It was discovered that there was a potential arbitrary code execution vulnerability in Velocity, a Java-based template engine for writing web applications. It could be exploited by applications which allowed untrusted users to upload/modify templates.
For Debian 8 Jessie, these problems have been fixed in version 1.7-4+deb8u1.
We recommend that you upgrade your velocity packages.
Further information about Extended LTS security advisories can be found at: https://deb.freexian.com/extended-lts/