CVE-2025-21361 is a remote code execution vulnerability identified in Microsoft Office LTSC for Mac 2021, specifically impacting Microsoft Outlook. The root cause is an improper restriction of names for files and other resources (CWE-641), which can be exploited by an attacker who crafts malicious files or resources with specially crafted names. When a user interacts with such a file or resource, the vulnerability allows execution of arbitrary code with the privileges of the user running Outlook. The vulnerability requires user interaction (e.g., opening or previewing a malicious email or attachment) but does not require prior authentication, increasing its risk profile. The CVSS v3.1 score of 7.8 indicates high severity, with high impact on confidentiality, integrity, and availability. The attack vector is local (AV:L), meaning the attacker must have some form of access to deliver the malicious payload, typically via email or file sharing. The vulnerability is currently published but no known exploits have been reported in the wild, suggesting it is either newly discovered or not yet weaponized. The affected version is 16.0.1 of Microsoft Office LTSC for Mac 2021. The vulnerability highlights the risks associated with improper validation and restriction of file/resource names, which can be leveraged to bypass security controls and execute malicious code. Given the widespread use of Microsoft Outlook in enterprise environments, this vulnerability poses a significant threat to organizations relying on Mac platforms for email communications.

The potential impact of CVE-2025-21361 is substantial for organizations worldwide using Microsoft Office LTSC for Mac 2021, particularly Outlook. Successful exploitation can lead to full compromise of the affected user's system, including unauthorized access to sensitive emails, credentials, and other confidential data. The attacker can execute arbitrary code, potentially installing malware, ransomware, or establishing persistence. This threatens the confidentiality, integrity, and availability of organizational data and systems. Since Outlook is a primary communication tool, compromise can facilitate lateral movement within networks, data exfiltration, and disruption of business operations. The requirement for user interaction limits mass exploitation but targeted spear-phishing campaigns could be highly effective. The lack of known exploits in the wild currently reduces immediate risk, but the high severity score and ease of exploitation once a crafted file is delivered make this a critical vulnerability to address promptly. Organizations with Mac users in sensitive roles or industries face elevated risk, as attackers may exploit this vector to bypass traditional Windows-centric defenses.

To mitigate CVE-2025-21361, organizations should implement a multi-layered approach beyond waiting for official patches: 1) Enforce strict email filtering and attachment scanning to block or quarantine suspicious files with unusual or malformed names. 2) Educate users on the risks of opening unexpected or suspicious email attachments, emphasizing caution with files from unknown or untrusted sources. 3) Restrict or disable automatic previewing of email attachments in Outlook to reduce inadvertent triggering of the vulnerability. 4) Implement application whitelisting and endpoint protection solutions capable of detecting anomalous behaviors related to file handling and code execution. 5) Monitor network and endpoint logs for unusual activity indicative of exploitation attempts. 6) Where feasible, limit the use of Microsoft Office LTSC for Mac 2021 version 16.0.1 until patches are released. 7) Prepare incident response plans specific to email-borne attacks and remote code execution scenarios. 8) Once Microsoft releases a patch, prioritize rapid deployment across all affected systems. These targeted steps help reduce the attack surface and improve detection and response capabilities against exploitation attempts.