Block files exploiting IE's mime-sniffing 'feature'

inc/config.php

@@ -120,6 +120,7 @@
 	$config['error']['invalidzip']		= 'Invalid archive!';
 	$config['error']['fileexists']		= 'That file <a href="%s">already exists</a>!';
 	$config['error']['delete_too_soon']	= 'You\'ll have to wait another %s before deleting that.';
+	$config['error']['mime_exploit']	= 'MIME type detection XSS exploit (IE) detected; post discarded.';
 	
 	// Moderator errors
 	$config['error']['invalid']			= 'Invalid username and/or password.';
@@ -476,6 +477,9 @@
 	$config['ipv6_regex']	= '((([0-9A-Fa-f]{1,4}:){7}([0-9A-Fa-f]{1,4}|:))|(([0-9A-Fa-f]{1,4}:){6}(:[0-9A-Fa-f]{1,4}|((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3})|:))|(([0-9A-Fa-f]{1,4}:){5}(((:[0-9A-Fa-f]{1,4}){1,2})|:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3})|:))|(([0-9A-Fa-f]{1,4}:){4}(((:[0-9A-Fa-f]{1,4}){1,3})|((:[0-9A-Fa-f]{1,4})?:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){3}(((:[0-9A-Fa-f]{1,4}){1,4})|((:[0-9A-Fa-f]{1,4}){0,2}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){2}(((:[0-9A-Fa-f]{1,4}){1,5})|((:[0-9A-Fa-f]{1,4}){0,3}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9A-Fa-f]{1,4}:){1}(((:[0-9A-Fa-f]{1,4}){1,6})|((:[0-9A-Fa-f]{1,4}){0,4}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(:(((:[0-9A-Fa-f]{1,4}){1,7})|((:[0-9A-Fa-f]{1,4}){0,5}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:)))(%.+)?';
 	// Make IPv4 addresses look like IPv4 addresses ("::ffff:8.8.8.8" becomes "8.8.8.8")
 	$config['ipv6_ipv4']	= true;
+	// Regular expression to check for IE MIME type detection XSS exploit. To disable, comment the line out
+	// https://github.com/savetheinternet/Tinyboard/issues/20
+	$config['ie_mime_type_detection'] = '/<(?:body|head|html|img|plaintext|pre|script|table|title|a href|channel|scriptlet)/';
 	
 	// Allowed file extensions
 	$config['allowed_ext'] = Array('jpg', 'jpeg', 'bmp', 'gif', 'png');

post.php

@@ -407,6 +407,13 @@
 				error($config['error']['maxsize']);
 			}
 			
+			// Check IE MIME type detection XSS exploit
+			$buffer = file_get_contents($post['file'], null, null, null, 255);
+			if(preg_match($config['ie_mime_type_detection'], $buffer)) {
+				undoImage($post);
+				error($config['error']['mime_exploit']);
+			}
+			
 			$post['filehash'] = $config['file_hash']($post['file']);
 			$post['filesize'] = filesize($post['file']);