Cross-site Scripting - CompTIA Security+ SY0-701 - 2.3
Cross-Site Scripting (XSS) Explained
Introduction to XSS
- Cross-site scripting, abbreviated as XSS, is a web security vulnerability that allows attackers to inject malicious scripts into trusted websites. This term was chosen to avoid confusion with CSS (Cascading Style Sheets) which shares the same abbreviation.
Understanding the Vulnerability
- XSS exploits vulnerabilities in browsers that allow information from one site to be shared with another, making it one of the most common vulnerabilities for web applications. The attack leverages the trust that browsers have in different websites.
- JavaScript is often used in these attacks due to its widespread use and default enablement in most browsers, making it an effective tool for attackers.
Mechanism of Attack
- An attacker can exploit a cross-site scripting vulnerability by sending a link containing a malicious script to a victim via email or text message. When clicked, this link directs the victim to a trusted website while executing the malicious script behind the scenes.
- The executed script can capture sensitive data such as cookies and session details without the victim's knowledge, effectively compromising their private information.
Types of XSS Attacks
Non-Persistent (Reflected) Attacks
- A non-persistent or reflected attack occurs when an attacker sends a link exploiting user input fields on third-party sites that allow script execution, such as search engines. The attacker’s code runs when users interact with these vulnerable fields, potentially exposing sensitive data like session IDs directly to the attacker.
Persistent (Stored) Attacks
- In persistent attacks, an attacker posts malicious JavaScript on social media platforms or other sites where it remains stored and executes whenever someone visits that page. This method allows attackers to target multiple users simultaneously as they view or share infected content across networks.
Example of Vulnerability Exploitation
- An example illustrates how an e-commerce site might lack proper validation on input fields like credit card numbers, allowing attackers to embed scripts within those fields. When victims submit their information along with embedded scripts, sensitive session data is sent back to the attacker instead of being displayed visibly on-screen for them to see.
Conclusion: Implications of XSS Attacks
Subaru Website Security Vulnerabilities
Token Management Issues
- The Subaru website provides a token upon login that never expires, which is not aligned with best security practices. Typically, tokens should have an expiration period to enhance security.
- The lack of expiration for the token allows users to perform any service request on their vehicle, creating significant security risks. An attacker could potentially add their email address to another user's account using the same token.
Cross-Site Scripting Vulnerability
- A cross-site scripting vulnerability was identified on the Subaru website, enabling attackers to send malicious links that could capture user tokens from victims.
- Once an attacker obtains a user's token, they gain indefinite access to manage any vehicle associated with that account due to the non-expiring nature of the token.
Resolution and Prevention Strategies
- Fortunately, a security researcher discovered these vulnerabilities and reported them to Subaru, leading to prompt resolution and removal of the issues.
- To protect against cross-site scripting attacks, users are advised not to click untrusted links in emails or messages. Instead, they should manually enter trusted domain names in their browser.