CVE-2026-20956 is a vulnerability classified under CWE-822 (Untrusted Pointer Dereference) found in Microsoft 365 Apps for Enterprise, specifically in Microsoft Excel version 16.0.1. This vulnerability arises when Excel dereferences a pointer that can be controlled or influenced by an attacker, leading to undefined behavior that can be exploited to execute arbitrary code locally. The flaw does not require any prior privileges (PR:N), but does require user interaction (UI:R), such as opening a malicious Excel file. The attack vector is local (AV:L), meaning the attacker needs local access to the system, but no authentication is required. The vulnerability affects confidentiality, integrity, and availability at a high level (C:H/I:H/A:H), potentially allowing an attacker to run code with the same privileges as the user, leading to data theft, corruption, or system compromise. The CVSS v3.1 base score is 7.8, indicating a high severity. No public exploits or patches are currently available, but the vulnerability is published and recognized by Microsoft. The vulnerability's root cause is the unsafe handling of pointers within Excel's codebase, which can be manipulated to redirect execution flow. This type of vulnerability is critical in environments where Excel files are frequently exchanged and trusted, as it can be leveraged for targeted attacks or malware deployment.

For European organizations, the impact of CVE-2026-20956 can be significant due to the widespread use of Microsoft 365 Apps in enterprises, government agencies, and critical infrastructure. Successful exploitation can lead to local code execution, enabling attackers to steal sensitive data, disrupt business operations, or establish persistence within networks. Given the high confidentiality, integrity, and availability impact, organizations handling sensitive financial, personal, or intellectual property data are at elevated risk. The requirement for local access and user interaction somewhat limits remote exploitation but does not eliminate risk, especially in environments with lax endpoint security or where phishing campaigns can deliver malicious Excel files. The lack of current exploits in the wild provides a window for proactive mitigation. However, once exploits emerge, the threat landscape could rapidly escalate, particularly targeting European organizations with high Microsoft 365 adoption and critical Excel usage.

1. Monitor Microsoft security advisories closely and apply official patches immediately once released to remediate the vulnerability. 2. Until patches are available, restrict local access to systems running Microsoft 365 Apps, especially Excel, by enforcing strict access controls and least privilege principles. 3. Implement application whitelisting and endpoint protection solutions that can detect or block suspicious behavior related to Excel processes. 4. Educate users about the risks of opening unsolicited or unexpected Excel files, emphasizing caution with email attachments and downloads. 5. Employ network segmentation to limit lateral movement if a local compromise occurs. 6. Use advanced threat protection tools that can sandbox or analyze Excel files before delivery to end users. 7. Regularly audit and update security policies to ensure compliance with best practices for endpoint security. 8. Consider disabling macros or other potentially risky Excel features if not required for business operations.