diff --git a/src/etc/inc/util.inc b/src/etc/inc/util.inc
index a0b126fc34..30744ec4fa 100644
--- a/src/etc/inc/util.inc
+++ b/src/etc/inc/util.inc
@@ -2907,4 +2907,25 @@ function dhcpd_date_adjust_gmt($dt) {
 	return $dt;
 }
 
+global $supported_image_types;
+$supported_image_types = array(
+	IMAGETYPE_JPEG,
+	IMAGETYPE_PNG,
+	IMAGETYPE_GIF,
+	IMAGETYPE_WEBP
+);
+
+function is_supported_image($image_filename) {
+	global $supported_image_types;
+	$img_info = getimagesize($image_filename);
+
+	/* If it's not an image, or it isn't in the supported list, return false */
+	if (($img_info === false) ||
+	    !in_array($img_info[2], array_keys($supported_image_types))) {
+		return false;
+	} else {
+		return $img_info[2];
+	}
+}
+
 ?>
diff --git a/src/usr/local/www/services_captiveportal.php b/src/usr/local/www/services_captiveportal.php
index 431b2ed905..e497fc96cf 100644
--- a/src/usr/local/www/services_captiveportal.php
+++ b/src/usr/local/www/services_captiveportal.php
@@ -311,6 +311,14 @@ if ($_POST['save']) {
 	if (trim($_POST['radiusnasid']) !== "" && !preg_match("/^[\x21-\x7e]{3,253}$/i", trim($_POST['radiusnasid']))) {
 		$input_errors[] = gettext("The NAS-Identifier must be 3-253 characters long and should only contain ASCII characters.");
 	}
+	if (is_uploaded_file($_FILES['logo-img']['tmp_name']) &&
+	    (is_supported_image($_FILES['logo-img']['tmp_name']) === false)) {
+		$input_errors[] = gettext("Unsupported logo image type.");
+	}
+	if (is_uploaded_file($_FILES['background-img']['tmp_name']) &&
+	    (is_supported_image($_FILES['background-img']['tmp_name']) === false)) {
+		$input_errors[] = gettext("Unsupported background image type.");
+	}
 
 	if (!$input_errors) {
 		init_config_arr(array('captiveportal', $cpzone));
@@ -426,8 +434,9 @@ if ($_POST['save']) {
 
 		// Check for uploaded images for the default CP login
 		if (is_uploaded_file($_FILES['logo-img']['tmp_name'])) {
-			$ext = pathinfo($_FILES['logo-img']['name'],PATHINFO_EXTENSION);
-			$logo_name = "captiveportal-logo." . $ext;
+
+			/* Validated above, so returned value is OK */
+			$logo_name = "captiveportal-logo." . image_type_to_extension(is_supported_image($_FILES['logo-img']['tmp_name']));
 			for ($i = 0; $i < count($a_cp[$cpzone]['element']); $i++) {
 				if (strpos($a_cp[$cpzone]['element'][$i]['name'], "captiveportal-logo.") !== false){
 					// remove old image before replacing it.
@@ -447,8 +456,8 @@ if ($_POST['save']) {
 			move_uploaded_file( $_FILES['logo-img']['tmp_name'], $target);
 		}
 		if (is_uploaded_file($_FILES['background-img']['tmp_name'])) {
-			$ext = pathinfo($_FILES['background-img']['name'],PATHINFO_EXTENSION);
-			$background_name = "captiveportal-background." . $ext;
+			/* Validated above, so returned value is OK */
+			$background_name = "captiveportal-background." . image_type_to_extension(is_supported_image($_FILES['background-img']['tmp_name']));
 			// is there already a file with that name?
 			for ($i = 0; $i < count($a_cp[$cpzone]['element']); $i++) {
 				if (strpos($a_cp[$cpzone]['element'][$i]['name'], "captiveportal-background.") !== false){
diff --git a/src/usr/local/www/widgets/widgets/picture.widget.php b/src/usr/local/www/widgets/widgets/picture.widget.php
index 0db1a93804..3723fb394f 100644
--- a/src/usr/local/www/widgets/widgets/picture.widget.php
+++ b/src/usr/local/www/widgets/widgets/picture.widget.php
@@ -38,20 +38,9 @@ if ($_GET['getpic']=="true") {
 	}
 
 	/* Do not rely on filename to determine image type. */
-	$img_info =getimagesize($image_filename);
-	switch ($img_info[2]) {
-		case IMAGETYPE_GIF:
-			$pic_type = "gif";
-			break;
-		case IMAGETYPE_JPEG:
-			$pic_type = "jpg";
-			break;
-		case IMAGETYPE_PNG:
-			$pic_type = "png";
-			break;
-		default:
-			echo null;
-			exit;
+	$pic_type = is_supported_image($image_filename);
+	if (empty($pic_type)) {
+		exit;
 	}
 
 	if ($user_settings['widgets'][$wk]['picturewidget']) {
@@ -63,7 +52,7 @@ if ($_GET['getpic']=="true") {
 	}
 
 	header("Content-Disposition: inline; filename=\"" . basename($image_filename) . "\"");
-	header("Content-Type: image/{$pic_type}");
+	header("Content-Type: " . image_type_to_mime_type($pic_type));
 	header("Content-Length: " . strlen($data));
 	echo $data;
 	exit;
@@ -88,12 +77,8 @@ if ($_POST['widgetkey']) {
 				die("Could not read temporary file");
 			} else {
 				// Make sure they upload an image and not some other file
-				$img_info =getimagesize($_FILES['pictfile']['tmp_name']);
-				if($img_info === FALSE){
-					die("Unable to determine image type of uploaded file");
-				}
-				if(($img_info[2] !== IMAGETYPE_GIF) && ($img_info[2] !== IMAGETYPE_JPEG) && ($img_info[2] !== IMAGETYPE_PNG)){
-					die("Not a gif/jpg/png");
+				if (!is_supported_image($_FILES['pictfile']['tmp_name'])) {
+					die("Not a supported image type");
 				}
 				$picname = basename($_FILES['uploadedfile']['name']);
 				$user_settings['widgets'][$wk]['picturewidget'] = "/conf/widget_image";