Insufficient data authenticity validation - Checksum verification
Need
Enhanced data authenticity validation and checksum verification
Context
- Usage of Java 8 for developing applications with enhanced features and performance
- Usage of javax.servlet-api for developing Java web applications with Servlets
- Usage of java.net for network communication in Java
Description
Non compliant code
import javax.servlet.http.*;
import java.io.*;
import java.net.*;
public class VulnerableServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
String externalResource = request.getParameter("resource");
URL url = new URL(externalResource);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
String inputLine;
StringBuffer content = new StringBuffer();
while ((inputLine = in.readLine()) != null) {
content.append(inputLine);
}
in.close();
connection.disconnect();
response.getWriter().write(content.toString());
}
}
The above code is a simple servlet that accepts a URL as a parameter and attempts to retrieve the resource at that URL. It then writes the content of the resource to the HTTP response.
The vulnerability lies in the fact that the servlet does not validate the integrity of the received resource. This means that an attacker could potentially manipulate the resource on the external server, and the servlet would still serve the manipulated resource to its users.
For example, if the external resource is a JavaScript file, an attacker could add malicious code to the file on the external server. When the servlet retrieves the file and serves it to its users, the users' browsers would execute the malicious code.
This is a serious vulnerability as it allows an attacker to execute arbitrary code in the users' browsers. This could lead to a variety of attacks, such as stealing sensitive information (like session cookies) or performing actions on behalf of the user.
The root cause of this vulnerability is the lack of checksum verification. A checksum is a value that is computed from the data in a file. If the file changes, the checksum also changes. By comparing the checksum of the received resource with a previously computed checksum, the servlet could detect if the resource has been manipulated. However, the above code does not perform this check, which is why it is vulnerable.
Steps
- Implement data authenticity validation by verifying the integrity of resources loaded from external servers.
- Use a secure method to validate the checksum or hash of the received data.
- Compare the calculated checksum or hash with the expected value to ensure data integrity.
- If the checksum or hash does not match the expected value, reject the resource and handle the error appropriately.
- Consider using secure protocols (e.g., HTTPS) for communication with external servers to prevent man-in-the-middle attacks.
- Regularly update and patch the application to address any security vulnerabilities in the libraries or frameworks used.
Compliant code
import javax.servlet.http.*;
import java.io.*;
import java.net.*;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;
public class SecureServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, NoSuchAlgorithmException {
String externalResource = request.getParameter("resource");
URL url = new URL(externalResource);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
// Calculate the checksum of the received data
MessageDigest md = MessageDigest.getInstance("SHA-256");
InputStream is = connection.getInputStream();
byte[] dataBytes = new byte[1024];
int nread = 0;
while ((nread = is.read(dataBytes)) != -1) {
md.update(dataBytes, 0, nread);
}
byte[] mdbytes = md.digest();
// Convert the byte to hex format
StringBuffer sb = new StringBuffer();
for (int i = 0; i < mdbytes.length; i++) {
sb.append(Integer.toString((mdbytes[i] & 0xff) + 0x100, 16).substring(1));
}
// Compare the calculated checksum with the expected value
String expectedChecksum = "EXPECTED_CHECKSUM"; // This should be replaced with the actual expected checksum
if (!sb.toString().equals(expectedChecksum)) {
// Handle the error appropriately
response.getWriter().write("Checksum verification failed. The resource is rejected.");
return;
}
// If the checksum verification is successful, process the data
BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
String inputLine;
StringBuffer content = new StringBuffer();
while ((inputLine = in.readLine()) != null) {
content.append(inputLine);
}
in.close();
connection.disconnect();
response.getWriter().write(content.toString());
}
}
The above code fixes the vulnerability of insufficient data authenticity validation by implementing checksum verification.
Firstly, it calculates the checksum of the received data using SHA-256 algorithm. The MessageDigest class is used to calculate the message digest algorithm, and the InputStream is used to read the data from the connection.
Then, it converts the calculated checksum (which is in byte format) to hex format for comparison.
Next, it compares the calculated checksum with the expected value. If the checksums do not match, it means that the data integrity is compromised. In this case, the code handles the error by sending a response to the client indicating that the checksum verification failed and the resource is rejected.
If the checksum verification is successful, it means that the data integrity is maintained. In this case, the code processes the data as usual.
This code also recommends using secure protocols (e.g., HTTPS) for communication with external servers to prevent man-in-the-middle attacks, and regularly updating and patching the application to address any security vulnerabilities in the libraries or frameworks used.