The Apache HTTP Server through 2.4.23 follows RFC 3875 section 4.1.18 and therefore does not protect applications from the presence of untrusted client data in the HTTP_PROXY environment variable, which might allow remote attackers to redirect an application's outbound HTTP traffic to an arbitrary proxy server via a crafted Proxy header in an HTTP request, aka an httpoxy issue. NOTE: the vendor states This mitigation has been assigned the identifier CVE-2016-5387; in other words, this is not a CVE ID for a vulnerability. http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-5387
