CVE-2026-20666 is an authorization vulnerability identified in Apple macOS, specifically addressed in the macOS Tahoe 26.3 update. The root cause is an improper state management flaw in the authorization mechanism that governs access to sensitive user data. This flaw allows an application running with limited privileges (low privilege level) to bypass intended access controls and read sensitive information without requiring any user interaction. The vulnerability does not permit modification or deletion of data (no integrity or availability impact), but the confidentiality of user data is compromised. The CVSS vector (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N) indicates that the attack vector is local, with low attack complexity, requiring low privileges, no user interaction, and impacts confidentiality only. The vulnerability is categorized under CWE-285, which relates to improper authorization checks. Although no exploits have been reported in the wild, the potential for unauthorized data disclosure makes this a concern for organizations relying on macOS devices. The affected versions are unspecified, but the fix is included in macOS Tahoe 26.3, emphasizing the importance of timely patching. This issue highlights the criticality of robust state management in authorization logic to prevent privilege escalation and unauthorized data access.

The primary impact of CVE-2026-20666 is the unauthorized disclosure of sensitive user data on affected macOS systems. For organizations, this could lead to leakage of confidential information such as personal user data, credentials, or proprietary business information, potentially facilitating further attacks like social engineering or targeted intrusions. Since exploitation requires local access with low privileges, insider threats or malware that gains limited access could leverage this vulnerability to escalate data access without detection. The lack of impact on integrity and availability reduces the risk of system disruption but does not diminish the confidentiality risk. Organizations with macOS-dependent environments, especially those handling sensitive or regulated data, face increased risk of data breaches and compliance violations if unpatched. The absence of known exploits in the wild suggests limited immediate threat, but the vulnerability remains a significant risk if attackers develop exploit code. Overall, the vulnerability could undermine trust in macOS security and expose organizations to data exfiltration risks.

To mitigate CVE-2026-20666, organizations should prioritize updating all macOS devices to macOS Tahoe 26.3 or later, which contains the patch addressing the authorization state management flaw. Beyond patching, organizations should implement strict application control policies to limit the execution of untrusted or unnecessary applications, reducing the risk of local exploitation. Employ endpoint detection and response (EDR) solutions to monitor for unusual local privilege escalation attempts or unauthorized access to sensitive data. Enforce the principle of least privilege for user accounts and applications to minimize the attack surface. Regularly audit local user permissions and installed applications to detect potential vectors for exploitation. Additionally, educate users about the risks of installing unverified software and maintain robust physical security controls to prevent unauthorized local access. Since no user interaction is required for exploitation, automated monitoring for anomalous data access patterns can help detect exploitation attempts. Finally, maintain an up-to-date inventory of macOS devices and ensure timely deployment of security updates.