This update for apache2 fixes the following issues:
It used to be possible to set an arbitrary $HTTPPROXY environment variable
for request handlers -- like CGI scripts -- by including a specially crafted
HTTP header in the request (CVE-2016-5387). As a result, these server
components would potentially direct all their outgoing HTTP traffic through a
malicious proxy server. This patch fixes the issue: the updated Apache server
ignores such HTTP headers and never sets $HTTPPROXY for sub-processes
(unless a value has been explicitly configured by the administrator in the
configuration file). (bsc#988488)