Executive Summary

CVE-2026-40571 is a vulnerability in NamelessMC versions prior to 2.2.5, a website software for Minecraft servers. The issue lies in the file core/classes/Misc/ProfilePostReactionContext.php, where the software only verifies that a wall post exists but does not enforce visibility restrictions for private or blocked profiles.

This flaw allows authenticated users with low privileges to add reactions to profile posts that are supposed to be private or blocked, bypassing intended access controls.

An attacker can exploit this by sending a specially crafted POST request to the reactions endpoint with the target post's ID, successfully adding a reaction even without proper authorization.

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Impact Analysis

This vulnerability can impact you by allowing unauthorized users to interact with private or blocked profile posts, potentially exposing private user interactions or preferences.

It undermines the privacy controls of the platform, as low-privileged users can react to content they should not have access to, which may lead to privacy violations or unwanted user engagement.

Although it does not allow direct data access or modification beyond reactions, it can still lead to information leakage about private posts and user activity.

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Detection Guidance

This vulnerability can be detected by monitoring for unauthorized POST requests to the reactions endpoint of NamelessMC prior to version 2.2.5. Specifically, look for POST requests where low-privileged authenticated users add reactions to profile posts that should be private or blocked.

A possible detection method is to analyze web server logs or use network monitoring tools to identify suspicious POST requests targeting the reactions endpoint with profile post IDs that belong to private or blocked profiles.

Example command to search web server logs for such POST requests (assuming Apache logs):

• grep 'POST /reactions' /var/log/apache2/access.log | grep -i 'profilepostid='

Further investigation should verify if the user performing the action has the appropriate permissions or if the reaction was added to a private or blocked profile post.

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Mitigation Strategies

The immediate mitigation step is to upgrade NamelessMC to version 2.2.5 or later, which contains the patch that enforces proper authorization checks on profile post reactions.

Until the upgrade can be applied, consider restricting access to the reactions endpoint to trusted users only or implementing additional access controls at the web server or application firewall level to block unauthorized reaction attempts.

Additionally, monitor logs for suspicious activity related to reaction additions on private or blocked profiles to detect potential exploitation.

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Compliance Impact

The vulnerability allows authenticated low-privileged users to add reactions to private or blocking profile posts without proper authorization, potentially exposing private user interactions.

This unauthorized access to private profile content could lead to violations of privacy requirements found in standards such as GDPR or HIPAA, which mandate strict controls over personal and sensitive information.

However, the provided information does not explicitly discuss compliance impacts or regulatory consequences.

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