CVE-2025-30388 is a high-severity heap-based buffer overflow vulnerability (CWE-122) identified in Microsoft Office LTSC for Mac 2021, specifically version 16.0.1. Although the description references a Windows Win32K GRFX component, the vulnerability is reported in the Mac version of Microsoft Office LTSC 2021, indicating a possible shared or analogous graphics processing component susceptible to memory corruption. This vulnerability allows an unauthorized attacker to execute arbitrary code locally by exploiting a heap buffer overflow, which occurs when the application writes more data to a buffer located on the heap than it can hold. The CVSS v3.1 score is 7.8, reflecting high impact on confidentiality, integrity, and availability, with an attack vector requiring local access (AV:L), low attack complexity (AC:L), no privileges required (PR:N), but requiring user interaction (UI:R). The scope is unchanged (S:U), and the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H). The vulnerability is currently published with no known exploits in the wild and no patches publicly available yet. The flaw could be triggered by a maliciously crafted file or input processed by the vulnerable Office component, leading to memory corruption and potential arbitrary code execution. Given the local attack vector, exploitation requires the attacker to have local access to the target machine and to convince the user to interact with malicious content. The vulnerability’s presence in a widely used productivity suite on Mac platforms raises concerns about potential targeted attacks or lateral movement within enterprise environments.

For European organizations, this vulnerability poses a significant risk, especially for enterprises and institutions relying on Microsoft Office LTSC for Mac 2021 in their workflows. Successful exploitation could lead to unauthorized code execution, enabling attackers to escalate privileges, install malware, or exfiltrate sensitive data. The high impact on confidentiality, integrity, and availability means critical business documents and communications could be compromised or disrupted. Since the attack requires local access and user interaction, the threat is more pronounced in environments where endpoint security is weak or where users may be tricked into opening malicious files or links. Sectors such as finance, government, healthcare, and legal services in Europe, which handle sensitive information and often use Mac systems, could face operational disruptions and data breaches. Additionally, the lack of a patch at the time of disclosure increases the window of exposure, necessitating immediate mitigation efforts to prevent exploitation.

European organizations should implement a multi-layered mitigation strategy beyond generic advice: 1) Enforce strict endpoint security policies on Mac devices, including application whitelisting and behavior monitoring to detect anomalous Office application activities. 2) Educate users about the risks of opening unsolicited or suspicious Office documents, emphasizing the need for caution with files from unknown or untrusted sources. 3) Utilize network segmentation to limit the ability of attackers to gain local access or move laterally within the network. 4) Deploy advanced endpoint detection and response (EDR) solutions capable of identifying heap-based buffer overflow exploitation attempts or unusual memory behaviors. 5) Monitor for indicators of compromise related to Office processes and maintain up-to-date threat intelligence feeds. 6) Prepare for rapid deployment of patches once Microsoft releases an official fix, including testing in controlled environments to ensure compatibility. 7) Consider temporary restrictions on the use of Microsoft Office LTSC for Mac 2021 in high-risk environments until a patch is available.