This attack consists in changing resources identifiers used by application in order to perform malicious task. When an application permits a user input to define a resource, like file name or port number, this data can be manipulated to execute or access different resources.
In order to be properly executed, the attacker must have the possibility to specify a resource identifier thru application form and the application must permit its execution.
The resource type affected by user input indicates the content type that may be exposed. For example, an application that permits input of special characters like period, slash, and backslash are risky when used in methods that interact with the file system.
The resource injection attack focus on accessing other resources than local filesystem, whose is done thru a different attack technique known as Path Manipulation attack.
The following examples represent an application which gets a port number from HTTP request and create a socket with this port number without any validation. A user using a proxy can modify this port and obtain a direct connection (socket) with the server.
String rPort = request.getParameter("remotePort"); ... ServerSocket srvr = new ServerSocket(rPort); Socket skt = srvr.accept(); ...
int rPort = Int32.Parse(Request.get_Item("remotePort ")); ... IPEndPoint endpoint = new IPEndPoint(address,rPort); socket = new Socket(endpoint.AddressFamily, SocketType.Stream, ProtocolType.Tcp); socket.Connect(endpoint); ...
This example is same as previous, but it gets port number from CGI requests using C++:
char* rPort = getenv("remotePort "); ... serv_addr.sin_port = htons(atoi(rPort)); if (connect(sockfd,&serv_addr,sizeof(serv_addr)) < 0) error("ERROR connecting"); ...
This example in PLSQL / TSQL gets a URL path from a CGI and downloads the file contained on it. If a user modify the path or filename it’s possible to download arbitrary files from server:
... filename := SUBSTR(OWA_UTIL.get_cgi_env('PATH_INFO'), 2); WPG_DOCLOAD.download_file(filename); ...
G. Hoglund and G. McGraw. Exploiting Software. Addison-Wesley, 2004.