CVE-2026-24307 is a critical security vulnerability identified in Microsoft 365 Copilot, a widely used AI-powered productivity tool integrated into the Microsoft 365 suite. The vulnerability stems from improper validation of the specified type of input (CWE-1287), which means the software fails to correctly verify or sanitize the type of data it processes. This flaw can be exploited by an unauthorized attacker remotely over the network without requiring any privileges, although some user interaction is necessary. Exploitation leads to unauthorized disclosure of sensitive information, compromising confidentiality and integrity of data handled by the affected system. The CVSS v3.1 score of 9.3 reflects the critical nature of this vulnerability, with an attack vector of network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), and user interaction required (UI:R). The scope is changed (S:C), indicating that exploitation affects resources beyond the initially vulnerable component. The vulnerability does not impact availability (A:N) but has a high impact on confidentiality (C:H) and integrity (I:H). No patches or known exploits have been reported at the time of publication, but the vulnerability is publicly disclosed and should be treated as urgent. The improper input validation likely allows crafted inputs to bypass security checks, leading to unintended data exposure over the network, potentially leaking sensitive organizational or user information processed by Microsoft 365 Copilot.

For European organizations, the impact of CVE-2026-24307 is significant due to the widespread adoption of Microsoft 365 services across enterprises, government agencies, and critical infrastructure sectors. Unauthorized information disclosure can lead to data breaches involving sensitive corporate data, intellectual property, or personal data protected under GDPR, resulting in regulatory penalties and reputational damage. The integrity impact means that attackers could manipulate data or outputs generated by Copilot, potentially causing erroneous business decisions or operational disruptions. Since the vulnerability requires no privileges and can be exploited remotely, it increases the attack surface considerably. Organizations relying heavily on Microsoft 365 Copilot for productivity and collaboration are particularly vulnerable, as attackers could leverage this flaw to exfiltrate confidential information without detection. The lack of current patches means organizations must implement interim mitigations to reduce risk. The critical severity and network-based exploitation vector make this vulnerability a high priority for European cybersecurity teams.

1. Monitor official Microsoft security advisories closely and apply patches or updates for Microsoft 365 Copilot immediately upon release. 2. Implement network-level monitoring and anomaly detection to identify unusual outbound data flows that may indicate exploitation attempts. 3. Restrict or segment network access to Microsoft 365 Copilot services where feasible, limiting exposure to untrusted networks. 4. Enforce strict input validation and sanitization policies on any custom integrations or extensions interacting with Microsoft 365 Copilot to prevent malformed data inputs. 5. Educate users about the risk of interacting with suspicious content or links that could trigger the vulnerability. 6. Employ data loss prevention (DLP) tools to detect and block unauthorized data exfiltration attempts. 7. Review and tighten access controls and audit logs related to Microsoft 365 Copilot usage to facilitate rapid incident response. 8. Consider temporary disabling or limiting use of Microsoft 365 Copilot in highly sensitive environments until patches are available.