The reported security threat concerns Microsoft 365 Copilot, an AI-powered assistant integrated into Microsoft 365 productivity tools. The vulnerability involves the misuse of Mermaid diagrams, a popular text-based diagramming syntax supported within some Microsoft 365 components. Attackers can craft malicious Mermaid diagrams that exploit the rendering or processing logic within Copilot to exfiltrate arbitrary data from the victim's environment. This exfiltration occurs because the diagrams can be manipulated to include external references or encode sensitive information in a way that bypasses normal security controls. The issue was disclosed via a Reddit post in the netsec community and further detailed on a security blog by Adam Logue. Although the vulnerability is rated medium severity by the source, the lack of authentication or user interaction requirements and the potential for unauthorized data leakage elevate its risk. No official patches or CVEs have been published yet, and no active exploits are known in the wild. The threat leverages the integration of AI and diagram rendering, highlighting a novel attack vector in productivity suites. Organizations relying on Microsoft 365 Copilot should be aware of this vector, as it could lead to significant data confidentiality breaches if exploited.

For European organizations, the impact of this vulnerability could be substantial, particularly for those handling sensitive personal data under GDPR or critical business information. Unauthorized data exfiltration could lead to breaches of confidentiality, regulatory fines, reputational damage, and loss of customer trust. Sectors such as finance, healthcare, government, and legal services, which heavily use Microsoft 365 tools and rely on Copilot for productivity, are at heightened risk. The vulnerability could be exploited remotely without user interaction, increasing the attack surface. Data leakage could include intellectual property, personal identifiable information (PII), or internal communications. The lack of known exploits currently limits immediate risk, but the potential for future exploitation remains significant. European organizations with extensive cloud adoption and remote workforces are particularly vulnerable due to increased reliance on Microsoft 365 services.

Until Microsoft releases an official patch, organizations should implement strict controls on the use of Mermaid diagrams within Microsoft 365 environments. This includes disabling or restricting the rendering of Mermaid diagrams in Copilot-enabled applications where possible. Administrators should monitor network traffic for unusual outbound connections that could indicate data exfiltration attempts. Employ data loss prevention (DLP) policies tailored to detect and block suspicious diagram content or external references. Educate users about the risks of opening or sharing untrusted Mermaid diagrams. Regularly review and update access controls and audit logs related to Microsoft 365 Copilot usage. Once Microsoft issues a patch or update, prioritize its deployment across all affected systems. Additionally, consider isolating sensitive workloads or data from environments where Copilot and diagram rendering features are enabled to reduce exposure.