td class="text-center"><a class="btn btn-light text-danger confirm-link" href="post.php?delete_payment=<?php echo $payment_id; ?>"><i class="fa fa-times"></i></a></td>
+                                    <td class="text-center"><a class="btn btn-light text-danger confirm-link" href="post.php?delete_payment=<?= $payment_id ?>&csrf_token=<?= $_SESSION['csrf_token'] ?>"><i class="fa fa-times"></i></a></td>
                                 </tr>
                                 <?php
                             }
diff --git a/agent/invoices.php b/agent/invoices.php
index a7c9ebb3..188869f5 100644
--- a/agent/invoices.php
+++ b/agent/invoices.php
@@ -421,18 +421,18 @@ $num_rows = mysqli_fetch_row(mysqli_query($mysqli, "SELECT FOUND_ROWS()"));
                                         </a>
                                         <div class="dropdown-divider"></div>
                                         <?php if (!empty($config_smtp_host)) { ?>
-                                            <a class="dropdown-item" href="post.php?email_invoice=<?php echo $invoice_id; ?>">
+                                            <a class="dropdown-item" href="post.php?email_invoice=<?= $invoice_id ?>&csrf_token=<?= $_SESSION['csrf_token'] ?>">
                                                 <i class="fas fa-fw fa-paper-plane mr-2"></i>Send Email
                                             </a>
                                             <div class="dropdown-divider"></div>
                                         <?php } ?>
                                         <?php if ($invoice_status == 'Draft') { ?>
-                                        <a class="dropdown-item" href="post.php?mark_invoice_sent=<?php echo $invoice_id; ?>">
+                                        <a class="dropdown-item" href="post.php?mark_invoice_sent=<?= $invoice_id ?>&csrf_token=<?= $_SESSION['csrf_token'] ?>">
                                             <i class="fas fa-fw fa-check mr-2"></i>Mark Sent
                                         </a>
                                         <div class="dropdown-divider"></div>
                                         <?php } ?>
-                                        <a class="dropdown-item text-danger text-bold confirm-link" href="post.php?delete_invoice=<?php echo $invoice_id; ?>">
+                                        <a class="dropdown-item text-danger text-bold confirm-link" href="post.php?delete_invoice=<?= $invoice_id ?>&csrf_token=<?= $_SESSION['csrf_token'] ?>">
                                             <i class="fas fa-fw fa-trash mr-2"></i>Delete
                                         </a>
                                     </div>
diff --git a/agent/modals/invoice/invoice_add.php b/agent/modals/invoice/invoice_add.php
index d952b033..47165002 100644
--- a/agent/modals/invoice/invoice_add.php
+++ b/agent/modals/invoice/invoice_add.php
@@ -14,6 +14,7 @@ ob_start();
     </button>
 </div>
 <form action="post.php" method="post" autocomplete="off">
+    <input type="hidden" name="csrf_token" value="<?= $_SESSION['csrf_token'] ?>">
 
     <div class="modal-body">
 
diff --git a/agent/modals/invoice/invoice_copy.php b/agent/modals/invoice/invoice_copy.php
index 0b286df3..d012ba91 100644
--- a/agent/modals/invoice/invoice_copy.php
+++ b/agent/modals/invoice/invoice_copy.php
@@ -22,6 +22,7 @@ ob_start();
     </button>
 </div>
 <form action="post.php" method="post" autocomplete="off">
+    <input type="hidden" name="csrf_token" value="<?= $_SESSION['csrf_token'] ?>">
     <input type="hidden" name="invoice_id" value="<?php echo $invoice_id; ?>">
 
     <div class="modal-body">
diff --git a/agent/modals/invoice/invoice_edit.php b/agent/modals/invoice/invoice_edit.php
index dc1a4494..ade2c39e 100644
--- a/agent/modals/invoice/invoice_edit.php
+++ b/agent/modals/invoice/invoice_edit.php
@@ -29,6 +29,7 @@ ob_start();
     </button>
 </div>
 <form action="post.php" method="post" autocomplete="off">
+    <input type="hidden" name="csrf_token" value="<?= $_SESSION['csrf_token'] ?>">
     <input type="hidden" name="invoice_id" value="<?php echo $invoice_id; ?>">
 
     <div class="modal-body" <?php if (lookupUserPermission('module_sales') <= 1) { echo 'inert'; } ?>>
diff --git a/agent/modals/invoice/invoice_export.php b/agent/modals/invoice/invoice_export.php
index d83999ab..c465a7ee 100644
--- a/agent/modals/invoice/invoice_export.php
+++ b/agent/modals/invoice/invoice_export.php
@@ -15,6 +15,7 @@ ob_start();
     </button>
 </div>
 <form action="post.php" method="post" autocomplete="off">
+    <input type="hidden" name="csrf_token" value="<?= $_SESSION['csrf_token'] ?>">
     <input type="hidden" name="client_id" value="<?= $client_id ?>">
     <div class="modal-body">
 
diff --git a/agent/modals/invoice/invoice_note.php b/agent/modals/invoice/invoice_note.php
index ed723fa2..daef7e90 100644
--- a/agent/modals/invoice/invoice_note.php
+++ b/agent/modals/invoice/invoice_note.php
@@ -8,8 +8,9 @@
         </button>
       </div>
       <form action="post.php" method="post" autocomplete="off">
+        <input type="hidden" name="csrf_token" value="<?= $_SESSION['csrf_token'] ?>">
         <input type="hidden" name="invoice_id" value="<?php echo $invoice_id; ?>">
-        <div class="modal-body">  
+        <div class="modal-body">
           <div class="form-group">
             <textarea class="form-control" rows="8" name="note" placeholder="Enter some notes"><?php echo $invoice_note; ?></textarea>
           </div>
@@ -21,4 +22,4 @@
       </form>
     </div>
   </div>
-</div>
\ No newline at end of file
+</div>
diff --git a/agent/modals/invoice/invoice_recurring_add.php b/agent/modals/invoice/invoice_recurring_add.php
index d2a07e5a..0c057867 100644
--- a/agent/modals/invoice/invoice_recurring_add.php
+++ b/agent/modals/invoice/invoice_recurring_add.php
@@ -20,6 +20,7 @@ ob_start();
     </button>
 </div>
 <form action="post.php" method="post" autocomplete="off">
+    <input type="hidden" name="csrf_token" value="<?= $_SESSION['csrf_token'] ?>">
     <input type="hidden" name="invoice_id" value="<?= $invoice_id ?>">
     <div class="modal-body">
         <div class="form-group">
diff --git a/agent/modals/invoice/item_edit.php b/agent/modals/invoice/item_edit.php
index 71e9a309..2395f53d 100644
--- a/agent/modals/invoice/item_edit.php
+++ b/agent/modals/invoice/item_edit.php
@@ -25,6 +25,7 @@ ob_start();
     </button>
 </div>
 <form action="post.php" method="post" autocomplete="off">
+    <input type="hidden" name="csrf_token" value="<?= $_SESSION['csrf_token'] ?>">
     <input type="hidden" name="item_id" value="<?php echo $item_id; ?>">
     <input type="hidden" name="product_id" value="<?php echo $product_id; ?>">
 
diff --git a/agent/post/invoice.php b/agent/post/invoice.php
index 53a322b1..870a7006 100644
--- a/agent/post/invoice.php
+++ b/agent/post/invoice.php
@@ -8,6 +8,10 @@ defined('FROM_POST_HANDLER') || die("Direct file access is not allowed");
 
 if (isset($_POST['add_invoice'])) {
 
+    validateCSRFToken($_POST['csrf_token']);
+
+    enforceUserPermission('module_sales', 2);
+
     require_once 'invoice_model.php';
 
     $client_id = intval($_POST['client']);
@@ -49,6 +53,10 @@ if (isset($_POST['add_invoice'])) {
 
 if (isset($_POST['edit_invoice'])) {
 
+    validateCSRFToken($_POST['csrf_token']);
+
+    enforceUserPermission('module_sales', 2);
+
     require_once 'invoice_model.php';
 
     $invoice_id = intval($_POST['invoice_id']);
@@ -83,6 +91,10 @@ if (isset($_POST['edit_invoice'])) {
 
 if (isset($_POST['add_invoice_copy'])) {
 
+    validateCSRFToken($_POST['csrf_token']);
+
+    enforceUserPermission('module_sales', 2);
+
     $invoice_id = intval($_POST['invoice_id']);
     $date = sanitizeInput($_POST['date']);
 
@@ -148,6 +160,10 @@ if (isset($_POST['add_invoice_copy'])) {
 
 if (isset($_GET['mark_invoice_sent'])) {
 
+    validateCSRFToken($_GET['csrf_token']);
+
+    enforceUserPermission('module_sales', 2);
+
     $invoice_id = intval($_GET['mark_invoice_sent']);
 
     // Get Invoice Number and Prefix and Client ID for Logging
@@ -171,6 +187,10 @@ if (isset($_GET['mark_invoice_sent'])) {
 
 if (isset($_GET['mark_invoice_non-billable'])) {
 
+    validateCSRFToken($_GET['csrf_token']);
+
+    enforceUserPermission('module_sales', 2);
+
     $invoice_id = intval($_GET['mark_invoice_non-billable']);
 
     // Get Invoice Number and Prefix and Client ID for Logging
@@ -194,6 +214,10 @@ if (isset($_GET['mark_invoice_non-billable'])) {
 
 if (isset($_GET['cancel_invoice'])) {
 
+    validateCSRFToken($_GET['csrf_token']);
+
+    enforceUserPermission('module_sales', 2);
+
     $invoice_id = intval($_GET['cancel_invoice']);
 
     // Get Invoice Number and Prefix and Client ID for Logging
@@ -217,6 +241,10 @@ if (isset($_GET['cancel_invoice'])) {
 
 if (isset($_GET['delete_invoice'])) {
 
+    validateCSRFToken($_GET['csrf_token']);
+
+    enforceUserPermission('module_sales', 3);
+
     $invoice_id = intval($_GET['delete_invoice']);
 
     // Get Invoice Number and Prefix and Client ID for Logging
@@ -262,6 +290,8 @@ if (isset($_GET['delete_invoice'])) {
 
 if (isset($_POST['add_invoice_item'])) {
 
+    validateCSRFToken($_POST['csrf_token']);
+
     enforceUserPermission('module_sales', 2);
 
     $invoice_id = intval($_POST['invoice_id']);
@@ -345,6 +375,8 @@ if (isset($_POST['add_invoice_item'])) {
 
 if (isset($_POST['invoice_note'])) {
 
+    validateCSRFToken($_POST['csrf_token']);
+
     enforceUserPermission('module_sales', 2);
 
     $invoice_id = intval($_POST['invoice_id']);
@@ -369,6 +401,8 @@ if (isset($_POST['invoice_note'])) {
 
 if (isset($_POST['edit_item'])) {
 
+    validateCSRFToken($_POST['csrf_token']);
+
     enforceUserPermission('module_sales', 2);
 
     $item_id = intval($_POST['item_id']);
@@ -469,6 +503,8 @@ if (isset($_POST['edit_item'])) {
 
 if (isset($_GET['delete_invoice_item'])) {
 
+    validateCSRFToken($_GET['csrf_token']);
+
     enforceUserPermission('module_sales', 2);
 
     $item_id = intval($_GET['delete_invoice_item']);
@@ -510,6 +546,10 @@ if (isset($_GET['delete_invoice_item'])) {
 
 if (isset($_GET['email_invoice'])) {
 
+    validateCSRFToken($_GET['csrf_token']);
+
+    enforceUserPermission('module_sales', 2);
+
     $invoice_id = intval($_GET['email_invoice']);
 
     $sql = mysqli_query($mysqli,"SELECT * FROM invoices
@@ -632,6 +672,8 @@ if (isset($_GET['email_invoice'])) {
 
 if (isset($_POST['export_invoices_csv'])) {
 
+    validateCSRFToken($_POST['csrf_token']);
+
     enforceUserPermission('module_sales');
 
     if ($_POST['client_id']) {
@@ -697,6 +739,10 @@ if (isset($_POST['export_invoices_csv'])) {
 
 if (isset($_POST['link_invoice_to_ticket'])) {
 
+    validateCSRFToken($_POST['csrf_token']);
+
+    enforceUserPermission('module_sales', 2);
+
     $invoice_id = intval($_POST['invoice_id']);
     $ticket_id = intval($_POST['ticket_id']);
 
@@ -710,6 +756,10 @@ if (isset($_POST['link_invoice_to_ticket'])) {
 
 if (isset($_POST['add_ticket_to_invoice'])) {
 
+    validateCSRFToken($_POST['csrf_token']);
+
+    enforceUserPermission('module_sales', 2);
+
     $invoice_id = intval($_POST['invoice_id']);
     $ticket_id = intval($_POST['ticket_id']);
 
@@ -723,6 +773,10 @@ if (isset($_POST['add_ticket_to_invoice'])) {
 
 if (isset($_GET['export_invoice_pdf'])) {
 
+    validateCSRFToken($_GET['csrf_token']);
+
+    enforceUserPermission('module_sales');
+
     $invoice_id = intval($_GET['export_invoice_pdf']);
 
     $sql = mysqli_query(
@@ -946,6 +1000,10 @@ if (isset($_GET['export_invoice_pdf'])) {
 
 if (isset($_GET['export_invoice_packing_slip'])) {
 
+    validateCSRFToken($_GET['csrf_token']);
+
+    enforceUserPermission('module_sales');
+
     $invoice_id = intval($_GET['export_invoice_packing_slip']);
 
     $sql = mysqli_query(
@@ -1087,6 +1145,10 @@ if (isset($_GET['export_invoice_packing_slip'])) {
 
 if (isset($_POST['bulk_edit_invoice_category'])) {
 
+    validateCSRFToken($_POST['csrf_token']);
+
+    enforceUserPermission('module_sales', 2);
+
     $category_id = intval($_POST['bulk_category_id']);
 
     // Get Category name for logging and Notification