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Payload Xss Protection Strategies: A Developer’s Handbook

Payload Xss Protection Strategies: A Developer’s Handbook

Payload Xss Protection Strategies: A Developer’s Handbook – This blog will help developers understand XSS, its types, how to detect and prevent it. XSS stands for cross-site scripting, a type of vulnerability.

Remember when a vulnerability was discovered in Microsoft Exchange Server that could allow a reflected cross-site scripting (XSS) attack? This RXSS could lead to unauthorized access to email accounts, phishing attacks, and other activities that could change the state of the affected application. XSS attacks are particularly dangerous because they allow attackers to execute malicious code in a user’s browser, potentially leading to the theft of sensitive information or even hijacking an entire account. However, Microsoft has resolved the issue by releasing a patch that addresses the vulnerability. This highlights the importance of updating software and regularly checking for security vulnerabilities.

Table of Contents

Payload Xss Protection Strategies: A Developer’s Handbook

Payload Xss Protection Strategies: A Developer's Handbook

XSS stands for “cross-site scripting,” a type of security vulnerability that allows attackers to inject malicious scripts into a web page that other users can see.

Xss And Its Types In Web App Penetration Testing

What if a web application has XSS? When a user visits an application that has a cross-site scripting vulnerability, the attacker’s script is executed by the user’s browser. Unfortunately, this allows an attacker to obtain sensitive information such as login credentials, session tokens, or personal data. It can also enable other malicious actions, such as manipulating page content, redirecting the user to a malicious website, or infecting the user’s system with malware. The potential for danger is limitless!

XSS has several levels. Let’s dive deeper into XSS types in the next section.

In 2019, a security researcher discovered a reflected XSS vulnerability in Google Translator. This vulnerability allows attackers to inject malicious code into translated text, which can then be executed when other people see it. Look at this picture below!

Reflected XSS is a type of cross-site scripting vulnerability that occurs when an application repeats user input in a response without properly validating or encoding it. This attack typically involves the attacker creating a malicious link or form containing a script. When the victim clicks a link or submits a form, their browser executes the script.

Content Security Policy (csp) And Its Bypasses

Let’s say you have an API endpoint that gets a list of articles based on a search query. The server then returns a list of articles in a JSON response that includes the article title, author, and content. Here is an example of vulnerable code that repeats user input without proper coding or validation:

In this example, the $search_query variable is not sanitized or validated and is included directly in the JSON response to the user, making it vulnerable to reflected XSS attacks. So how does an attacker perform the XSS reflected here? An attacker could create a malicious URL that includes a script as a request parameter. See below:

The victim’s browser executes the script and displays an alert box with the message “XSS”. An attacker could use it to steal the victim’s session cookies, passwords, or other sensitive data or perform other malicious actions. Dangerous!

Payload Xss Protection Strategies: A Developer's Handbook

Don’t worry! you can prevent this by using input validation in your code. Here’s how you can sanitize and validate all user input and encode any special characters before including them in the response.

Html Tags Converting Into Entity Characters In Xss

In this improved code, the htmlspecialchars function cleverly encodes any special characters entered by the user, such as , before including them in the JSON response. This input validation method effectively prevents the browser from misinterpreting the input as HTML or JavaScript code and instead displays it as plain text. Read on as I will discuss additional input validation methods in the blog.

In 2018, a security researcher discovered a stored cross-site scripting (XSS) vulnerability in Snapchat that allowed attackers to inject malicious code into business.snapchat.com. The vulnerability could allow an attacker to steal user credentials or perform other malicious actions.

Stored XSS, also known as persistent XSS, is a cross-site scripting attack in which malicious code is permanently stored in the database or server of the target application. Unlike reflected XSS, where malicious code is injected in response to a user request, stored XSS attacks can affect all users who access the affected page or resource. Stored XSS attacks occur when an attacker can send malicious data to a website, for example through a form or comment field, which is then stored and displayed to other users.

Let’s say you have an API endpoint that allows users to leave comments on an article. The server then stores the comments in the database and returns them in a JSON response, including the comment text and author. Here is an example of vulnerable code that stores user input without proper encoding or validation:

What Is Cross Site Scripting (xss) ? Impact, Remediation And Prevention

The $comment_text and $author variables are not cleared or checked in this example. They are included directly in the JSON response to the user, making it vulnerable to stored XSS attacks. An attacker could create a malicious comment that includes a script similar to the following:

The payload is an HTML img element with a src attribute set to x, which is not a valid image source. When the browser tries to load an image, an onerror event is raised because the image could not be loaded, and the JavaScript code inside the onerror attribute is executed.

In this case, the JavaScript code sets the src attribute of the img element to a URL that includes the victim’s cookies as a parameter. The document.cookie property is a string containing all the cookies associated with the current document, including the session cookie that identifies the user to the web application.

Payload Xss Protection Strategies: A Developer's Handbook

The URL in the payload points to an attacker-controlled web server (http://192.168.0.1:8888/), and cookies are included as a query string parameter (?cookies=).

Solving Dom Xss Puzzles

When a payload is injected into a vulnerable web page and the victim visits that page, their browser sends a request to the attacker’s server, including the session cookie as a parameter. The attacker can then use this cookie to impersonate the victim and perform actions on their behalf in the web application. Purchasing an account!

Don’t worry! you can prevent this by using input validation in your code. Here’s how you can sanitize and validate all user input and encode any special characters before storing it in the database.

In this case, we clear the $_POST[‘comment’] and $_POST[‘author’] variables using the htmlspecialchars function with the ENT_QUOTES and UTF-8 parameters to avoid any special characters being interpreted as code from the browser.

In 2022, a security researcher discovered a DOM-based cross-site scripting (XSS) vulnerability in the advertising platform TikTokads.tiktok.com. The vulnerability allowed an attacker to inject malicious code into the platform’s landing page and execute it in the user’s browser. This could potentially allow an attacker to steal user data or perform other malicious actions.

Understanding And Preventing Cross Site Scripting Vulnerabilities (xss)

DOM-based cross-site scripting (DOM XSS) is a type of cross-site scripting vulnerability that occurs in the Document Object Model (DOM), which is the browser’s representation of web page data. In a DOM-based XSS attack, the malicious payload is executed by insecurely modifying the DOM environment, rather than through traditional injection into the HTML source code or reflection in the server response.

The payload in a DOM-based XSS attack is often included in a URL or as part of client code and is typically executed when the victim interacts with the page in a certain way. For example, the payload may be activated when the victim clicks on a link, submits a form, or enters text into an input field.

This example asks the user to enter their name into an input field and click a button to submit the form. When the user clicks the button, it executes a JavaScript function called greet(). This function takes the value of the name input field and uses it to create a personalized welcome message that is displayed on the page.

Payload Xss Protection Strategies: A Developer's Handbook

However, there is a potential vulnerability in this code. If an attacker can manipulate the value of the name input field to include a script tag, they can inject malicious code into the page and execute it in the victim’s browser. For example, an attacker could enter the following:

Cybersecurity For Startups

In this example, the attacker injects a script tag into the page, which displays an alert box with the text “XSS!” show.

Here the developer has updated the Greeting() function to include input validation and output encoding in this example. The input validation step removes script tags from the name input field, preventing embedded scripts from executing. The encoding step of the export uses the encodeURIComponent() function to encode the value of the name variable, preventing special characters from being interpreted as executable code.

It is important to remember that the attack scenarios and code snippets presented above are simplified illustrations to help developers understand how to prevent XSS vulnerabilities. In real-world scenarios, the verification/prevention process may be more complex.

Our clients love us for our proactive approach and world-class API security testing models. Try the test library for yourself in your own test garden. Play with the default text or add your own

Why Injection Still Matters, Xss Attacks

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    1. Payload Xss Protection Strategies: A Developer's HandbookXSS stands for “cross-site scripting,” a type of security vulnerability that allows attackers to inject malicious scripts into a web page that other users can see.Xss And Its Types In Web App Penetration TestingWhat if a web application has XSS? When a user visits an application that has a cross-site scripting vulnerability, the attacker's script is executed by the user's browser. Unfortunately, this allows an attacker to obtain sensitive information such as login credentials, session tokens, or personal data. It can also enable other malicious actions, such as manipulating page content, redirecting the user to a malicious website, or infecting the user's system with malware. The potential for danger is limitless!XSS has several levels. Let's dive deeper into XSS types in the next section.In 2019, a security researcher discovered a reflected XSS vulnerability in Google Translator. This vulnerability allows attackers to inject malicious code into translated text, which can then be executed when other people see it. Look at this picture below!Reflected XSS is a type of cross-site scripting vulnerability that occurs when an application repeats user input in a response without properly validating or encoding it. This attack typically involves the attacker creating a malicious link or form containing a script. When the victim clicks a link or submits a form, their browser executes the script.Content Security Policy (csp) And Its BypassesLet's say you have an API endpoint that gets a list of articles based on a search query. The server then returns a list of articles in a JSON response that includes the article title, author, and content. Here is an example of vulnerable code that repeats user input without proper coding or validation:In this example, the $search_query variable is not sanitized or validated and is included directly in the JSON response to the user, making it vulnerable to reflected XSS attacks. So how does an attacker perform the XSS reflected here? An attacker could create a malicious URL that includes a script as a request parameter. See below:The victim's browser executes the script and displays an alert box with the message "XSS". An attacker could use it to steal the victim's session cookies, passwords, or other sensitive data or perform other malicious actions. Dangerous!Don't worry! you can prevent this by using input validation in your code. Here's how you can sanitize and validate all user input and encode any special characters before including them in the response.Html Tags Converting Into Entity Characters In XssIn this improved code, the htmlspecialchars function cleverly encodes any special characters entered by the user, such as , before including them in the JSON response. This input validation method effectively prevents the browser from misinterpreting the input as HTML or JavaScript code and instead displays it as plain text. Read on as I will discuss additional input validation methods in the blog.In 2018, a security researcher discovered a stored cross-site scripting (XSS) vulnerability in Snapchat that allowed attackers to inject malicious code into business.snapchat.com. The vulnerability could allow an attacker to steal user credentials or perform other malicious actions.Stored XSS, also known as persistent XSS, is a cross-site scripting attack in which malicious code is permanently stored in the database or server of the target application. Unlike reflected XSS, where malicious code is injected in response to a user request, stored XSS attacks can affect all users who access the affected page or resource. Stored XSS attacks occur when an attacker can send malicious data to a website, for example through a form or comment field, which is then stored and displayed to other users.Let's say you have an API endpoint that allows users to leave comments on an article. The server then stores the comments in the database and returns them in a JSON response, including the comment text and author. Here is an example of vulnerable code that stores user input without proper encoding or validation:What Is Cross Site Scripting (xss) ? Impact, Remediation And PreventionThe $comment_text and $author variables are not cleared or checked in this example. They are included directly in the JSON response to the user, making it vulnerable to stored XSS attacks. An attacker could create a malicious comment that includes a script similar to the following:The payload is an HTML img element with a src attribute set to x, which is not a valid image source. When the browser tries to load an image, an onerror event is raised because the image could not be loaded, and the JavaScript code inside the onerror attribute is executed.In this case, the JavaScript code sets the src attribute of the img element to a URL that includes the victim's cookies as a parameter. The document.cookie property is a string containing all the cookies associated with the current document, including the session cookie that identifies the user to the web application.The URL in the payload points to an attacker-controlled web server (http://192.168.0.1:8888/), and cookies are included as a query string parameter (?cookies=).Solving Dom Xss PuzzlesWhen a payload is injected into a vulnerable web page and the victim visits that page, their browser sends a request to the attacker's server, including the session cookie as a parameter. The attacker can then use this cookie to impersonate the victim and perform actions on their behalf in the web application. Purchasing an account!Don't worry! you can prevent this by using input validation in your code. Here's how you can sanitize and validate all user input and encode any special characters before storing it in the database.In this case, we clear the $_POST['comment'] and $_POST['author'] variables using the htmlspecialchars function with the ENT_QUOTES and UTF-8 parameters to avoid any special characters being interpreted as code from the browser.In 2022, a security researcher discovered a DOM-based cross-site scripting (XSS) vulnerability in the advertising platform TikTokads.tiktok.com. The vulnerability allowed an attacker to inject malicious code into the platform's landing page and execute it in the user's browser. This could potentially allow an attacker to steal user data or perform other malicious actions.Understanding And Preventing Cross Site Scripting Vulnerabilities (xss)DOM-based cross-site scripting (DOM XSS) is a type of cross-site scripting vulnerability that occurs in the Document Object Model (DOM), which is the browser's representation of web page data. In a DOM-based XSS attack, the malicious payload is executed by insecurely modifying the DOM environment, rather than through traditional injection into the HTML source code or reflection in the server response.The payload in a DOM-based XSS attack is often included in a URL or as part of client code and is typically executed when the victim interacts with the page in a certain way. For example, the payload may be activated when the victim clicks on a link, submits a form, or enters text into an input field.This example asks the user to enter their name into an input field and click a button to submit the form. When the user clicks the button, it executes a JavaScript function called greet(). This function takes the value of the name input field and uses it to create a personalized welcome message that is displayed on the page.However, there is a potential vulnerability in this code. If an attacker can manipulate the value of the name input field to include a script tag, they can inject malicious code into the page and execute it in the victim's browser. For example, an attacker could enter the following:Cybersecurity For StartupsIn this example, the attacker injects a script tag into the page, which displays an alert box with the text "XSS!" show.Here the developer has updated the Greeting() function to include input validation and output encoding in this example. The input validation step removes script tags from the name input field, preventing embedded scripts from executing. The encoding step of the export uses the encodeURIComponent() function to encode the value of the name variable, preventing special characters from being interpreted as executable code.It is important to remember that the attack scenarios and code snippets presented above are simplified illustrations to help developers understand how to prevent XSS vulnerabilities. In real-world scenarios, the verification/prevention process may be more complex.Our clients love us for our proactive approach and world-class API security testing models. Try the test library for yourself in your own test garden. Play with the default text or add your ownWhy Injection Still Matters, Xss Attacks
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