SanitizationTests.java

import java.io.IOException;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class SanitizationTests extends HttpServlet {
    private static final String VALID_URI = "http://lgtm.com";
    private HttpClient client = HttpClient.newHttpClient();

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        try {

            URI uri = new URI(request.getParameter("uri")); // $ Source
            // BAD: a request parameter is incorporated without validation into a Http
            // request
            HttpRequest r = HttpRequest.newBuilder(uri).build(); // $ Alert
            client.send(r, null); // $ Alert

            // GOOD: sanitisation by concatenation with a prefix that prevents targeting an arbitrary host.
            // We test a few different ways of sanitisation: via string conctentation (perhaps nested),
            // via a stringbuilder (for which we consider appends done in the constructor, chained onto
            // the constructor and applied in subsequent statements) and via String.format.
            String safeUri3 = "https://example.com/" + request.getParameter("uri3");
            HttpRequest r3 = HttpRequest.newBuilder(new URI(safeUri3)).build();
            client.send(r3, null);

            String safeUri4 = "https://example.com/" + ("someprefix" + request.getParameter("uri4"));
            HttpRequest r4 = HttpRequest.newBuilder(new URI(safeUri4)).build();
            client.send(r4, null);

            StringBuilder safeUri5 = new StringBuilder();
            safeUri5.append("https://example.com/").append(request.getParameter("uri5"));
            HttpRequest r5 = HttpRequest.newBuilder(new URI(safeUri5.toString())).build();
            client.send(r5, null);

            StringBuilder safeUri5a = new StringBuilder("https://example.com/");
            safeUri5a.append(request.getParameter("uri5a"));
            HttpRequest r5a = HttpRequest.newBuilder(new URI(safeUri5a.toString())).build();
            client.send(r5a, null);

            StringBuilder safeUri5b = (new StringBuilder("https://example.com/")).append("dir/");
            safeUri5b.append(request.getParameter("uri5b"));
            HttpRequest r5b = HttpRequest.newBuilder(new URI(safeUri5b.toString())).build();
            client.send(r5b, null);

            StringBuilder safeUri5c = (new StringBuilder("prefix")).append("https://example.com/dir/");
            safeUri5c.append(request.getParameter("uri5c"));
            HttpRequest r5c = HttpRequest.newBuilder(new URI(safeUri5c.toString())).build();
            client.send(r5c, null);

            String safeUri6 = String.format("https://example.com/%s", request.getParameter("uri6"));
            HttpRequest r6 = HttpRequest.newBuilder(new URI(safeUri6)).build();
            client.send(r6, null);

            String safeUri7 = String.format("%s/%s", "https://example.com", request.getParameter("uri7"));
            HttpRequest r7 = HttpRequest.newBuilder(new URI(safeUri7)).build();
            client.send(r7, null);

            String safeUri8 = String.format("%s%s", "https://example.com/", request.getParameter("uri8"));
            HttpRequest r8 = HttpRequest.newBuilder(new URI(safeUri8)).build();
            client.send(r8, null);

            String safeUri9 = String.format("http://%s", "myserver.com") + "/" + request.getParameter("uri9");
            HttpRequest r9 = HttpRequest.newBuilder(new URI(safeUri9)).build();
            client.send(r9, null);

            // BAD: cases where a string that would sanitise is used, but occurs in the wrong
            // place to sanitise user input:
            String unsafeUri3 = request.getParameter("baduri3") + "https://example.com/"; // $ Source
            HttpRequest unsafer3 = HttpRequest.newBuilder(new URI(unsafeUri3)).build();  // $ Alert
            client.send(unsafer3, null); // $ Alert

            String unsafeUri4 = ("someprefix" + request.getParameter("baduri4")) + "https://example.com/"; // $ Source
            HttpRequest unsafer4 = HttpRequest.newBuilder(new URI(unsafeUri4)).build(); // $ Alert
            client.send(unsafer4, null); // $ Alert

            StringBuilder unsafeUri5 = new StringBuilder();
            unsafeUri5.append(request.getParameter("baduri5")).append("https://example.com/"); // $ Source
            HttpRequest unsafer5 = HttpRequest.newBuilder(new URI(unsafeUri5.toString())).build(); // $ Alert
            client.send(unsafer5, null); // $ Alert

            StringBuilder unafeUri5a = new StringBuilder(request.getParameter("uri5a")); // $ Source
            unafeUri5a.append("https://example.com/");
            HttpRequest unsafer5a = HttpRequest.newBuilder(new URI(unafeUri5a.toString())).build(); // $ Alert
            client.send(unsafer5a, null); // $ Alert

            StringBuilder unsafeUri5b = (new StringBuilder(request.getParameter("uri5b"))).append("dir/"); // $ Source
            unsafeUri5b.append("https://example.com/");
            HttpRequest unsafer5b = HttpRequest.newBuilder(new URI(unsafeUri5b.toString())).build(); // $ Alert
            client.send(unsafer5b, null); // $ Alert

            StringBuilder unsafeUri5c = (new StringBuilder("https")).append(request.getParameter("uri5c")); // $ Source
            unsafeUri5c.append("://example.com/dir/");
            HttpRequest unsafer5c = HttpRequest.newBuilder(new URI(unsafeUri5c.toString())).build(); // $ Alert
            client.send(unsafer5c, null); // $ Alert

            String unsafeUri6 = String.format("%shttps://example.com/", request.getParameter("baduri6")); // $ Source
            HttpRequest unsafer6 = HttpRequest.newBuilder(new URI(unsafeUri6)).build(); // $ Alert
            client.send(unsafer6, null); // $ Alert

            String unsafeUri7 = String.format("%s/%s", request.getParameter("baduri7"), "https://example.com"); // $ Source
            HttpRequest unsafer7 = HttpRequest.newBuilder(new URI(unsafeUri7)).build(); // $ Alert
            client.send(unsafer7, null); // $ Alert

            String unsafeUri8 = String.format("%s%s", request.getParameter("baduri8"), "https://example.com/"); // $ Source
            HttpRequest unsafer8 = HttpRequest.newBuilder(new URI(unsafeUri8)).build(); // $ Alert
            client.send(unsafer8, null); // $ Alert

            String unsafeUri9 = request.getParameter("baduri9") + "/" + String.format("http://%s", "myserver.com"); // $ Source
            HttpRequest unsafer9 = HttpRequest.newBuilder(new URI(unsafeUri9)).build(); // $ Alert
            client.send(unsafer9, null); // $ Alert

            String unsafeUri10 = String.format("%s://%s:%s%s", "http", "myserver.com", "80", request.getParameter("baduri10")); // $ Source
            HttpRequest unsafer10 = HttpRequest.newBuilder(new URI(unsafeUri10)).build(); // $ Alert
            client.send(unsafer10, null); // $ Alert

            // GOOD: sanitisation by regexp validation
            String param10 = request.getParameter("uri10");
            if (param10.matches("[a-zA-Z0-9_-]+")) {
                HttpRequest r10 = HttpRequest.newBuilder(new URI(param10)).build();
                client.send(r10, null);
            }
            
            String param11 = request.getParameter("uri11");
            validate(param11);
            HttpRequest r11 = HttpRequest.newBuilder(new URI(param11)).build();
            client.send(r11, null);
        } catch (Exception e) {
            // TODO: handle exception
        }
    }

    private void validate(String s) {
        if (!s.matches("[a-zA-Z0-9_-]+")) {
            throw new IllegalArgumentException("Invalid ID");
        }
    }
}