diff --git a/mod/bookmarklet.php b/mod/bookmarklet.php
index 21b2039c58..e1ae9aa64c 100644
--- a/mod/bookmarklet.php
+++ b/mod/bookmarklet.php
@@ -30,6 +30,10 @@ function bookmarklet_content(App $a)
 	$page = normalise_link(System::baseUrl() . "/bookmarklet");
 
 	if (!strstr($referer, $page)) {
+		if (empty($_REQUEST["url"])) {
+			System::httpExit(400, ["title" => L10n::t('Bad Request')]);
+		}
+
 		$content = add_page_info($_REQUEST["url"]);
 
 		$x = [
diff --git a/mod/photos.php b/mod/photos.php
index 16af455997..e205d72c6d 100644
--- a/mod/photos.php
+++ b/mod/photos.php
@@ -212,7 +212,7 @@ function photos_post(App $a)
 		}
 
 		// Check if the user has responded to a delete confirmation query
-		if ($_REQUEST['canceled']) {
+		if (!empty($_REQUEST['canceled'])) {
 			goaway($_SESSION['photo_return']);
 		}
 
@@ -762,12 +762,14 @@ function photos_post(App $a)
 		$filesize = $ret['filesize'];
 		$type     = $ret['type'];
 		$error    = UPLOAD_ERR_OK;
-	} else {
+	} elseif (!empty($_FILES['userfile'])) {
 		$src      = $_FILES['userfile']['tmp_name'];
 		$filename = basename($_FILES['userfile']['name']);
 		$filesize = intval($_FILES['userfile']['size']);
 		$type     = $_FILES['userfile']['type'];
 		$error    = $_FILES['userfile']['error'];
+	} else {
+		$error    = UPLOAD_ERR_NO_FILE;
 	}
 
 	if ($error !== UPLOAD_ERR_OK) {
diff --git a/mod/salmon.php b/mod/salmon.php
index d07b06004d..bd4b3773cb 100644
--- a/mod/salmon.php
+++ b/mod/salmon.php
@@ -41,14 +41,14 @@ function salmon_post(App $a, $xml = '') {
 	$base = null;
 
 	// figure out where in the DOM tree our data is hiding
-	if($dom->provenance->data)
+	if (!empty($dom->provenance->data))
 		$base = $dom->provenance;
-	elseif($dom->env->data)
+	elseif (!empty($dom->env->data))
 		$base = $dom->env;
-	elseif($dom->data)
+	elseif (!empty($dom->data))
 		$base = $dom;
 
-	if(! $base) {
+	if (empty($base)) {
 		logger('unable to locate salmon data in xml ');
 		System::httpExit(400);
 	}
diff --git a/mod/webfinger.php b/mod/webfinger.php
index 6f49a8f28c..4f23db6d8f 100644
--- a/mod/webfinger.php
+++ b/mod/webfinger.php
@@ -23,7 +23,7 @@ function webfinger_content(App $a)
 	$o  = '<h3>Webfinger Diagnostic</h3>';
 
 	$o .= '<form action="webfinger" method="get">';
-	$o .= 'Lookup address: <input type="text" style="width: 250px;" name="addr" value="' . $_GET['addr'] .'" />';
+	$o .= 'Lookup address: <input type="text" style="width: 250px;" name="addr" value="' . defaults($_GET, 'addr', '') .'" />';
 	$o .= '<input type="submit" name="submit" value="Submit" /></form>';
 
 	$o .= '<br /><br />';
diff --git a/src/Model/Profile.php b/src/Model/Profile.php
index 29bc7e680d..3a014517da 100644
--- a/src/Model/Profile.php
+++ b/src/Model/Profile.php
@@ -361,7 +361,7 @@ class Profile
 			if ($r) {
 				$remote_url = $r[0]['url'];
 				$message_path = preg_replace('=(.*)/profile/(.*)=ism', '$1/message/new/', $remote_url);
-				$wallmessage_link = $message_path . base64_encode($profile['addr']);
+				$wallmessage_link = $message_path . base64_encode(defaults($profile, 'addr', ''));
 			} else if (!empty($profile['nickname'])) {
 				$wallmessage_link = 'wallmessage/' . $profile['nickname'];
 			}
diff --git a/src/Network/Probe.php b/src/Network/Probe.php
index af2d1c9a16..75231f44ff 100644
--- a/src/Network/Probe.php
+++ b/src/Network/Probe.php
@@ -967,23 +967,23 @@ class Probe
 		$hcard_url = "";
 		$data = [];
 		foreach ($webfinger["links"] as $link) {
-			if (($link["rel"] == NAMESPACE_DFRN) && ($link["href"] != "")) {
+			if (($link["rel"] == NAMESPACE_DFRN) && !empty($link["href"])) {
 				$data["network"] = Protocol::DFRN;
-			} elseif (($link["rel"] == NAMESPACE_FEED) && ($link["href"] != "")) {
+			} elseif (($link["rel"] == NAMESPACE_FEED) && !empty($link["href"])) {
 				$data["poll"] = $link["href"];
-			} elseif (($link["rel"] == "http://webfinger.net/rel/profile-page") && ($link["type"] == "text/html") && ($link["href"] != "")) {
+			} elseif (($link["rel"] == "http://webfinger.net/rel/profile-page") && (defaults($link, "type", "") == "text/html") && !empty($link["href"])) {
 				$data["url"] = $link["href"];
-			} elseif (($link["rel"] == "http://microformats.org/profile/hcard") && ($link["href"] != "")) {
+			} elseif (($link["rel"] == "http://microformats.org/profile/hcard") && !empty($link["href"])) {
 				$hcard_url = $link["href"];
-			} elseif (($link["rel"] == NAMESPACE_POCO) && ($link["href"] != "")) {
+			} elseif (($link["rel"] == NAMESPACE_POCO) && !empty($link["href"])) {
 				$data["poco"] = $link["href"];
-			} elseif (($link["rel"] == "http://webfinger.net/rel/avatar") && ($link["href"] != "")) {
+			} elseif (($link["rel"] == "http://webfinger.net/rel/avatar") && !empty($link["href"])) {
 				$data["photo"] = $link["href"];
-			} elseif (($link["rel"] == "http://joindiaspora.com/seed_location") && ($link["href"] != "")) {
+			} elseif (($link["rel"] == "http://joindiaspora.com/seed_location") && !empty($link["href"])) {
 				$data["baseurl"] = trim($link["href"], '/');
-			} elseif (($link["rel"] == "http://joindiaspora.com/guid") && ($link["href"] != "")) {
+			} elseif (($link["rel"] == "http://joindiaspora.com/guid") && !empty($link["href"])) {
 				$data["guid"] = $link["href"];
-			} elseif (($link["rel"] == "diaspora-public-key") && ($link["href"] != "")) {
+			} elseif (($link["rel"] == "diaspora-public-key") && !empty($link["href"])) {
 				$data["pubkey"] = base64_decode($link["href"]);
 
 				//if (strstr($data["pubkey"], 'RSA ') || ($link["type"] == "RSA"))
@@ -1170,21 +1170,21 @@ class Probe
 		$hcard_url = "";
 		$data = [];
 		foreach ($webfinger["links"] as $link) {
-			if (($link["rel"] == "http://microformats.org/profile/hcard") && ($link["href"] != "")) {
+			if (($link["rel"] == "http://microformats.org/profile/hcard") && !empty($link["href"])) {
 				$hcard_url = $link["href"];
-			} elseif (($link["rel"] == "http://joindiaspora.com/seed_location") && ($link["href"] != "")) {
+			} elseif (($link["rel"] == "http://joindiaspora.com/seed_location") && !empty($link["href"])) {
 				$data["baseurl"] = trim($link["href"], '/');
-			} elseif (($link["rel"] == "http://joindiaspora.com/guid") && ($link["href"] != "")) {
+			} elseif (($link["rel"] == "http://joindiaspora.com/guid") && !empty($link["href"])) {
 				$data["guid"] = $link["href"];
-			} elseif (($link["rel"] == "http://webfinger.net/rel/profile-page") && ($link["type"] == "text/html") && ($link["href"] != "")) {
+			} elseif (($link["rel"] == "http://webfinger.net/rel/profile-page") && (defaults($link, "type", "") == "text/html") && !empty($link["href"])) {
 				$data["url"] = $link["href"];
-			} elseif (($link["rel"] == NAMESPACE_FEED) && ($link["href"] != "")) {
+			} elseif (($link["rel"] == NAMESPACE_FEED) && !empty($link["href"])) {
 				$data["poll"] = $link["href"];
-			} elseif (($link["rel"] == NAMESPACE_POCO) && ($link["href"] != "")) {
+			} elseif (($link["rel"] == NAMESPACE_POCO) && !empty($link["href"])) {
 				$data["poco"] = $link["href"];
-			} elseif (($link["rel"] == "salmon") && ($link["href"] != "")) {
+			} elseif (($link["rel"] == "salmon") && !empty($link["href"])) {
 				$data["notify"] = $link["href"];
-			} elseif (($link["rel"] == "diaspora-public-key") && ($link["href"] != "")) {
+			} elseif (($link["rel"] == "diaspora-public-key") && !empty($link["href"])) {
 				$data["pubkey"] = base64_decode($link["href"]);
 
 				//if (strstr($data["pubkey"], 'RSA ') || ($link["type"] == "RSA"))
@@ -1272,15 +1272,15 @@ class Probe
 		if (is_array($webfinger["links"])) {
 			foreach ($webfinger["links"] as $link) {
 				if (($link["rel"] == "http://webfinger.net/rel/profile-page")
-					&& ($link["type"] == "text/html")
+					&& (defaults($link, "type", "") == "text/html")
 					&& ($link["href"] != "")
 				) {
 					$data["url"] = $link["href"];
-				} elseif (($link["rel"] == "salmon") && ($link["href"] != "")) {
+				} elseif (($link["rel"] == "salmon") && !empty($link["href"])) {
 					$data["notify"] = $link["href"];
-				} elseif (($link["rel"] == NAMESPACE_FEED) && ($link["href"] != "")) {
+				} elseif (($link["rel"] == NAMESPACE_FEED) && !empty($link["href"])) {
 					$data["poll"] = $link["href"];
-				} elseif (($link["rel"] == "magic-public-key") && ($link["href"] != "")) {
+				} elseif (($link["rel"] == "magic-public-key") && !empty($link["href"])) {
 					$pubkey = $link["href"];
 
 					if (substr($pubkey, 0, 5) === 'data:') {
@@ -1436,7 +1436,7 @@ class Probe
 		$data = [];
 		foreach ($webfinger["links"] as $link) {
 			if (($link["rel"] == "http://webfinger.net/rel/profile-page")
-				&& ($link["type"] == "text/html")
+				&& (defaults($link, "type", "") == "text/html")
 				&& ($link["href"] != "")
 			) {
 				$data["url"] = $link["href"];
diff --git a/src/Protocol/PortableContact.php b/src/Protocol/PortableContact.php
index 20ee77a07c..2939f69e55 100644
--- a/src/Protocol/PortableContact.php
+++ b/src/Protocol/PortableContact.php
@@ -1157,9 +1157,9 @@ class PortableContact
 
 				if (isset($data['version'])) {
 					$platform = "Mastodon";
-					$version = $data['version'];
-					$site_name = $data['title'];
-					$info = $data['description'];
+					$version = defaults($data, 'version', '');
+					$site_name = defaults($data, 'title', '');
+					$info = defaults($data, 'description', '');
 					$network = Protocol::OSTATUS;
 				}