1 files changed, 13 insertions, 1 deletions
diff --git a/lib/private/helper.php b/lib/private/helper.php
index 64da1f6fb12..1883ae2a8f2 100644
--- a/lib/private/helper.php
+++ b/lib/private/helper.php
@@ -733,9 +733,21 @@ class OC_Helper {
 	 * @return bool
 	 */
 	public static function issubdirectory($sub, $parent) {
-		if (strpos(realpath($sub), realpath($parent)) === 0) {
+		$realpathSub = realpath($sub);
+		$realpathParent = realpath($parent);
+
+		// realpath() may return false in case the directory does not exist
+		// since we can not be sure how different PHP versions may behave here
+		// we do an additional check whether realpath returned false
+		if($realpathSub === false ||  $realpathParent === false) {
+			return false;
+		}
+
+		// Check whether $sub is a subdirectory of $parent
+		if (strpos($realpathSub, $realpathParent) === 0) {
 			return true;
 		}
+
 		return false;
 	}