Suppose you are the attacker who has got hold of the complied
SimpleWebServer.class. Describe an attack such that, after
SimpleWebServer is re-started (e.g., because of an exception by
another attack), the functionality in (3) is disabled.
Simple web server.java
public class SimpleWebServer {
/* Run the HTTP server on this TCP port.
*/
private static final int PORT = 8081;
/* The socket used to process incoming
connections from web clients */
private static ServerSocket dServerSocket;
public SimpleWebServer() throws Exception
{
dServerSocket = new
ServerSocket(PORT);
}
public void run() throws Exception {
while (true) {
/* wait
for a connection from a client */
Socket s =
dServerSocket.accept();
/* then
process the client’s request */
processRequest(s);
}
}
/*
* Reads the HTTP request from the client, and
responds with the file the user
* requested or a HTTP error code.
*/
public void processRequest(Socket s) throws
Exception {
/* used to read data from the
client */
BufferedReader br = new
BufferedReader(new InputStreamReader(s.getInputStream()));
/* used to write data to
the client */
OutputStreamWriter osw = new
OutputStreamWriter(s.getOutputStream());
/* read the HTTP request
from the client */
String request =
br.readLine();
String command =
null;
String pathname = null;
/* parse the HTTP request
*/
StringTokenizer st = new
StringTokenizer(request, ” “);
command =
st.nextToken();
pathname =
st.nextToken();
if (command.equals(“GET”))
{
/*
* if the
request is a GET try to respond with the file the user is
requesting
*/
System.out.println(“Path name: ” + pathname);
serveFile(osw, pathname);
} else {
/*
* if the
request is a NOT a GET, return an error saying this server does
not
*
implement the requested command
*/
osw.write(“HTTP/1.0 501 Not Implementednn”);
}
/* close the connection to
the client */
osw.close();
}
public void serveFile(OutputStreamWriter osw,
String pathname) throws Exception {
FileReader fr = null;
int c = -1;
StringBuffer sb = new
StringBuffer();
/* remove the initial
slash at the beginning of the pathname in the request */
if (pathname.charAt(0) ==
‘/’)
pathname =
pathname.substring(1);
/*
* if there was no filename
specified by the client, serve the “index.html” file
*/
if
(pathname.equals(“”))
pathname =
“index.html”;
/* try to open file
specified by pathname */
try {
//
System.out.println(“Path name: “+pathname);
fr = new
FileReader(pathname);
c =
fr.read();
} catch (Exception e) {
/* if the
file is not found,return the appropriate HTTP response code
*/
osw.write(“HTTP/1.0 404 Not Foundnn”);
return;
}
/*
* if the requested file can
be successfully opened and read, then return an OK
* response code and send the
contents of the file
*/
osw.write(“HTTP/1.0 200
OKnn”);
while (c != -1) {
sb.append((char) c);
c =
fr.read();
}
osw.write(sb.toString());
}
/* This method is called when the program is
run from the command line. */
public static void main(String argv[]) throws
Exception {
/* Create a SimpleWebServer
object, and run it */
SimpleWebServer sws = new
SimpleWebServer();
sws.run();
}
}
