Cross site scripting (XSS) is a kind of security vulnerability that happens when a web application fails to properly validate and sanitize user input. Allowing attackers to inject and execute malicious scripts into web pages that other users are seeing. When a web application contains user-supplied data in its output without proper escaping or validation. This vulnerability happens.
In most cases, an attacker injects malicious JavaScript code onto a vulnerable website. When another person accesses the infected web page. Their browser executes the injected script unintentionally. Which can lead to a variety of harmful activities.
Stealing sensitive information (such as login passwords or personal data), changing website content, sending users to malicious websites. Or even seizing control of the victim’s account are examples of these behaviors.
There are three main types of cross-site scripting attacks
1. Stored (Persistent) XSS
Stored (or persistent) cross-site scripting (XSS) is a sort of XSS attack. In which the injected malicious script or code is permanently saved on the target server, generally in a database, and then served to users. When they access specified pages or content. This separates it from reflected XSS. In which the injected script is included in a request and reflected back to the victim’s browser.
In a stored XSS attack, the attacker discovers a weakness in a web application. That allows them to introduce malicious code into the program’s database. This vulnerability can be caused by insufficient input validation or sanitization of user-generated content before putting it in the database. Comment sections, user profiles, message boards, and other user-generated content areas are common entry points for the attacker to inject malicious code.
When a victim views a page or content that contains the stored malicious script. The malicious script is obtained from the server’s database and sent to the victim’s browser as part of the web page. The script is interpreted by the victim’s browser as valid code from a trusted website and executed inside the context of that page.
To prevent stored XSS attacks, web developers should include effective input validation and sanitization procedures. All user-generated content should be verified, and any special characters or script tags should be escaped or encoded. Before being stored in the database. Additionally, web application security testing, code reviews, and vulnerability scanning may help in identifying and correcting such flaws.
2. Reflected (Non-Persistent) XSS
Reflected (or non-persistent) cross-site scripting (XSS) is a kind of XSS attack. In which the injected malicious script or code is included in a request. Such as a URL parameter or a form submission, and then mirrored back to the victim’s browser in the response. Unlike stored XSS, the injected script is not permanently kept on the target server or in a database.
To prevent reflected XSS attacks, web developers should use correct input validation and output encoding techniques. They should check and sanitise any user-generated input before using it in the response to ensure that special characters and scripts are appropriately escaped or encoded.
Web users can protect themselves by being alert. When clicking on links or submitting forms, especially from untrusted sources. It is essential to pay attention to website URLs and avoid entering important data on dubious or unfamiliar sites. Updating online browsers and programmes, as well as employing browser extensions that block or warn about potentially harmful scripts, can give extra security against reflected XSS attacks.
3. DOM-based XSS
DOM-based XSS (cross-site scripting) is a kind of XSS attack in which a vulnerability occurs within a web page’s Document Object Model (DOM). It is triggered by dangerous modification of the DOM by client-side scripts, as opposed to stored or reflected XSS, which rely on flaws in server-side code.
The following is an example of a typical DOM-based XSS attack:
- The attacker detects a web page that has client-side scripts that process user input in an unsafe manner. This script can accept input from URL segments, query parameters, or any other user-controllable data.
- The attacker builds a malicious payload and manipulates user-controlled data to inject it into a vulnerable web page. An attacker, for example, could change a URL fragment to include script tags containing malicious code.
- When the victim visits the modified web page, the vulnerable client-side script executes and manipulates the DOM based on the injected payload. This may include accessing and changing page components, as well as the execution of inserted scripts.
- The modified DOM, including the injected script, is processed by the victim’s browser, resulting in the execution of malicious code within the context of the web page.
Due to their reliance on client-side code execution, DOM-based XSS attacks can be difficult to identify and prevent. As a result, limiting the risk of such attacks requires a combination of secure coding practises and user knowledge.
FAQ
Q: How does XSS operate?
A: XSS attacks primarily involve injecting malicious scripts into susceptible web pages, commonly in the form of HTML or JavaScript code. When other users visit these pages, their browsers execute the injected scripts. Which can result in a variety of outcomes. Such as stealing personal information, hijacking sessions, or defacing websites.
Q: What are the possible consequences of XSS attacks?
A: XSS attacks can have a variety of outcomes, including:
- Theft of sensitive information (such as login passwords or personal information).
- User impersonation or hijacking of sessions.
- Websites are being hacked.
- Malware or malicious content distribution to other users.
- Manipulation of website content or functionality without authorization.
Q: How can XSS vulnerabilities be avoided?
A: To avoid XSS vulnerabilities, developers should use the following security measures:
- Validation and sanitization of user input: Validate and sanitise every user input to ensure that special characters are correctly encoded or deleted.
- Output encoding: Encode user-generated content before displaying it in web pages to avoid script execution.
- CSP (Content Security Policy): Use CSP headers to prevent scripts from being executed from illegal sources.
- Take advantage of security frameworks and libraries: Use security frameworks and libraries with built-in protection against XSS attacks.
- Patching and security updates on a regular basis: Maintain the web application and its components’ security fixes to resolve known vulnerabilities.
Q: How can I test for cross-site scripting vulnerabilities?
A: XSS testing is attempting to inject scripts into input fields and analysing the application’s response. This can be done manually or with the help of automated tools.
These FAQs provide an overview of XSS and its consequences. It is essential to stay up to date on the newest security practises and guidelines for protecting web applications from XSS attacks.
Also Read:
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The 8 Best Free Web Application Penetration Testing Tools
