CVE-2016-5387: High severity Apple macOS High Sierra vulnerability

apache. Multiple issues were addressed by updating to version 2.4.27.

Dominic Scheirlinck of VendHQ reports:

Many software projects and vendors have implemented support for the “Proxy” request header in their respective CGI implementations and languages by creating the “HTTPPROXY” environmental variable based on the header value. When this variable is used (in many cases automatically by various HTTP client libraries) any outgoing requests generated in turn from the attackers original request can be redirected to an attacker controlled proxy. This allows attackers to view potentially sensitive information, reply with malformed data, or to hold connections open causing a potential denial of service.

The Apache HTTPD server sets various environmental variables based on headers that can then be used in CGI scripts (e.g. via modcgi). If passed a “Proxy” header in the request Apache will automatically populate the HTTPPROXY environmental variable with whatever user supplied value is present.

— Red Hat

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 HTTPPROXY 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.

— MITRE