The SimpleSAML_XML_Validator class constructor in SimpleSAMLphp before 1.14.11 might allow remote attackers to spoof signatures on SAML 1 responses or possibly cause a denial of service (memory consumption) by leveraging improper conversion of return values to boolean.
https://simplesamlphp.org/security/201612-02
https://lists.debian.org/debian-lts-announce/2018/03/msg00001.html