CVE-2026-20618 is a vulnerability identified in Apple macOS that arises from improper handling of temporary files, categorized under CWE-377 (Insecure Temporary File). This flaw allows an application with limited privileges (PR:L) to potentially access sensitive user data stored in temporary files that are not adequately protected. The vulnerability does not require user interaction (UI:N) and affects confidentiality (C:H) but does not impact integrity or availability (I:N/A:N). The attack vector is local (AV:L), meaning an attacker must have local access to the system to exploit the issue. The vulnerability was addressed in macOS Tahoe 26.3 by improving the handling and security of temporary files, preventing unauthorized access to sensitive data. Although no known exploits have been reported in the wild, the vulnerability poses a risk to user privacy and data confidentiality. The CVSS v3.1 base score is 5.5, reflecting a medium severity level. The vulnerability's root cause is linked to insecure temporary file management, which can lead to information disclosure if exploited by a malicious app or actor with local access.

The primary impact of CVE-2026-20618 is the unauthorized disclosure of sensitive user data on affected macOS systems. This can lead to privacy violations, leakage of personal or corporate confidential information, and potential follow-on attacks if the disclosed data includes credentials or other sensitive artifacts. Since exploitation requires local access with low privileges, the threat is more relevant in scenarios where an attacker gains physical or remote access to a user’s machine, such as through social engineering, insider threats, or malware that operates with limited privileges. The vulnerability does not affect system integrity or availability, so it does not directly enable system compromise or denial of service. However, the exposure of sensitive data can undermine trust in affected systems and may have regulatory or compliance implications for organizations handling sensitive information. Organizations relying heavily on macOS devices for sensitive operations or data storage are at increased risk.

To mitigate CVE-2026-20618, organizations and users should promptly update all affected macOS systems to version Tahoe 26.3 or later, where the vulnerability has been addressed. Beyond patching, organizations should enforce strict application control policies to limit the installation and execution of untrusted or unnecessary applications, reducing the risk of local exploitation. Employ endpoint detection and response (EDR) solutions capable of monitoring suspicious local file access patterns, particularly around temporary files. Implement least privilege principles to restrict user and application permissions, minimizing the potential impact of compromised or malicious apps. Regularly audit and monitor local user activities and file system permissions to detect anomalies. Additionally, educate users about the risks of installing untrusted software and the importance of physical security to prevent unauthorized local access. Since no known exploits exist in the wild, proactive patching and access control remain the most effective defenses.