The threat concerns a Use After Free (UAF) vulnerability in Microsoft Excel, identified as CVE-2025-27751. This vulnerability affects Microsoft Excel 2016 and Microsoft Office Online Server with update KB5002699. The exploit leverages a memory management flaw where Excel improperly handles memory, leading to a use-after-free condition. An attacker can craft a malicious DOCX file containing embedded exploit code that, when opened by a user in Excel, triggers the vulnerability. This results in local code execution on the victim's Windows machine. The exploit is delivered via common vectors such as email attachments or streaming servers, relying on social engineering to convince users to open the malicious document. Once executed, the attacker can run arbitrary code with the privileges of the user, potentially leading to full system compromise, installation of malware, or other malicious activities. The exploit code is available publicly and is written in Perl, indicating that the attack can be automated or integrated into larger attack frameworks. Although the published severity is marked as medium, the exploit author describes the vulnerability as high-critical, highlighting the potential for severe impact. The vulnerability requires local execution, meaning the attacker must convince the user to open the malicious file, but no authentication is needed beyond user interaction. No official patches or mitigations are listed in the provided data, and no known exploits in the wild have been reported yet. The exploit code sample provided is a VBA macro stub, demonstrating how an attacker might embed malicious commands to execute arbitrary programs on the victim's machine.

For European organizations, this vulnerability poses a significant risk due to the widespread use of Microsoft Excel in business, government, and critical infrastructure sectors. Successful exploitation can lead to unauthorized code execution, enabling attackers to install persistent malware, steal sensitive data, disrupt operations, or move laterally within networks. The local execution nature means that phishing campaigns or malicious document distribution remain the primary attack vectors, which are common and effective. Given the integration of Excel in many workflows and the prevalence of Office 365 and legacy Excel versions, the attack surface is broad. Industries such as finance, healthcare, government agencies, and manufacturing, which rely heavily on Excel for data processing and reporting, are particularly vulnerable. The lack of patches and the availability of exploit code increase the urgency for mitigation. Additionally, the potential for this exploit to be used in targeted attacks or ransomware campaigns could have severe operational and reputational consequences for European entities.

1. Implement strict email filtering and attachment scanning to detect and block malicious DOCX files, especially those containing macros or unusual embedded content. 2. Enforce macro security policies in Microsoft Office, such as disabling macros by default and only allowing signed macros from trusted publishers. 3. Educate users on the risks of opening unsolicited or unexpected Excel documents, emphasizing verification of sender identity and cautious handling of email attachments. 4. Deploy endpoint detection and response (EDR) solutions capable of identifying suspicious process creation and script execution triggered by Office applications. 5. Apply application whitelisting to restrict execution of unauthorized programs that could be launched via malicious macros. 6. Monitor network traffic for unusual outbound connections that may indicate post-exploitation activity. 7. Maintain up-to-date backups and incident response plans to quickly recover from potential compromises. 8. Engage with Microsoft security advisories regularly to apply patches promptly once available. 9. Use sandboxing or virtualized environments to open untrusted documents safely when necessary. 10. Consider disabling legacy Office features that are not required, reducing the attack surface.