CVE-2026-20618 is a vulnerability identified in Apple macOS that arises from improper handling of temporary files, classified under CWE-377 (Insecure Temporary File). This flaw allows an application running with limited privileges (local access and low complexity) to access sensitive user data that it should not normally be able to read. The vulnerability does not require user interaction, making it easier to exploit once local access is obtained. The issue was addressed by Apple through improved temporary file handling in macOS Tahoe 26.3, which mitigates the risk of unauthorized data exposure. The CVSS v3.1 base score is 5.5 (medium severity), reflecting high confidentiality impact but no impact on integrity or availability. The attack vector is local (AV:L), requiring low privileges (PR:L), and no user interaction (UI:N). The vulnerability does not affect system integrity or availability, limiting the scope to confidentiality breaches. No public exploits have been reported, but the vulnerability poses a risk especially in environments where multiple users or applications coexist on the same macOS system. The root cause relates to insecure temporary file creation or management, which can lead to unauthorized file access or information disclosure.

The primary impact of CVE-2026-20618 is unauthorized disclosure of sensitive user data on affected macOS systems. This can lead to privacy violations, leakage of confidential information such as credentials, personal files, or application data. While the vulnerability does not compromise system integrity or availability, the confidentiality breach can have serious consequences for individuals and organizations, including identity theft, corporate espionage, or compliance violations. Organizations with multi-user macOS environments or those running untrusted applications locally are at higher risk. Since exploitation requires local access and low privileges, attackers who gain foothold on a system (e.g., via phishing or physical access) could escalate data access capabilities. The absence of user interaction requirement increases the likelihood of stealthy exploitation. Although no known exploits exist currently, the vulnerability should be considered a significant privacy risk until patched.

To mitigate CVE-2026-20618, organizations and users should promptly update affected macOS systems to version Tahoe 26.3 or later, where the vulnerability is fixed. Beyond patching, administrators should enforce strict application control policies to limit installation and execution of untrusted or unnecessary applications, reducing the risk of local exploitation. Employing endpoint security solutions that monitor file system access and detect anomalous behavior related to temporary files can help identify exploitation attempts. Restricting local user privileges and enforcing the principle of least privilege minimizes the attack surface. Additionally, educating users about the risks of running untrusted software and maintaining physical security of devices can reduce the likelihood of local attackers gaining access. Regular audits of temporary file handling and permissions on macOS systems can also help detect misconfigurations that might be exploited.