php-saml-sp before 1.1.1 and 2.x before 2.1.1 allows reading arbitrary files as the webserver user because resolving XML external entities was silently enabled via \LIBXML_DTDLOAD | \LIBXML_DTDATTR.
The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.