What Is the Full Form of XSS?
Cross-Site Scripting (Also Known as XSS) Is a Web Security Vulnerability That Allows an Attacker to Compromise Users' Interactions with a Vulnerable Application.
How does XSS work?
Cross-site scripting (commonly known as XSS) is a web security flaw that enables an attacker to compromise the user interactions of a susceptible application. It allows an attacker to avoid the same-origin Policy, which is intended to separate different websites.
Cross-site scripting exploits a website's vulnerability to return harmful JavaScript to users. When the malicious code executes within a victim's browser, the attacker can compromise the victim's interaction with the application.
What are the different cross-site scripting (XSS) attacks?
XSS attacks are categorized into three categories. These are the following:
Reflected XSS is a type of XSS in which the malicious script originates from the current HTTP request. Stored XSS The dangerous script is stored in XSS and comes from the website's database. DOM-based XSS is a vulnerability in client-side code; rather than server-side code in XSS.
A simple example of a mirrored XSS vulnerability is as follows:
<p>Status: All is well.</p>
Because the application does not do any more data processing, an attacker can easily design an attack like this:
<p>Status: <script>/* Bad stuff here... */</script></p>
When a user hits the URL created by the attacker, the attacker's script runs in the user's browser during that user's session with the application. The script can then perform any operation and obtain any data the user has access to.
Reflected cross-site scripting
Cross-site scripting cheat sheet
Stored cross-site scripting
When an application obtains data from an untrusted source and includes that data in an unsafe fashion within its subsequent HTTP answers, this is known as stored XSS (also known as persistent or second-order XSS).
For example, comments on a blog post, user aliases in a chat room, or contact information on a client order may be submitted to the program via HTTP requests. In other circumstances, the data may come from untrustworthy sources, such as a webmail application that displays SMTP messages. This marketing application shows social media posts, or a network monitoring application that displays packet data from network traffic.
A simple example of a cached XSS vulnerability is shown below. Users can contribute messages to a message board application, which are then displayed to other users:
<p>Hello, this is my message!</p>
Because the application doesn't do anything else with the data, an attacker can easily send a message that targets other users:
<p><script>/* Bad stuff here... */</script></p>
DOM-based cross-site scripting
When an application has client-side JavaScript that processes data from an untrusted source in an unsafe way, usually by publishing the data back to the DOM, DOM-based XSS (also known as DOM XSS) occurs.
An application in the following example utilizes JavaScript to read the value from an input field and publish that value to an HTML element:
var search = document.getElementById('search').value;
var results = document.getElementById('results');
results.innerHTML = 'You searched for: ' + search;
If the attacker has control over the input field's value, they can easily create a negative value that executes their own script:
You searched for: <img src=1 onerror='/* Bad stuff here... */'>
In most cases, the input field is filled with data from the HTTP request, such as a URL query string parameter, allowing the attacker to launch an attack using a malicious URL, similar to reflected XSS. When all users are anonymous and all information is public, the impact is frequently minor in a brochureware application. The effect on an application that stores sensitive data, such as banking transactions, emails, or medical records, is frequently significant. The impact will usually be profound if the affected user has elevated rights within the application, allowing the attacker to gain complete control of the vulnerable application and compromise all users and their data.
How can XSS "cross-site scripting" be prevented?
Cross-site scripting vulnerabilities typically enable an attacker to impersonate a victim user, conduct whatever actions the user is capable of performing, and access any of the user's data. If the victim user has privileged application access, BMP: the attacker may acquire complete access to the application's functionality and data if this setting is enabled. Depending on the complexity of the application and how it manages user-controllable data, preventing cross-site scripting may be straightforward in some circumstances but significantly more difficult in others.
Encode data on output: Encode the output at the point where user-controllable data is output in HTTP responses to prevent it from being perceived as dynamic content. Depending on the output context, this may need HTML, URL, JavaScript, and CSS encoding.
Utilize the proper response headers: To avoid cross-site scripting (XSS) in HTTP answers that are not meant to contain HTML or JavaScript, you can use the Content-Type and X-Content-Type-Options headers to ensure that browsers read the responses as you intend.
Policy: Regarding the security of content as a last line of protection, you can employ Content Security Policy (CSP) to mitigate the impact of any remaining XSS vulnerabilities.
Cross-site scripting: Frequently Asked Questions
What are the most prevalent XSS flaws? XSS vulnerabilities are ubiquitous, and XSS is likely the most common web security flaw.
How often are cross-site scripting (XSS) attacks? Although reliable statistics on real-world XSS assaults are challenging, it is likely exploited less frequently than other vulnerabilities.
What's the difference between Cross-Site Request Forgery (XSS) and Cross-Site Request Forgery (CSRF)? XSS includes encouraging a victim user to undertake actions they did not mean to do. In contrast, CSRF involves inciting a victim user to conduct activities they did not plan to do.
What's the difference between SQL injection and XSS? SQL injection is a server-side vulnerability that targets the application's database, whereas XSS is a client-side vulnerability that targets other application users.
In PHP, how can I avoid XSS? Use an allowlist of acceptable characters and type hints or type casting to filter your inputs. For HTML contexts, use HTML entities and ENT QUOTES; for JavaScript situations, use JavaScript Unicode escapes.
In Java, how can I avoid XSS? Utilize a library like Google Guava to HTML-encode your output for HTML contexts. Use JavaScript Unicode escapes for JavaScript contexts, and filter your inputs with an allowlist of acceptable characters.
References:
> FORMFULL - "Xss"
> PORTSWIGGER - "Cross site scripting"
> SECURITY
