CVE-2025-29823 is a high-severity use-after-free vulnerability (CWE-416) found in Microsoft Office Excel, part of the Microsoft 365 Apps for Enterprise suite, specifically affecting version 16.0.1. This vulnerability allows an unauthorized attacker to execute arbitrary code locally by exploiting improper memory management in Excel. A use-after-free flaw occurs when a program continues to use a pointer after the memory it points to has been freed, potentially leading to memory corruption, crashes, or arbitrary code execution. In this case, the attacker can craft a malicious Excel file that, when opened by a user, triggers the vulnerability. The CVSS v3.1 base score is 7.8, indicating high severity, with the vector AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C. This means the attack requires local access (local vector), low attack complexity, no privileges required, but user interaction is necessary (opening the malicious file). The impact on confidentiality, integrity, and availability is high, as successful exploitation can lead to full code execution under the context of the user, potentially allowing installation of malware, data theft, or system compromise. There are no known exploits in the wild at the time of publication, and no patch links have been provided yet, indicating that organizations should be vigilant and prepare to apply updates once available. The vulnerability was reserved on March 11, 2025, and published on April 8, 2025, showing a recent discovery and disclosure timeline.

For European organizations, this vulnerability poses a significant risk due to the widespread use of Microsoft 365 Apps for Enterprise across various sectors including government, finance, healthcare, and critical infrastructure. Successful exploitation can lead to local code execution, enabling attackers to escalate privileges, move laterally within networks, and exfiltrate sensitive data. Given the high confidentiality, integrity, and availability impact, organizations could face data breaches, operational disruptions, and reputational damage. The requirement for user interaction (opening a malicious Excel file) suggests phishing or social engineering campaigns could be used to deliver the exploit, a common attack vector in Europe. Additionally, the lack of a patch at this time increases the window of exposure. Organizations handling sensitive personal data under GDPR must be particularly cautious to avoid regulatory penalties resulting from breaches stemming from this vulnerability.

1. Implement strict email filtering and attachment scanning to detect and block malicious Excel files, reducing the risk of phishing-based delivery. 2. Educate users on the risks of opening unsolicited or suspicious Excel documents, emphasizing verification of sender identity. 3. Employ application control or whitelisting solutions to restrict execution of unauthorized or unexpected code within Microsoft 365 Apps. 4. Utilize endpoint detection and response (EDR) tools to monitor for anomalous behaviors indicative of exploitation attempts. 5. Regularly back up critical data and ensure backups are isolated to enable recovery in case of compromise. 6. Monitor Microsoft security advisories closely for the release of patches or mitigations and prioritize rapid deployment once available. 7. Consider disabling or restricting macros and other advanced Excel features that could be leveraged in exploitation until the vulnerability is patched. 8. Apply the principle of least privilege to limit user permissions, minimizing the impact of local code execution.