Cross Site Script (XSS) Vulnerability

Cross-site Scripting (XSS) is a common attack vendor that injects attacks when an attacker performs malicious scripts (also commonly known as a malicious payload) into a legal and trusted website or web application. XSS is one of the common attacks that use a trusted web application to send any unauthentic or unencoded code, which is in the form of a browser side script, to a different end user.

By using XSS, the attacker can easily target a victim’s web page and also can exploit the vulnerability within the website or web application visited by the victim. The attacker can insert his own HTML code on the victim’s web page and can get access to other pages on the same domain and can read data like CSRF-Tokens or the set cookies. The web browser will still show the user’s code since it belongs to the website where it is inserted. Therefore, by using the vulnerable website the attacker can deliver a malicious script to the victim’s browser.

The XSS can easily get the benefit of within VBScript, ActiveX and Flash (now considered legal or even neglected), undoubtedly, the most widely abused is JavaScript as it is primary to most browsing experiences.

How Cross-site Scripting works

XSSThe malicious JavaScript runs in a victim browser and an attacker in order to run the JavaScript first find a way to inject a payload on the web page visited by the victim. Therefore, this helps the attacker to use some engineering tool on a web page that the victim visits. By using social engineering techniques the attacker further convinces a user to visit a vulnerable page that has an injected JavaScript payload.

When the vulnerable website includes user input in its pages, then only XSS attack can take place. The attacker in order to attack the web page, insert a string within the web page that will be used within the web page and represent it as code by the victim’s browser.

To display the most recent comment on a web page, following server-side pseudo-code is used.

print “<html>” print “<h1>Most recent comment</h1>” print database.latestComment print “</html>”

The above script helps in printing the latest comments from the comment database and presume that the comments published on HTML page only consists of text.

Also, the comments created on the web page are vulnerable to XSS because the attacker could easily submit any comment that may contain a malicious payload such as

<script>doSomethingEvil();</script>.

So, when any user visits the web page, he will get following HTML page.

<html> <h1>Most recent comment</h1> <script>doSomethingEvil();</script> </html>

Therefore, when the victim loads the web page in his browser the attacker can easily execute the malicious script without even letting the user know that he is being attacked by the attacker or cannot prevent such an attack.

Thus, we can say that an XSS vulnerability only exists if the malicious script (payload) injected by the attacker get eventually resolved (as HTML in this case) in the victim’s browser.

Is your website or web application vulnerable to Cross-site scripting?

internetIdentify that your website is vulnerable to XSS or not. One of the most widespread web application vulnerability on the internet is the XSS vulnerabilities. Luckily, there have been various ways to fix the vulnerability.

How to fix vulnerability in Cross Site Scripting?

Vulnerabilities in Cross Site Scripting is at a high-risk vulnerability and also have high frequency and high visibility. This condition is the most severe combination of security factors that exists and has become extremely important to know the problem and find it on your network. By finding a web security scanner you can easily fix these problems. They perform fully automated tests, run an automated vulnerability scan to identify the security issues on your website or web application.

Ways to Keep Cross-Site Scripting Out of Your Apps

Here are 3 ways to keep Cross-Site Scripting out of your Apps Let’s dive into some best-known practices that allow in preventing them in the first place.

  1. Escaping

One of the first methods you can try to prevent XSS vulnerabilities from appearing in your applications is by escaping user input. You can escape data from entering the application by ensuring it’s secure before executing it for the end user. When you escape the user input, the key characters received by a web page will be restricted from being performed in any malicious way.

  1. Validating Input

Anything that comes from an outside source of the system which you don’t have control is an untrusted data which include form data, query strings, cookies, other request headers, data from other systems. So, by validating input you can ensure whether the application rendering is correct or not and easily prevent malicious data from doing harm to the site, database, and users.

  1. Sanitizing

The third way to prevent the cross-site scripting attacks is to sanitize user input. The Sanitizing data process is a strong security, but this method should not be performed alone to fight XSS attacks. Sanitizing user input is particularly effective on sites that support HTML markup, and guarantee that the data received will not harm to your database. Sanitizing cleans all the data of possible harmful markup and change any unacceptable user input to an acceptable format.

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CVE-2018-0886 – CredSSP Encryption Oracle Remediation

You can also use all these above methods as by using layers of security, there is a great chance to prevent XSS attacks. Also, it’s important to remember that these methods above are prevention from most XSS attack vectors and they won’t cover everything.

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