CVE-2023-21715 is a security feature bypass vulnerability identified in Microsoft Publisher, a component of Microsoft 365 Apps for Enterprise version 16.0.1. The vulnerability is classified under CWE-863, indicating improper authorization that allows bypassing security controls. The CVSS v3.1 base score is 7.3 (high), with vector AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H, meaning the attack requires local access, low complexity, limited privileges, and user interaction, but can impact confidentiality, integrity, and availability substantially. The flaw enables an attacker to circumvent security mechanisms designed to protect document content or execution environments, potentially allowing execution of malicious code or unauthorized access to sensitive data. Although no public exploits have been reported, the vulnerability’s characteristics suggest it could be leveraged in targeted attacks, especially in environments where Microsoft Publisher documents are exchanged. The vulnerability was reserved in December 2022 and published in February 2023, but no patch links are currently provided, indicating that organizations must monitor for updates. The vulnerability’s exploitation could lead to full system compromise or data leakage, making it critical to address in enterprise environments.

For European organizations, this vulnerability poses a significant threat due to the widespread use of Microsoft 365 Apps for Enterprise across public and private sectors. Successful exploitation could lead to unauthorized disclosure of sensitive information, alteration or destruction of critical data, and disruption of business operations. Sectors such as government, finance, healthcare, and critical infrastructure are particularly at risk given their reliance on Microsoft productivity tools and the sensitivity of their data. The requirement for local access and user interaction somewhat limits remote mass exploitation but does not eliminate risk from phishing or social engineering campaigns that trick users into opening malicious Publisher files. The high impact on confidentiality, integrity, and availability means that exploitation could result in severe operational and reputational damage, regulatory penalties under GDPR, and financial losses. The absence of known exploits currently provides a window for proactive mitigation.

Organizations should prioritize the following mitigations: 1) Monitor Microsoft security advisories closely and apply patches or updates as soon as they become available for Microsoft 365 Apps, specifically targeting Publisher. 2) Implement strict user privilege management to limit local access and reduce the ability of attackers to leverage low-privilege accounts. 3) Enhance email and document filtering to detect and block potentially malicious Publisher files, including sandboxing attachments to analyze behavior before delivery. 4) Conduct user awareness training focused on recognizing phishing attempts and suspicious document interactions to reduce the risk of user interaction exploitation. 5) Employ endpoint detection and response (EDR) solutions to monitor for anomalous activities related to document processing or privilege escalation attempts. 6) Restrict macro execution and other scripting capabilities within Publisher documents where feasible. 7) Maintain regular backups and incident response plans to quickly recover from potential compromises.