Client Side Vulnerabilities / Cross Site Flashing

Web and API


Cross Site Flashing (CWE-959) is a vulnerability that allows attackers to inject malicious content into a vulnerable web or API application. It is a type of client-side vulnerability that occurs when a vulnerable application allows an attacker to inject malicious content into a web page or API call. The malicious content can then be displayed to users when they interact with the application. According to the CWE directory, this vulnerability is caused by "the failure to properly filter or validate user-controllable input". The OWASP Testing Guide defines Cross Site Flashing as "an attack that involves the injection of malicious content into an application that can be displayed to other users".


Cross Site Flashing has a high risk rating, as it can be used by attackers to gain access to sensitive information, execute malicious code, or compromise an application. The malicious content injected by the attacker can be used to steal user credentials, hijack sessions, redirect users to malicious websites, or provide access to sensitive data. Additionally, the malicious content can be used to execute malicious code on the user’s device.


The best way to mitigate the risk of Cross Site Flashing is to properly filter and validate user-controllable input, such as form fields and query strings. Additionally, it is important to ensure that the application is properly configured to reject malicious input. Furthermore, applications should use a secure HTTP header to prevent the injection of malicious content.


The following example demonstrates a Cross Site Flashing attack. The attacker injects malicious content into a vulnerable application. The malicious content is then displayed to the user when they interact with the application:

<script>alert('Cross Site Flashing Attack!');</script>

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