diff --git a/installwizard.php b/installwizard.php
index d9dfecc23..a05d6fb6e 100755
--- a/installwizard.php
+++ b/installwizard.php
@@ -2,28 +2,29 @@
     include_once('constants.php');
     include_once('config.php');
 
-    /* Version check before we include this. */
-    $phpVersion = phpversion();
-    $phpVersionParts = explode('.', $phpVersion);
-    if ($phpVersionParts[0] >= 5)
+    $minimumPHPVersion = '8.4.1';
+    $isSupportedPHPVersion = version_compare(
+        PHP_VERSION,
+        $minimumPHPVersion,
+        '>='
+    );
+
+    if ($isSupportedPHPVersion)
     {
         include_once(LEGACY_ROOT . '/lib/Template.php');
         include_once(LEGACY_ROOT . '/lib/Session.php');
         include_once(LEGACY_ROOT . '/lib/TemplateUtility.php');
 
-        @session_name(CATS_SESSION_NAME);
+        session_name(CATS_SESSION_NAME);
         session_start();
     }
-    else
-    {
-        $php4 = true;
-    }
+
 
     $installLibURL = 'js/lib.js';
     $installScriptURL = 'js/install.js';
     $subModalScriptURL = 'js/submodal/subModal.js';
     $installCSSURL = 'modules/install/install.css';
-    if (!isset($php4))
+    if ($isSupportedPHPVersion)
     {
         $installLibURL = call_user_func(array('TemplateUtility', 'getVersionedAssetURL'), $installLibURL);
         $installScriptURL = call_user_func(array('TemplateUtility', 'getVersionedAssetURL'), $installScriptURL);
@@ -37,7 +38,7 @@
     <head>
         <title>OpenCATS - Installation Wizard Script</title>
         <?php
-            if (!isset($php4) && isset($_SESSION['CATS']) && $_SESSION['CATS']->isLoggedIn())
+            if ($isSupportedPHPVersion && isset($_SESSION['CATS']) && $_SESSION['CATS']->isLoggedIn())
             {
                 echo '<script type="text/javascript">CATSCsrfToken = ',
                      Template::escapeJs($_SESSION['CATS']->getCSRFToken()), ';</script>', "\n";
@@ -122,7 +123,14 @@
                                             <br />
                                             <span style="font-weight: bold;">Test Results</span>
                                             <table class="test_output">
-                                            <tr class="fail"><td>PHP 5.0.0 or greater is required to run OpenCATS. Found version: <?php echo(phpversion()); ?>.</td></tr>
+                                            <tr class="fail">
+                                            <td>
+                                            OpenCATS requires PHP
+                                            <?php echo htmlspecialchars($minimumPHPVersion, ENT_QUOTES, 'UTF-8'); ?>
+                                            or newer. Found PHP
+                                            <?php echo htmlspecialchars(PHP_VERSION, ENT_QUOTES, 'UTF-8'); ?>.
+                                            </td>
+                                            </tr>
                                             </table>
                                         </div>
                                         <div id="databaseConnectivity" style="display: none;">
@@ -466,7 +474,7 @@
                                                     <td>Please choose your time zone.</td>
                                                 </tr>
                                                 <tr>
-                                                    <td style="padding-bottom: 10px;"><?php if (!isset($php4)) TemplateUtility::printTimeZoneSelect('timeZone', 'width: 420px;', '', OFFSET_GMT); ?></td>
+                                                    <td style="padding-bottom: 10px;"><?php if ($isSupportedPHPVersion) TemplateUtility::printTimeZoneSelect('timeZone', 'width: 420px;', '', OFFSET_GMT); ?></td>
                                                 </tr>
 
                                                 <tr>
@@ -567,7 +575,7 @@
                             </table>
 
                             <script type="text/javascript">
-                                <?php if (!isset($php4)): ?>
+                                <?php if ($isSupportedPHPVersion): ?>
                                     Installpage_populate('a=startInstall');
                                 <?php else: ?>
                                     setActiveStep(1);
diff --git a/lib/CATSUtility.php b/lib/CATSUtility.php
index 85fda1936..e9969ba79 100755
--- a/lib/CATSUtility.php
+++ b/lib/CATSUtility.php
@@ -168,14 +168,30 @@ public static function changeConfigSetting($name, $value)
         }
 
         $result = @file_put_contents(
-            'config.php', implode("\n", $newconfig) . "\n"
+            'config.php',
+            implode("\n", $newconfig) . "\n"
         );
+
         if (!$result)
         {
             /* We either completely failed or wrote 0 bytes. */
             return false;
         }
 
+        /*
+         * Ensure subsequent requests see the updated configuration immediately
+         * when PHP OPcache is enabled.
+         */
+        if (function_exists('opcache_invalidate'))
+        {
+            $configPath = realpath('config.php');
+
+            if ($configPath !== false)
+            {
+                opcache_invalidate($configPath, true);
+            }
+        }
+
         return true;
     }
 
diff --git a/lib/InstallationTests.php b/lib/InstallationTests.php
index c2f91bc66..dd2a083cd 100755
--- a/lib/InstallationTests.php
+++ b/lib/InstallationTests.php
@@ -367,126 +367,261 @@ public static function checkZipExtension()
     public static function checkMySQL($host, $user, $pass, $name)
     {
         /* Check MySQL connection. */
-		$db = @mysqli_connect($host, $user, $pass);
-        if (self::DEBUG_FAIL || !$db)
+        try
+        {
+            $db = mysqli_connect($host, $user, $pass);
+        }
+        catch (mysqli_sql_exception $exception)
         {
             echo sprintf(
                 '<tr class="fail"><td>Cannot connect to database.<pre class="fail">%s</pre></td></tr>',
-                mysqli_connect_error()
+                htmlspecialchars($exception->getMessage(), ENT_QUOTES, 'UTF-8')
             );
+
+            return false;
+        }
+
+        if (self::DEBUG_FAIL || $db === false)
+        {
+            echo sprintf(
+                '<tr class="fail"><td>Cannot connect to database.<pre class="fail">%s</pre></td></tr>',
+                htmlspecialchars(mysqli_connect_error(), ENT_QUOTES, 'UTF-8')
+            );
+
             return false;
         }
 
         echo '<tr class="pass"><td>MySQL connection was successful.</td></tr>';
 
         /* Check MySQL version number. */
-        if (!self::_checkMySQLVersion($db))
+        try
         {
+            $versionPassed = self::_checkMySQLVersion($db);
+        }
+        catch (mysqli_sql_exception $exception)
+        {
+            echo sprintf(
+                '<tr class="fail"><td>Cannot retrieve MySQL version number.<pre class="fail">%s</pre></td></tr>',
+                htmlspecialchars($exception->getMessage(), ENT_QUOTES, 'UTF-8')
+            );
+
+            mysqli_close($db);
+            return false;
+        }
+
+        if (!$versionPassed)
+        {
+            mysqli_close($db);
             return false;
         }
 
         /* Try to switch to the CATS database. */
-        if (!@mysqli_select_db($db, $name))
+        try
+        {
+            $databaseSelected = mysqli_select_db($db, $name);
+        }
+        catch (mysqli_sql_exception $exception)
         {
             echo sprintf(
                 '<tr class="fail"><td>Failed to select database \'%s\'.<pre class="fail">%s</pre></td></tr>',
-                $name,
-                mysqli_connect_error()
+                htmlspecialchars($name, ENT_QUOTES, 'UTF-8'),
+                         htmlspecialchars($exception->getMessage(), ENT_QUOTES, 'UTF-8')
             );
+
+            mysqli_close($db);
+            return false;
+        }
+
+        if (!$databaseSelected)
+        {
+            echo sprintf(
+                '<tr class="fail"><td>Failed to select database \'%s\'.<pre class="fail">%s</pre></td></tr>',
+                htmlspecialchars($name, ENT_QUOTES, 'UTF-8'),
+                         htmlspecialchars(mysqli_error($db), ENT_QUOTES, 'UTF-8')
+            );
+
+            mysqli_close($db);
             return false;
         }
 
         echo sprintf(
             '<tr class="pass"><td>Database \'%s\' selected.</td></tr>',
-            $name
+            htmlspecialchars($name, ENT_QUOTES, 'UTF-8')
         );
 
         /* Check CREATE TABLE permissions. */
-        $queryResult = @mysqli_query($db, 'CREATE TABLE `testtable` (`id` int(11) NOT NULL default \'0\') ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;');
+        try
+        {
+            $queryResult = mysqli_query(
+                $db,
+                'CREATE TABLE `testtable` (`id` int(11) NOT NULL default \'0\') '
+                . 'ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;'
+            );
+        }
+        catch (mysqli_sql_exception $exception)
+        {
+            $queryResult = false;
+        }
+
         if (!$queryResult)
         {
-            mysqli_query($db, 'DROP TABLE testtable');
-            $queryResult = @mysqli_query($db, 'CREATE TABLE `testtable` (`id` int(11) NOT NULL default \'0\') ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;');
+            try
+            {
+                mysqli_query($db, 'DROP TABLE testtable');
+            }
+            catch (mysqli_sql_exception $exception)
+            {
+                /* Ignore cleanup failure and retry CREATE below. */
+            }
+
+            try
+            {
+                $queryResult = mysqli_query(
+                    $db,
+                    'CREATE TABLE `testtable` (`id` int(11) NOT NULL default \'0\') '
+                    . 'ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;'
+                );
+            }
+            catch (mysqli_sql_exception $exception)
+            {
+                $queryResult = false;
+            }
         }
+
         if (!$queryResult)
         {
             echo sprintf(
                 '<tr class="fail"><td>Cannot create table \'testtable\'. Please verify that '
                 . '\'ALL PERMISSIONS\' were granted to the \'%s\' user for the \'%s\' database. '
                 . 'You may also have to recreate the database before trying again.',
-                $user,
-                $name
+                htmlspecialchars($user, ENT_QUOTES, 'UTF-8'),
+                         htmlspecialchars($name, ENT_QUOTES, 'UTF-8')
             );
+
+            mysqli_close($db);
             return false;
         }
 
-        echo sprintf(
-            '<tr class="pass"><td>Can create \'testtable\' table.</td></tr>'
-        );
+        echo '<tr class="pass"><td>Can create \'testtable\' table.</td></tr>';
 
         /* Check INSERT permissions. */
-        if (!@mysqli_query($db, 'INSERT INTO testtable (id) VALUES (1)'))
+        try
+        {
+            $queryResult = mysqli_query(
+                $db,
+                'INSERT INTO testtable (id) VALUES (1)'
+            );
+        }
+        catch (mysqli_sql_exception $exception)
+        {
+            $queryResult = false;
+        }
+
+        if (!$queryResult)
         {
             echo sprintf(
                 '<tr class="fail"><td>Cannot insert into \'testtable\' table. Please verify that '
                 . '\'ALL PERMISSIONS\' were granted to the \'%s\' user for the \'%s\' database. '
                 . 'You may also have to recreate the database before trying again.',
-                $user,
-                $name
+                htmlspecialchars($user, ENT_QUOTES, 'UTF-8'),
+                         htmlspecialchars($name, ENT_QUOTES, 'UTF-8')
             );
+
+            mysqli_close($db);
             return false;
         }
 
         echo '<tr class="pass"><td>Can insert into \'testtable\' table.</td></tr>';
 
         /* Check UPDATE permissions. */
-        if (!@mysqli_query($db, 'UPDATE testtable SET id = 5 WHERE id = 1'))
+        try
+        {
+            $queryResult = mysqli_query(
+                $db,
+                'UPDATE testtable SET id = 5 WHERE id = 1'
+            );
+        }
+        catch (mysqli_sql_exception $exception)
+        {
+            $queryResult = false;
+        }
+
+        if (!$queryResult)
         {
             echo sprintf(
                 '<tr class="fail"><td>Cannot update \'testtable\' table. Please verify that '
                 . '\'ALL PERMISSIONS\' were granted to the \'%s\' user for the \'%s\' database. '
                 . 'You will also need to re-import the database schema.',
-                $user,
-                $name
+                htmlspecialchars($user, ENT_QUOTES, 'UTF-8'),
+                         htmlspecialchars($name, ENT_QUOTES, 'UTF-8')
             );
+
+            mysqli_close($db);
             return false;
         }
 
         echo '<tr class="pass"><td>Can update \'testtable\' table.</td></tr>';
 
         /* Check DELETE permissions. */
-        if (!@mysqli_query($db, 'DELETE FROM testtable WHERE id = 5'))
+        try
+        {
+            $queryResult = mysqli_query(
+                $db,
+                'DELETE FROM testtable WHERE id = 5'
+            );
+        }
+        catch (mysqli_sql_exception $exception)
+        {
+            $queryResult = false;
+        }
+
+        if (!$queryResult)
         {
             echo sprintf(
                 '<tr class="fail"><td>Cannot delete from \'testtable\' table. Please verify that '
                 . '\'ALL PERMISSIONS\' were granted to the \'%s\' user for the \'%s\' database. '
                 . 'You will also need to re-import the database schema.',
-                $user,
-                $name
+                htmlspecialchars($user, ENT_QUOTES, 'UTF-8'),
+                         htmlspecialchars($name, ENT_QUOTES, 'UTF-8')
             );
+
+            mysqli_close($db);
             return false;
         }
 
         echo '<tr class="pass"><td>Can delete from \'testtable\' table.</td></tr>';
 
-        /* Check DROP TABLES permissions. */
-        if (!@mysqli_query($db, 'DROP TABLE testtable'))
+        /* Check DROP TABLE permissions. */
+        try
+        {
+            $queryResult = mysqli_query($db, 'DROP TABLE testtable');
+        }
+        catch (mysqli_sql_exception $exception)
+        {
+            $queryResult = false;
+        }
+
+        if (!$queryResult)
         {
             echo sprintf(
                 '<tr class="fail"><td>Cannot drop table \'testtable\'. Please verify that '
                 . '\'ALL PERMISSIONS\' were granted to the \'%s\' user for the \'%s\' database. '
                 . 'You will also need to re-import the database schema.',
-                $user,
-                $name
+                htmlspecialchars($user, ENT_QUOTES, 'UTF-8'),
+                         htmlspecialchars($name, ENT_QUOTES, 'UTF-8')
             );
+
+            mysqli_close($db);
             return false;
         }
 
         echo '<tr class="pass"><td>Can drop table \'testtable\'.</td></tr>';
 
+        mysqli_close($db);
         return true;
     }
 
+
     public static function checkAttachmentsDir()
     {
         return (!self::DEBUG_FAIL && self::_checkReadWrite('./attachments'));
diff --git a/modules/install/ajax/ui.php b/modules/install/ajax/ui.php
index f9c28a0d2..4604294e3 100755
--- a/modules/install/ajax/ui.php
+++ b/modules/install/ajax/ui.php
@@ -124,34 +124,41 @@
          */
         if (isset($_REQUEST['user']))
         {
-            if (isset($_REQUEST['user']) && !empty($_REQUEST['user']))
-            {
-                CATSUtility::changeConfigSetting('DATABASE_USER', var_export($_REQUEST['user'], true));
-            }
+            $databaseUser = trim($_REQUEST['user']);
+            $databaseHost = trim($_REQUEST['host'] ?? '');
+            $databaseName = trim($_REQUEST['name'] ?? '');
 
+            /* A blank password means keep the existing configured password. */
             if (isset($_REQUEST['pass']) && $_REQUEST['pass'] !== '')
             {
-                CATSUtility::changeConfigSetting('DATABASE_PASS', var_export($_REQUEST['pass'], true));
+                $databasePass = $_REQUEST['pass'];
             }
-
-            if (isset($_REQUEST['host']) && !empty($_REQUEST['host']))
+            else
             {
-                CATSUtility::changeConfigSetting('DATABASE_HOST', var_export($_REQUEST['host'], true));
+                $databasePass = DATABASE_PASS;
             }
 
-            if (isset($_REQUEST['name']) && !empty($_REQUEST['name']))
-            {
-                CATSUtility::changeConfigSetting('DATABASE_NAME', var_export($_REQUEST['name'], true));
-            }
+            $testRequest = http_build_query(
+                array(
+                    'a'    => 'testDatabaseConnectivity',
+                    'user' => $databaseUser,
+                    'pass' => $databasePass,
+                    'host' => $databaseHost,
+                    'name' => $databaseName
+                ),
+                '',
+                '&',
+                PHP_QUERY_RFC3986
+            );
 
             echo '
-                <script type="text/javascript">
-                    setActiveStep(2);
-                    showTextBlock(\'databaseConnectivity\');
-                    document.getElementById(\'testDatabaseConnectivity\').disabled = true;
-                    document.getElementById(\'testDatabaseConnectivityIndicator\').style.visibility = \'visible\';
-                    Installpage_append(\'a=testDatabaseConnectivity\', \'Please wait while your connection is tested...\');
-                </script>';
+            <script type="text/javascript">
+            setActiveStep(2);
+            showTextBlock(\'databaseConnectivity\');
+            document.getElementById(\'testDatabaseConnectivity\').disabled = true;
+            document.getElementById(\'testDatabaseConnectivityIndicator\').style.visibility = \'visible\';
+            Installpage_append(' . json_encode($testRequest) . ', \'Please wait while your connection is tested...\');
+            </script>';
             die();
         }
 
@@ -162,15 +169,15 @@
         }
 
         echo '
-            <script type="text/javascript">
-                setActiveStep(2);
-                showTextBlock(\'databaseConnectivity\');
-                document.getElementById(\'dbname\').value = \'' . htmlspecialchars(DATABASE_NAME) . '\';
-                document.getElementById(\'dbuser\').value = \'' . htmlspecialchars(DATABASE_USER) . '\';
-                document.getElementById(\'dbpass\').value = \'\';
-                document.getElementById(\'dbpass\').placeholder = \'' . $dbPassPlaceholder . '\';
-                document.getElementById(\'dbhost\').value = \'' . htmlspecialchars(DATABASE_HOST) . '\';
-            </script>';
+        <script type="text/javascript">
+        setActiveStep(2);
+        showTextBlock(\'databaseConnectivity\');
+        document.getElementById(\'dbname\').value = ' . json_encode(DATABASE_NAME) . ';
+        document.getElementById(\'dbuser\').value = ' . json_encode(DATABASE_USER) . ';
+        document.getElementById(\'dbpass\').value = \'\';
+        document.getElementById(\'dbpass\').placeholder = ' . json_encode($dbPassPlaceholder) . ';
+        document.getElementById(\'dbhost\').value = ' . json_encode(DATABASE_HOST) . ';
+        </script>';
         break;
 
     case 'mailSettings':
@@ -267,28 +274,68 @@
         }
         break;
 
-    case 'testDatabaseConnectivity':
-        echo '<br /><span style="font-weight: bold;">Test Results</span>';
+        case 'testDatabaseConnectivity':
+            $databaseUser = trim($_REQUEST['user'] ?? '');
+            $databasePass = $_REQUEST['pass'] ?? '';
+            $databaseHost = trim($_REQUEST['host'] ?? '');
+            $databaseName = trim($_REQUEST['name'] ?? '');
 
-        echo '<table class="test_output">';
+            echo '<br /><span style="font-weight: bold;">Test Results</span>';
+            echo '<table class="test_output">';
 
-        if (InstallationTests::checkMySQL(DATABASE_HOST, DATABASE_USER, DATABASE_PASS, DATABASE_NAME))
-        {
-            echo '<script type="text/javascript">showTextBlock(\'MySQLTestPassed\');</script>';
-        }
-        else
-        {
-            echo '<script type="text/javascript">showTextBlock(\'MySQLTestFailed\');</script>';
-        }
+            if ($databaseUser === '' || $databaseHost === '' || $databaseName === '')
+            {
+                echo '<tr class="fail"><td>Database name, user and host are required.</td></tr>';
+                $connectionPassed = false;
+            }
+            else
+            {
+                $connectionPassed = InstallationTests::checkMySQL(
+                    $databaseHost,
+                    $databaseUser,
+                    $databasePass,
+                    $databaseName
+                );
+            }
 
-        echo '</table>';
+            if ($connectionPassed)
+            {
+                /*
+                 * Only persist the database settings after they have been
+                 * successfully tested.
+                 */
+                CATSUtility::changeConfigSetting(
+                    'DATABASE_USER',
+                    var_export($databaseUser, true)
+                );
+                CATSUtility::changeConfigSetting(
+                    'DATABASE_PASS',
+                    var_export($databasePass, true)
+                );
+                CATSUtility::changeConfigSetting(
+                    'DATABASE_HOST',
+                    var_export($databaseHost, true)
+                );
+                CATSUtility::changeConfigSetting(
+                    'DATABASE_NAME',
+                    var_export($databaseName, true)
+                );
 
-        echo '
+                echo '<script type="text/javascript">showTextBlock(\'MySQLTestPassed\');</script>';
+            }
+            else
+            {
+                echo '<script type="text/javascript">showTextBlock(\'MySQLTestFailed\');</script>';
+            }
+
+            echo '</table>';
+
+            echo '
             <script type="text/javascript">
-                document.getElementById(\'testDatabaseConnectivity\').disabled = false;
-                document.getElementById(\'testDatabaseConnectivityIndicator\').style.visibility = \'hidden\';
+            document.getElementById(\'testDatabaseConnectivity\').disabled = false;
+            document.getElementById(\'testDatabaseConnectivityIndicator\').style.visibility = \'hidden\';
             </script>';
-        break;
+            break;
 
     case 'resumeParsing':
         echo '<script type="text/javascript">setActiveStep(4);</script>';
diff --git a/modules/install/phpVersion.php b/modules/install/phpVersion.php
index c877d5bd4..037ded576 100755
--- a/modules/install/phpVersion.php
+++ b/modules/install/phpVersion.php
@@ -18,9 +18,15 @@
         </div>
 
         <div id="contents">
-            <div id="login">
-                <p>Your PHP version is <?php echo phpversion(); ?>  OpenCATS Requires PHP 5 or better.</p>
-                <p>Please get a newer version of PHP and try again.</p>
+        <div id="login">
+        <p>
+        Your PHP version is
+        <?php echo htmlspecialchars(PHP_VERSION, ENT_QUOTES, 'UTF-8'); ?>.
+        OpenCATS requires PHP
+        <?php echo htmlspecialchars($minimumPHPVersion, ENT_QUOTES, 'UTF-8'); ?>
+        or newer.
+        </p>
+        <p>Please install a supported PHP version and try again.</p>
             </div>
         </div>
     </body>
