The remote Debian host is missing a security-related update.
Kelby Ludwig and Scott Cantor discovered that the Shibboleth service provider is vulnerable to impersonation attacks and information disclosure due to incorrect XML parsing. For additional details please refer to the upstream advisory at https://shibboleth.net/community/advisories/secadv_20180227.txt
Upgrade the xmltooling packages. For the oldstable distribution (jessie), this problem has been fixed in version 1.5.3-2+deb8u3. For the stable distribution (stretch), this problem has been fixed in version 1.6.0-4+deb9u1.