XSS (Cross-Site Scripting): Mechanisms, Damages, and Countermeasures
Cyberattacks are becoming increasingly diverse, with different attack methods resulting in different types of damage and requiring different countermeasures. Since companies and organizations are often targeted, it’s essential to understand the various cyberattack techniques and implement appropriate countermeasures at all times.
Among the many cyberattack methods, XSS (Cross-Site Scripting) is one of the most prevalent. This document provides a thorough explanation of XSS, from its overview and mechanism to examples of XSS attack damage and countermeasures. If you want to prevent cyberattacks or minimize potential damage, please refer to this guide.
Table of Contents
- XSS Definition
- XSS Mechanism
- Types of XSS
- Difference from SQL Injection
- Examples of XSS Attack Damage
- Information Leakage
- Session Hijacking
- Website Defacement
- Four Countermeasures Against XSS Attacks
- Sanitization (Escaping)
- Validation
- WAF Installation
- Allow Only Specific URLs
- Summary
1. What is XSS?
XSS (Cross-Site Scripting) is a cyberattack that exploits vulnerabilities in websites and web applications that dynamically generate pages based on user input to embed malicious scripts.
It’s named after the practice of redirecting users visiting a target site to another malicious website. It’s also called a “Cross-Site Scripting Attack.”
1-1. XSS Mechanism
XSS attackers primarily target sites that generate dynamic web pages, such as bulletin board sites and e-commerce sites. The attack mechanism and specific flow are as follows:
| (1) | The attacker enters a character code containing a link with a malicious script into the input form on the website. |
|---|---|
| (2) | A site visitor browses or uses the web site containing the trap. |
| (3) | The site visitor clicks on the link set up by the attacker. |
| (4) | The visitor is redirected to a website that serves as an entry point for malware infection, and the attack script is executed. |
The redirected website tends to have a design very similar to the original website. Therefore, many people may not realize that it is an attack website and enter important information such as personal information into the input form. As a result, simply browsing a website can lead to malware infection of devices or the theft of personal information.
1-2. Types of XSS
There are three main types of XSS attacks: “Reflected XSS,” “Stored XSS,” and “DOM Based XSS.”
| Reflected XSS | This XSS attack involves embedding a link containing a malicious script in a fake website or email, causing the user to request a vulnerable website, and then executing the attack script on the responded web page. It is also called “Reflective XSS.” |
|---|---|
| Stored XSS | This XSS attack involves directly storing a malicious script inside a website or application and executing the script each time a user views it. It is also called “Stored XSS.” |
| DOM Based XSS | This XSS attack involves exploiting JavaScript vulnerabilities to execute attack scripts against users who dynamically manipulate a website. |
1-3. Difference from SQL Injection
SQL Injection is an attack technique similar to XSS.
Both XSS and SQL injection are cyberattacks that exploit vulnerabilities in websites and web applications, and e-commerce sites are the primary targets.
However, XSS is fundamentally an attack that manipulates JavaScript and aims to steal and misuse personal information or conduct phishing scams. On the other hand, SQL injection is an attack that manipulates the database and aims to modify, delete, or steal data.
Thus, while XSS and SQL injection are similar techniques, it’s important to remember that their specific mechanisms and objectives differ.
2. Examples of XSS Attack Damage
XSS attacks can lead to various types of damage. To implement proper countermeasures, it’s essential to understand the specific types of damage that can occur due to XSS attacks.
Typical examples of damage caused by XSS attacks include “information leakage,” “session hijacking,” and “website defacement.” The following sections describe each type of damage in detail.
2-1. Information Leakage
One of the main examples of damage caused by XSS attacks is information leakage. If a user enters and submits personal information without knowing they are on a trap site, that important information will be extracted by the attacker.
E-commerce sites often require users to enter important information such as credit card details. If this information is stolen, it can lead to damages such as the fraudulent use of credit card information to purchase expensive products. In the worst case, it can be sold as an information list on dark web sites, potentially leading to further damage such as becoming a target for targeted attacks.
2-2. Session Hijacking
Session hijacking is an attack in which a session in network communication is illegally hijacked. This is a method of impersonating a legitimate user using individual session IDs or cookies.
If a session hijacking attack occurs, the attacker, impersonating a legitimate user or client, can infiltrate the server and steal confidential information or leak/modify registration information. In the case of e-commerce sites, this can lead to damages such as the fraudulent use of user credit card information.
2-3. Website Defacement
If an attacker who has launched an XSS attack infiltrates a server within the network, the website may be defaced. The content of the defacement can vary widely, from simple defacements that drastically change the design of the website for mischievous purposes to defacements aimed at spreading damage, such as infecting viewers with viruses.
Information leakage, session hijacking, and website defacement have all been reported as actual cases of damage in various companies.
3. Four Countermeasures Against XSS Attacks
XSS can cause various types of damage, including website defacement and information theft. For companies, this can significantly damage customer trust and brand reputation, so thorough attack countermeasures are essential.
When implementing XSS countermeasures, the key is to prevent vulnerabilities from being exploited, in other words, to minimize vulnerabilities as much as possible. Finally, here are four effective methods for countering XSS attacks.
3-1. Sanitization (Escaping)
Sanitization (escaping) is a processing method that replaces characters with special meanings such as delimiters and tags in HTML with character strings that have no special meaning, thereby disabling XSS attacks.
For example, if strings such as “<” and “>” which are recognized by the browser as part of a tag, are replaced with “<” or “>”, they will be displayed as simple strings rather than HTML. This prevents the script from behaving unintentionally.
3-2. Validation
Validation processing is a processing method that applies validation, so-called input value restrictions, to the input form system operated by the user.
For example, the password input field may be restricted to “alphanumeric characters of 7 or more characters including full-width characters” and the phone number input field may be restricted to “numbers only.” By doing so, unexpected values are not entered. As a result, it leads to preventing XSS attacks.
3-3. WAF Installation
WAF stands for “Web Application Firewall,” which is a type of security measure that specializes in attacks that exploit vulnerabilities in web applications.
By installing a WAF, network communication can be constantly monitored. Communication that is determined to be an attack can be blocked, preventing XSS attacks. Since it is difficult to constantly grasp and quickly correct all vulnerabilities, it can be said that it is a solution that should be introduced to prevent XSS attacks as much as possible.
In addition, there are three types of WAF products: “cloud-based WAF,” “host-based WAF,” and “gateway-based WAF.” Since the functions differ depending on the product, it is important to choose a product that suits your company.
3-4. Allow Only Specific URLs
URLs typically start with “http://” or “https://”, but some URLs start with “javascript:”. In cases where the URL entered by the user is dynamically generated in a way that depends on external input, there is a possibility that a malicious script will be executed when a string starting with “javascript:” is specified.
To prevent damage from such causes, it is recommended to allow only strings starting with “http://” or “https://” for the destination URL.
Summary
XSS is an attack technique that embeds malicious scripts by exploiting vulnerabilities in websites and web applications that dynamically generate pages according to user input information, and is characterized by the large number of damage cases.
If you are subjected to an XSS attack, there is a possibility that all kinds of damage may occur, such as information leakage, session hijacking, and website defacement, so always take measures such as sanitization processing and validation processing.
If you have any questions, please contact globalsupport@jiran.com.
