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XS-Leaks

Description​

It is possible to use browser side-channels to obtain sensitive information from the users.

Impact​

  • Know the step in which the user is at a given moment.
  • Leak sensitive data of the user without authorization.

Recommendation​

Load the same amount of frames in all application load cases.

Threat​

Anonymous attacker from the Internet.

Expected Remediation Time​

⌚ 30 minutes.

Score​

Default score using CVSS 3.1. It may change depending on the context of the vulnerability.

Base​

  • Attack vector: N
  • Attack complexity: L
  • Privileges required: N
  • User interaction: R
  • Scope: U
  • Confidentiality: L
  • Integrity: N
  • Availability: N

Temporal​

  • Exploit code madurity: X
  • Remediation level: X
  • Report confidence: X

Result​

  • Vector string: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N/E:X/RL:X/RC:X
  • Score:
    • Base: 4.3
    • Temporal: 4.3
  • Severity:
    • Base: Medium
    • Temporal: Medium

Code Examples​

Compliant code​

The application defines the same timing frame functions without distinguishing outcomes of queries

public static void main(String[] args) {
  Scanner input = new Scanner(System.in);
  String username;
  String password;
  username = input.next();
  password = input.next();

  try {
    if(username.equals(username) && password.equals(password)){
      ScheduledExecutorService executor = Executors.newScheduledThreadPool(2);
      executor.schedule(new Runnable(){
        public void run() {
          users check = new users(username, password);
          signIn(user, check)
        }
      }, delay, TimeUnit.MILLISECONDS);
    }
  } catch (InterruptedException e) {
    //The code to catch the exception takes the same amount of time to execute, on purpose
    ScheduledExecutorService executor = Executors.newScheduledThreadPool(2);
      executor.schedule(new Runnable(){
        public void run() {
          failedSignin(user)
        }
      }, delay, TimeUnit.MILLISECONDS);
  }
}

Non compliant code​

The app provides a different ftps when a query is successful than when the login has failed because of a delay in getting the data

public static void main(String[] args) {
  Scanner input = new Scanner(System.in);
  String username;
  String password;
  username = input.next();
  password = input.next();

  try {
    Thread.sleep(5000);
    if(username.equals(username) && password.equals(password)){
      ScheduledExecutorService executor = Executors.newScheduledThreadPool(2);
      executor.schedule(new Runnable(){
        public void run() {
          users check = new users(username, password);
          signIn(user, check)
        }
      }, delay, TimeUnit.MILLISECONDS);
    }
  } catch (InterruptedException e) {
    //Code to catch the exception that executes faster than the login code...
  }
}

Requirements​

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