The remote Debian host is missing a security-related update.
Several vulnerabilities were discovered in libgd2, a library for programmatic graphics creation and manipulation. A remote attacker can take advantage of these flaws to cause a denial-of-service against an application using the libgd2 library (application crash), or potentially to execute arbitrary code with the privileges of the user running the application.
Upgrade the libgd2 packages. For the stable distribution (jessie), these problems have been fixed in version 2.1.0-5+deb8u4.