GHSA-m95x-m25c-w9mp XML-RPC for PHP allows access to local files via malicious argument to the Client::send method

Abusing the $method argument of Client::send, it was possible to force the client to access local files or connect to undesired urls instead of the intended target server's url (the one used in the Client constructor).

This weakness only affects installations where all the following conditions apply, at the same time:

• the xmlrpc Client is used, ie. not xmlrpc servers
• untrusted data (eg. data from remote users) is used as value for the $method argument of method Client::send(), in conjunction with conditions which trigger usage of curl as http transport (ie. either using the https, http11 or http2 protocols, or calling Client::setUseCurl() beforehand)
• either have set the Clients return_type property to 'xml', or make the resulting Response's object httpResponse member, which is intended to be used for debugging purposes only, available to 3rd parties, eg. by displaying it to the end user or serializing it in some storage (note that the same data can also be accessed via magic property Response::raw_data, and in the Request's httpResponse member)

This is most likely a very uncommon usage scenario, and as such the chances of exploitation of this issue may be low.

If it is not possible to upgrade to this release of the library at this time, a proactive security measure, to avoid the Client accessing any local file on the server which hosts it, is to add the following call to your code:

  $client->setCurlOptions([CURLOPT_PROTOCOLS, CURLPROTO_HTTPS|CURLPROTO_HTTP]);

Originally reported as issue #81