Executive Summary

CVE-2026-27568 is a Stored Cross-Site Scripting (XSS) vulnerability in the WWBN AVideo platform prior to version 21.0. The platform allows Markdown in video comments and uses the Parsedown library (version 1.7.4) without enabling Safe Mode. This lack of safe mode means Markdown links are not properly sanitized, allowing malicious javascript: URIs to be rendered as clickable links.

An authenticated attacker with low privileges can post a malicious comment containing persistent JavaScript. When other users click on the malicious link, the attacker can execute harmful actions such as session hijacking, privilege escalation (including taking over admin accounts), and data exfiltration.

The vulnerability was fixed in version 21.0 by enabling Safe Mode in Parsedown and escaping markup to prevent XSS attacks.

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Impact Analysis

This vulnerability can have serious security impacts if exploited. An attacker can inject persistent malicious JavaScript into video comments that other users might click.

• Session hijacking: The attacker can steal user sessions to impersonate victims.
• Privilege escalation: The attacker can escalate their privileges, potentially taking over administrator accounts.
• Data exfiltration: Sensitive data can be stolen from users or the system.

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Compliance Impact

I don't know

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Detection Guidance

[{'type': 'paragraph', 'content': 'This vulnerability involves malicious Markdown comments containing javascript: URIs that are rendered as clickable links, allowing persistent XSS attacks. Detection involves identifying such unsafe Markdown comments in video comment sections.'}, {'type': 'paragraph', 'content': 'You can detect the vulnerability by searching for comments containing suspicious Markdown links with javascript: schemes in your AVideo database or logs.'}, {'type': 'list_item', 'content': "Run a database query to find comments containing 'javascript:' URIs, for example in MySQL: SELECT * FROM comments WHERE comment LIKE '%javascript:%';"}, {'type': 'list_item', 'content': 'Inspect web server logs or application logs for requests containing suspicious Markdown content or unusual URL schemes.'}, {'type': 'list_item', 'content': 'Check the version of Parsedown used and whether Safe Mode is enabled in the application code (Parsedown v1.7.4 without Safe Mode is vulnerable).'}] [2]

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Mitigation Strategies

[{'type': 'paragraph', 'content': 'To mitigate this vulnerability immediately, you should enable Safe Mode in the Parsedown library used by AVideo to prevent rendering of unsafe HTML and JavaScript in Markdown.'}, {'type': 'paragraph', 'content': "Additionally, validate and block unsafe URI schemes such as 'javascript:' before rendering Markdown content."}, {'type': 'paragraph', 'content': 'Upgrading to AVideo version 21.0 or later, which contains the official fix, is recommended as a permanent solution.'}, {'type': 'list_item', 'content': 'Enable Parsedown Safe Mode by calling $parsedown->setSafeMode(true) and $parsedown->setMarkupEscaped(true) in the markDownToHTML function.'}, {'type': 'list_item', 'content': 'Implement input validation to block or sanitize unsafe URI schemes in user-submitted Markdown comments.'}, {'type': 'list_item', 'content': 'Consider removing or moderating existing comments that contain malicious javascript: links.'}] [1, 2]

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