apache2 was vulnerable to IP address spoofing when proxying using mod_remoteip and mod_rewrite.
For configurations using proxying with mod_remoteip and certain mod_rewrite rules, an attacker could spoof their IP address for logging and PHP scripts.
For Debian 8 jessie, these problems have been fixed in version 2.4.10-10+deb8u17.
We recommend that you upgrade your apache2 packages.
Further information about Extended LTS security advisories can be found at: https://deb.freexian.com/extended-lts/