Fix weak CSRF nonce in CSRF Challenge Six Target

src/main/java/servlets/module/challenge/CsrfChallengeSixGetToken.java

@@ -69,7 +69,12 @@ public void doGet(HttpServletRequest request, HttpServletResponse response)
       if (Validate.validateSession(ses)) {
         log.debug(levelName + " servlet accessed by: " + ses.getAttribute("userName").toString());
         String htmlOutput = new String("Your csrf Token for this Challenge is: ");
-        String userId = request.getParameter("userId").toString();
+        // The userId must be the caller's own - taking it from a request parameter let any
+        // authenticated user fetch any other user's real CSRF token directly, and the LIKE
+        // match (with wildcard metacharacters left unescaped) made it worse by allowing broad
+        // token disclosure. This defeats the point of the token being unguessable, since the
+        // whole defense relies on an attacker being unable to learn the victim's value.
+        String userId = (String) ses.getAttribute("userStamp");
 
         Connection conn =
             Database.getChallengeConnection(
@@ -78,7 +83,7 @@ public void doGet(HttpServletRequest request, HttpServletResponse response)
           log.debug("Preparing setCsrfChallengeSixToken call");
           PreparedStatement callstmnt =
               conn.prepareStatement(
-                  "SELECT csrfTokenscol FROM csrfchallengesix.csrfTokens WHERE userId LIKE ?");
+                  "SELECT csrfTokenscol FROM csrfchallengesix.csrfTokens WHERE userId = ?");
           callstmnt.setString(1, userId);
           log.debug("Executing setCsrfChallengeSixTokenQuery");
           ResultSet rs = callstmnt.executeQuery();

src/main/java/servlets/module/challenge/CsrfChallengeTargetSix.java

@@ -5,7 +5,6 @@
 import java.io.IOException;
 import java.io.PrintWriter;
 import java.util.Locale;
-import java.util.Random;
 import java.util.ResourceBundle;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
@@ -14,6 +13,7 @@
 import javax.servlet.http.HttpSession;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
+import utils.Hash;
 import utils.ShepherdLogManager;
 import utils.Validate;
 
@@ -42,11 +42,6 @@ public class CsrfChallengeTargetSix extends HttpServlet {
   private static final long serialVersionUID = 1L;
   private static String moduleHash =
       "2fff41105149e507c75b5a54e558470469d7024929cf78d570cd16c03bee3569";
-  private static final String[] csrfArray = {
-    "c4ca4238a0b923820dcc509a6f75849b",
-    "c81e728d9d4c2f636f067f89cc14862c",
-    "eccbc87e4b5ce2fe28308fd9f2a7baf3"
-  };
   private static final Logger log = LogManager.getLogger(CsrfChallengeTargetSix.class);
   private static String levelName = "CSRF 6 Target";
 
@@ -85,9 +80,11 @@ public void doPost(HttpServletRequest request, HttpServletResponse response)
         if (ses.getAttribute(csrfTokenName) == null
             || ses.getAttribute(csrfTokenName).toString().isEmpty()) {
           log.debug("No CSRF Token associated with user");
-          Random random = new Random();
-          int newToken = random.nextInt(3);
-          storedToken = csrfArray[newToken];
+          // random.nextInt(3) as an index into a 3-element array only ever produces one of 3
+          // possible values, letting an attacker brute-force a valid nonce in at most 3 tries
+          // without ever touching the victim's session. Hash.randomString() matches the
+          // real-random pattern used elsewhere.
+          storedToken = Hash.randomString();
           out.write(
               csrfGenerics.getString("target.noTokenNewToken") + " " + storedToken + "<br><br>");
           ses.setAttribute(csrfTokenName, storedToken);