Executive Summary

This vulnerability affects certain versions of Mattermost (10.11.x up to 10.11.18, 11.6.x up to 11.6.3, and 11.5.x up to 11.5.6) where markdown image rendering restrictions are not properly applied to AI bot tool result posts.

Because of this, an authenticated attacker can inject markdown image syntax into the content generated by AI bot tools. When a victim's client renders this content, it can cause data to be exfiltrated to a server controlled by the attacker.

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Impact Analysis

The vulnerability allows an authenticated attacker to exfiltrate data from a victim's client by injecting malicious markdown image syntax into AI bot tool result posts.

This could lead to unauthorized disclosure of sensitive information to an attacker-controlled server.

The CVSS score of 3.5 indicates a low severity impact, with limited confidentiality impact and no integrity or availability impact.

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Mitigation Strategies

To mitigate this vulnerability, you should update Mattermost to a version later than 10.11.18 for the 10.11.x branch, later than 11.6.3 for the 11.6.x branch, or later than 11.5.6 for the 11.5.x branch, where the markdown image rendering restrictions issue has been fixed.

Additionally, stay informed about security updates by subscribing to Mattermost's Security Bulletin and regularly checking their security updates page.

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