Cross-Site Scripting in MyBB Thread Redirect Plugin

Executive Summary

CVE-2018-25116 is a cross-site scripting (XSS) vulnerability in the MyBB Thread Redirect Plugin version 0.2.1. It occurs because the plugin's custom text input field for thread redirects does not properly sanitize user input, allowing attackers to inject malicious SVG scripts. When other users view the affected thread, these scripts execute, enabling arbitrary script execution. [1, 2]

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Impact Analysis

This vulnerability can allow attackers to execute arbitrary scripts in the context of users viewing the affected forum threads. This can lead to theft of user credentials, session hijacking, defacement, or other malicious actions performed on behalf of the user without their consent. [1, 2]

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Detection Guidance

This vulnerability can be detected by checking for the presence of the MyBB Thread Redirect Plugin version 0.2.1 on your MyBB forum installation and testing the custom text input field for thread redirects for improper input sanitization. A practical detection method is to create or monitor threads that include suspicious SVG payloads such as `<svg/onload=alert('XSS')>` in the custom text input field and observe if the script executes when the thread is viewed. There are no specific network commands provided, but manual testing of the input field or automated scanning for XSS payloads in thread redirect messages can help detect the vulnerability. [2]

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Mitigation Strategies

Immediate mitigation steps include disabling or uninstalling the MyBB Thread Redirect Plugin version 0.2.1 until a patched version is available. Additionally, restrict permissions so that only trusted user groups can create redirecting threads with custom text. Avoid allowing untrusted users to input custom text in thread redirects. Applying input sanitization or escaping on the custom text input field to prevent script injection is also recommended. Monitoring and removing any threads containing malicious SVG scripts can help reduce risk. [1, 3]

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