CVE-2025-43506 is a logic error vulnerability identified in Apple macOS that affects the activation of iCloud Private Relay when more than one user is logged in simultaneously on the same system. iCloud Private Relay is a privacy feature designed to obscure user IP addresses and browsing activity by routing traffic through multiple relays, enhancing user anonymity and security. The vulnerability arises from improper error handling in the system's logic, which prevents iCloud Private Relay from activating under multi-user login conditions. This failure means that user traffic may not be routed through Private Relay, potentially exposing IP addresses and browsing data to network observers or ISPs, thereby degrading user privacy. The issue was resolved by Apple in macOS Tahoe 26.1 through improved error handling mechanisms. The affected versions are unspecified, but the fix is included in the latest macOS release. There are no known exploits in the wild, indicating that the vulnerability has not been actively leveraged by attackers. The vulnerability does not appear to allow privilege escalation, code execution, or direct compromise of system integrity but impacts confidentiality by disabling a key privacy feature. The flaw is particularly relevant for environments where multiple users share a single macOS device and log in concurrently, such as educational institutions, enterprises with shared workstations, or public access terminals. Since the vulnerability is logic-based and requires specific multi-user login conditions, exploitation complexity is moderate. No CVSS score is provided, but the nature of the vulnerability suggests a moderate impact primarily on privacy rather than system security.

For European organizations, the primary impact of CVE-2025-43506 is the potential reduction in user privacy due to the failure of iCloud Private Relay to activate when multiple users are logged in simultaneously. This could lead to exposure of user IP addresses and browsing activity to network observers, ISPs, or malicious actors on the network, undermining confidentiality protections. Organizations relying on macOS devices in shared environments—such as universities, research institutions, and enterprises with hot-desking or shared workstations—may see increased privacy risks for their users. Although the vulnerability does not enable direct system compromise or data integrity attacks, the loss of privacy protections could have regulatory implications under GDPR and other European privacy laws if user data is exposed. Additionally, organizations that emphasize strong privacy postures may face reputational risks. The absence of known exploits reduces immediate risk, but the vulnerability should be addressed promptly to maintain privacy guarantees. The impact is less severe for single-user devices or environments where users do not log in concurrently.

To mitigate CVE-2025-43506, European organizations should prioritize updating all macOS devices to macOS Tahoe 26.1 or later, where the issue is fixed. IT administrators should audit environments where multiple users log in concurrently on the same macOS device, such as shared workstations or lab computers, and consider limiting simultaneous logins if feasible. Implementing user session management policies to avoid concurrent sessions can reduce exposure. Organizations should also monitor network traffic for signs of unprotected browsing activity that would normally be routed through iCloud Private Relay. Educating users about the privacy implications of shared device usage and encouraging individual device use where possible can further reduce risk. Finally, integrating macOS update management into existing patch management workflows will ensure timely deployment of security fixes. Since no known exploits exist, proactive patching and operational controls are sufficient to mitigate this vulnerability.