Reflected

Reflected Cross-Site Scripting

Overview of the Vulnerability

Reflected Cross-Site Scripting (XSS) is a type of injection attack where malicious JavaScript code is injected into a website. When a user visits the affected web page, the JavaScript code executes and its input is reflected in the user’s browser. Reflected XSS can be found on this domain which allows an attacker to create a crafted URL. When opened by a user, this URL will execute arbitrary Javascript within that user’s browser in the context of the domain.

When an attacker can control code that is executed within a user’s browser, they are able to carry out any actions that the user is able to perform, including accessing any of the user's data and modifying information within the user’s permissions. This can result in modification, deletion, or theft of data, including accessing or deleting files, or stealing session cookies which an attacker could use to hijack a user’s session.

Business Impact

Reflected XSS could lead to data theft through the attacker’s ability to manipulate data through their access to the application, and their ability to interact with other users, including performing other malicious attacks, which would appear to originate from a legitimate user. These malicious actions could also result in reputational damage for the business through the impact to customers’ trust.

Steps to Reproduce

  1. Enable a HTTP interception proxy, such as Burp Suite or OWASP ZAP

  2. Use a browser to navigate to: {{URL}}

  3. Forward the following request to the endpoint:

{{request}}

  1. Observe the JavaScript payload being executed

Proof of Concept (PoC)

Below is a screenshot demonstrating the injected JavaScript executing at the vulnerable endpoint:

{{screenshot}}

This XSS vulnerability could be further abused by using the following JavaScript payload:

Here is a screenshot of the full exploit taking place:

{{screenshot}}

Guidance

Provide a step-by-step walkthrough with a screenshot on how you exploited the vulnerability. This will speed triage time and result in faster rewards.

Your submission must include evidence of the vulnerability and not be theoretical in nature.

Recommendation(s)

There is no single technique to stop XSS from occurring. However, implementing the right combination of defensive measures within the application will prevent and limit the impact of XSS. Some best practices include the following:

  • All user input fields should be sanitized based on what the field is likely to contain. For example, a date field (01/01/2001) should only contain a maximum of 10 characters consisting of numbers and forward slashes. Additionally, drop down or pick lists can be used for allowable inputs to ensure expected values are sent to the server.

  • Use appropriate HTTP response headers to ensure the browser correctly interprets responses. These should be customized specific to the application and its environment. For example:

For more information, please see Open Web Application Security Project (OWASP) guides located at:

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