Reprompt Attack Enables Single-Click Data Theft from Microsoft Copilot

Researchers Uncover Reprompt Attack Targeting Microsoft Copilot

Cybersecurity researchers at Varonis have disclosed a novel attack vector, dubbed Reprompt, that enables threat actors to exfiltrate sensitive data from Microsoft Copilot with just a single click. The attack bypasses enterprise security controls entirely, posing a significant risk to organizations leveraging AI-driven chatbot assistants.

Technical Details of the Reprompt Attack

The Reprompt attack exploits a combination of legitimate Microsoft links and AI chatbot functionality to compromise victims. According to Varonis, the method requires only one click on an apparently benign Microsoft URL to trigger data exfiltration. While specific technical mechanics remain under embargo pending Microsoft’s remediation efforts, the attack appears to leverage:

• AI prompt manipulation to extract sensitive information from Copilot interactions
• Legitimate Microsoft domains to evade detection by security tools
• Single-click execution, reducing the need for complex social engineering

The attack does not rely on traditional malware or phishing techniques, making it particularly stealthy against conventional defenses.

Impact and Risks

The Reprompt attack introduces several critical risks for enterprises:

• Data Exfiltration: Threat actors can extract confidential corporate data, including emails, documents, and internal communications, without triggering alerts.
• Security Bypass: The attack circumvents existing security controls, including email filtering, endpoint protection, and AI-specific monitoring tools.
• Low Barrier to Entry: With only a single click required, the attack lowers the threshold for successful compromise, increasing the likelihood of widespread exploitation.

Microsoft Copilot, integrated into Microsoft 365, is widely adopted in enterprise environments, amplifying the potential impact of this vulnerability. Organizations relying on Copilot for productivity may face heightened exposure to data breaches.

Recommendations for Security Teams

While Microsoft has not yet released a patch, security professionals are advised to:

1. Monitor AI Interactions: Implement logging and anomaly detection for Copilot queries and responses to identify unusual data access patterns.
2. Restrict Sensitive Data Access: Limit Copilot’s permissions to access only non-sensitive or strictly necessary corporate data.
3. User Awareness Training: Educate employees on the risks of clicking links, even those appearing to originate from Microsoft, and emphasize vigilance in AI-assisted workflows.
4. Deploy Advanced Threat Detection: Utilize behavioral analysis and AI-driven security tools to detect anomalous exfiltration attempts.
5. Stay Updated: Follow Microsoft’s security advisories for patches or mitigations related to the Reprompt attack.

Varonis has indicated that further technical details will be released following Microsoft’s remediation efforts. Security teams are urged to treat this as an active threat and adjust defenses accordingly.