The 'Reprompt' attack is a novel vulnerability discovered in Microsoft Copilot, an AI-powered assistant integrated into Microsoft products. This attack circumvents Copilot's existing data leak protections by exploiting flaws in session management, allowing attackers to silently siphon data from active sessions. Notably, the exfiltration can continue even after the user has closed the Copilot chat interface, indicating that session termination processes do not fully revoke data access or stop background data flows. The attack likely leverages reprompting mechanisms or residual session tokens to maintain unauthorized access. Although specific technical details such as the exact exploitation vector or affected versions are not provided, the vulnerability underscores a critical gap in safeguarding AI assistant sessions against persistent data leakage. No known exploits have been reported in the wild, and no patches or CVEs have been issued yet. The severity is currently rated as low by the source, but the potential for confidential data exposure remains significant, especially in environments handling sensitive information. This vulnerability raises concerns about the robustness of AI assistant security models and the need for comprehensive session lifecycle management.

For European organizations, the 'Reprompt' attack poses a risk primarily to the confidentiality of sensitive data processed through Microsoft Copilot. Organizations relying on Copilot for document drafting, code generation, or data analysis could inadvertently expose proprietary or personal data if the attack is exploited. The silent nature of the exfiltration means that traditional monitoring might not detect the breach promptly, increasing the window of exposure. This could lead to data privacy violations under GDPR, reputational damage, and potential regulatory penalties. The attack does not appear to affect system integrity or availability directly but compromises trust in AI-assisted workflows. Sectors such as finance, healthcare, and government, which often use Microsoft enterprise tools extensively, are particularly vulnerable. The impact is amplified in environments where session management and endpoint security controls are weak or inconsistent.

To mitigate the 'Reprompt' attack, organizations should: 1) Monitor for unusual data flows from Copilot sessions, especially after chat closure, using advanced network and endpoint detection tools. 2) Enforce strict session termination policies ensuring that all session tokens and background processes are fully invalidated upon chat closure. 3) Apply the principle of least privilege to Copilot access, limiting data exposure to only necessary users and contexts. 4) Collaborate with Microsoft to obtain and deploy any patches or updates addressing this vulnerability as soon as they become available. 5) Conduct security reviews of AI assistant integrations, focusing on session lifecycle and data handling practices. 6) Educate users about the risks of sensitive data input into AI tools and encourage minimizing exposure of confidential information. 7) Implement data loss prevention (DLP) solutions tailored to monitor AI tool interactions. These steps go beyond generic advice by focusing on session management integrity and proactive monitoring specific to AI assistant environments.