CVE-2025-29977 is a use-after-free vulnerability classified under CWE-416 found in Microsoft Excel, part of the Microsoft 365 Apps for Enterprise suite, specifically version 16.0.1. Use-after-free vulnerabilities occur when a program continues to use memory after it has been freed, leading to undefined behavior such as memory corruption. In this case, the vulnerability allows an attacker to execute arbitrary code locally on the victim's machine by crafting a malicious Excel file that triggers the flaw when opened. The vulnerability does not require any privileges or prior authentication but does require user interaction, such as opening a malicious document. The CVSS v3.1 base score is 7.8, indicating high severity, with vector metrics showing local attack vector (AV:L), low attack complexity (AC:L), no privileges required (PR:N), user interaction required (UI:R), unchanged scope (S:U), and high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). Although no known exploits are currently reported in the wild, the vulnerability is publicly disclosed and considered critical for organizations relying on Microsoft 365 Apps for Enterprise. The flaw could allow attackers to gain full control over affected systems, steal sensitive data, or disrupt operations. The vulnerability was reserved in March 2025 and published in May 2025. No patch links are currently provided, but organizations should monitor for updates from Microsoft. The vulnerability is enriched by CISA, indicating its importance in cybersecurity advisories.

For European organizations, the impact of CVE-2025-29977 is significant due to the widespread use of Microsoft 365 Apps for Enterprise across government, finance, healthcare, and critical infrastructure sectors. Successful exploitation could lead to local code execution, enabling attackers to escalate privileges, deploy ransomware, exfiltrate sensitive data, or disrupt business operations. The high impact on confidentiality, integrity, and availability means that data breaches, system downtime, and loss of trust are plausible consequences. Given the requirement for user interaction, phishing campaigns or malicious document distribution could be effective attack vectors. The lack of known exploits in the wild currently reduces immediate risk but does not diminish the urgency for mitigation, as attackers often develop exploits rapidly after public disclosure. European organizations with remote or hybrid work environments may face increased exposure due to document sharing practices. The vulnerability could also affect supply chains and third-party vendors using Microsoft 365 Apps, amplifying the risk.

1. Apply security updates from Microsoft immediately once patches for CVE-2025-29977 are released. 2. Until patches are available, implement application control policies to restrict execution of untrusted Excel macros and disable automatic content execution in Microsoft Office. 3. Employ advanced endpoint detection and response (EDR) solutions capable of detecting anomalous behavior indicative of use-after-free exploitation. 4. Conduct user awareness training focused on phishing and malicious document risks to reduce the likelihood of user interaction with crafted Excel files. 5. Utilize network segmentation to limit lateral movement if a system is compromised. 6. Monitor security advisories from Microsoft and CISA for updates and exploit reports. 7. Implement strict email filtering and sandboxing to detect and block malicious attachments. 8. Review and enforce least privilege principles for user accounts to minimize potential damage from local code execution. 9. Consider disabling legacy or unnecessary Office features that increase attack surface. 10. Maintain regular backups and test recovery procedures to mitigate ransomware or destructive attack impacts.