Stored XSS in K2 for Joomla via Unsanitized embedVideo Field

Mitigation Strategies

Immediate mitigation steps include restricting or reviewing the permissions of Joomla users who have K2 "create item" rights, especially those at the Author tier by default.

Implement input validation or sanitization on the embedVideo POST field to prevent raw <script> tags from being stored and rendered.

If possible, apply patches or updates from the K2 or JoomlaWorks developers that address this vulnerability.

As a temporary measure, disable or limit the embedVideo functionality for users who do not require it.

Monitor and audit articles submitted by users with create item rights for suspicious embedded scripts and remove any malicious content.

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Detection Guidance

This vulnerability involves a Joomla user with K2 "create item" rights submitting an article with a raw <script> tag in the embedVideo POST field, which is stored and rendered unescaped. Detection would involve inspecting POST requests to the K2 component for the presence of <script> tags in the embedVideo field.

You can monitor HTTP POST requests to the K2 article creation endpoint and look for suspicious payloads containing <script> tags in the embedVideo parameter.

Example commands to detect such attempts might include using network traffic inspection tools or web server logs with grep, such as:

• Using tcpdump or tshark to capture HTTP POST data and filter for embedVideo containing <script>:
• tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep 'embedVideo=.*<script>'
• Searching web server access logs for POST requests with embedVideo containing <script>:
• grep -i 'POST' /var/log/apache2/access.log | grep 'embedVideo=.*<script>'

Additionally, reviewing the database entries for articles created by users with create item rights to check for unescaped <script> tags in the embedVideo field can help detect exploitation.

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Compliance Impact

The vulnerability allows a Joomla user with K2 'create item' rights to submit an article containing a raw <script> tag in the embedVideo POST field, which is stored and rendered unescaped to visitors. This could lead to cross-site scripting (XSS) attacks, potentially exposing users to malicious scripts.

Such exposure could impact compliance with standards and regulations like GDPR and HIPAA, which require protection of user data and secure handling of web content to prevent unauthorized access or data breaches.

However, the provided information does not explicitly detail the direct impact on compliance with these regulations.

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Executive Summary

This vulnerability occurs in Joomla when using the K2 extension. A user with 'create item' rights (typically an Author tier user) can submit an article containing a raw <script> tag inside the 'embedVideo' POST field.

K2 stores this script tag verbatim and renders it unescaped on the article page, meaning that any visitor to that page will have the script executed in their browser.

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Impact Analysis

This vulnerability can lead to Cross-Site Scripting (XSS) attacks, where malicious scripts are executed in the browsers of visitors to the affected article pages.

• Attackers can steal session cookies or authentication tokens.
• It can be used to deface the website or inject malicious content.
• It may allow attackers to perform actions on behalf of users or redirect them to malicious sites.

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