CVE-2026-24307 is a critical security vulnerability identified in Microsoft 365 Copilot, a productivity enhancement tool integrated into Microsoft 365 services. The vulnerability stems from improper validation of the specified type of input (CWE-1287), which allows an attacker to craft malicious inputs that bypass normal validation checks. This flaw can be exploited remotely over a network without requiring any privileges, although it does require user interaction, such as triggering the Copilot feature with crafted input. Successful exploitation results in unauthorized disclosure of sensitive information, impacting both confidentiality and integrity of data processed by the Copilot service. The vulnerability has a CVSS 3.1 base score of 9.3, indicating critical severity, with attack vector network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), user interaction required (UI:R), and scope changed (S:C). The impact includes high confidentiality and integrity loss but no impact on availability. Although no exploits are currently known in the wild, the vulnerability's nature and the widespread use of Microsoft 365 Copilot make it a significant risk. The vulnerability was published on January 22, 2026, and no patches have been linked yet, emphasizing the need for proactive mitigation. The improper input validation could allow attackers to exfiltrate sensitive corporate or personal data by manipulating the input types processed by Copilot, potentially leading to data breaches or further attacks leveraging disclosed information.

For European organizations, the impact of CVE-2026-24307 is substantial due to the widespread adoption of Microsoft 365 services across enterprises and public sector entities. The vulnerability can lead to unauthorized disclosure of sensitive corporate data, intellectual property, and personal information, which may result in regulatory penalties under GDPR and damage to organizational reputation. The integrity impact could allow attackers to manipulate data outputs or responses from Copilot, potentially influencing business decisions or automated workflows. Given the network attack vector and no privilege requirement, attackers can exploit this vulnerability remotely, increasing the risk of large-scale data leakage. The requirement for user interaction means phishing or social engineering could be used to trigger the exploit. The lack of current known exploits provides a window for mitigation, but the critical severity demands urgent attention. Organizations relying heavily on Microsoft 365 Copilot for automation and productivity enhancements are particularly vulnerable, and the potential for cross-tenant impact in multi-tenant cloud environments raises concerns about broader exposure.

1. Monitor Microsoft security advisories closely and apply patches or updates for Microsoft 365 Copilot immediately upon release. 2. Until patches are available, restrict access to Microsoft 365 Copilot features to trusted users and limit exposure to untrusted or external users. 3. Implement network-level monitoring and anomaly detection to identify unusual data exfiltration or suspicious Copilot-related traffic. 4. Educate users about the risks of interacting with unsolicited or unexpected Copilot prompts to reduce the likelihood of user interaction exploitation. 5. Employ strict input validation and sanitization policies on any custom integrations or scripts interacting with Microsoft 365 Copilot APIs. 6. Review and tighten access controls and permissions related to Microsoft 365 Copilot usage within the organization. 7. Conduct regular security assessments and penetration testing focused on Microsoft 365 services to identify potential exploitation paths. 8. Consider deploying data loss prevention (DLP) solutions to detect and block unauthorized data disclosures originating from Microsoft 365 environments.