CVE-2026-20953 is a use-after-free vulnerability classified under CWE-416 found in Microsoft Office 2019 version 19.0.0. This vulnerability arises when the software improperly manages memory, specifically freeing memory that is still in use, which can lead to execution of arbitrary code by an attacker. The flaw allows an unauthorized attacker to execute code locally without requiring any privileges or user interaction, meaning an attacker with local access can exploit this vulnerability to gain control over the affected system. The vulnerability impacts confidentiality, integrity, and availability, potentially allowing attackers to read sensitive data, modify or delete information, and disrupt system operations. The CVSS v3.1 base score is 8.4, indicating high severity, with vector AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H, which means local attack vector, low attack complexity, no privileges or user interaction required, unchanged scope, and high impact on confidentiality, integrity, and availability. Although no public exploits are known at this time, the vulnerability poses a significant risk due to the widespread use of Microsoft Office 2019 in enterprise environments. The lack of available patches at the time of publication necessitates immediate attention to mitigation strategies. The vulnerability was reserved in December 2025 and published in January 2026, indicating recent discovery and disclosure.

For European organizations, this vulnerability presents a critical risk due to the widespread deployment of Microsoft Office 2019 across both private and public sectors. Successful exploitation could lead to full system compromise, allowing attackers to access sensitive corporate data, disrupt business operations, or use compromised systems as footholds for lateral movement within networks. Sectors such as finance, government, healthcare, and critical infrastructure are particularly vulnerable given their reliance on Office productivity tools and the sensitivity of their data. The local attack vector means that attackers need some form of local access, which could be achieved through physical access, compromised credentials, or other initial access methods. The absence of required user interaction lowers the barrier for exploitation once local access is obtained. This vulnerability could facilitate insider threats or attacks by malware that gains local execution capabilities. The high impact on confidentiality, integrity, and availability underscores the potential for severe operational and reputational damage, regulatory penalties under GDPR, and financial losses.

1. Restrict local access to systems running Microsoft Office 2019 to trusted users only, employing strict access controls and monitoring. 2. Implement application whitelisting and endpoint protection solutions that can detect and block suspicious code execution patterns related to use-after-free exploits. 3. Employ network segmentation to limit the spread of an attacker who gains local access to one system. 4. Monitor system logs and behavior analytics for unusual activity indicative of exploitation attempts, such as unexpected process launches or memory anomalies. 5. Until an official patch is released, consider disabling or restricting features in Office 2019 that are not essential and could be vectors for exploitation. 6. Educate users about the risks of local access compromise and enforce strong physical security policies. 7. Prepare for rapid deployment of patches once Microsoft releases them, including testing in controlled environments to ensure compatibility. 8. Use virtualization or sandboxing for opening untrusted Office documents to reduce risk exposure. 9. Regularly audit and update endpoint security configurations to ensure they are optimized against memory corruption exploits.