CVE-2025-43506 is a logic error vulnerability in Apple macOS's iCloud Private Relay feature, which is designed to enhance user privacy by routing internet traffic through multiple relays to obscure user IP addresses and location. The vulnerability occurs when more than one user is logged into the same macOS device simultaneously, causing iCloud Private Relay to fail to activate due to improper error handling. This failure means that the affected users' internet traffic is no longer anonymized or protected by Private Relay, exposing them to potential network surveillance or tracking. The issue is categorized under CWE-843 (Access of Resource Using Incompatible Type or Version), indicating a logic flaw in managing user sessions or state. The vulnerability has a CVSS 3.1 base score of 7.5, reflecting its network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), high confidentiality impact (C:H), and no impact on integrity or availability (I:N/A:N). The flaw was addressed by Apple in macOS Tahoe 26.1 through improved error handling to ensure Private Relay activates correctly even with multiple concurrent users. No public exploits have been reported, but the vulnerability could be exploited remotely without authentication, making it a significant privacy risk for users sharing devices or environments where multiple logins occur. The lack of patch links suggests users should update to the latest macOS version as soon as it becomes available.

For European organizations, this vulnerability primarily threatens user privacy and confidentiality of network traffic. In environments such as shared workstations, educational institutions, or organizations where multiple users log into the same macOS device, iCloud Private Relay may not activate, exposing users' IP addresses and browsing activity to network observers or malicious actors. This could lead to targeted surveillance, profiling, or interception of sensitive communications. Although the vulnerability does not affect data integrity or system availability, the loss of privacy protections can have regulatory and reputational consequences, especially under GDPR and other European data protection laws. Organizations relying on macOS devices for secure communications or remote work may face increased risk of data leakage. The absence of known exploits reduces immediate threat but does not eliminate risk, as attackers could develop exploits given the public disclosure. The impact is more pronounced in sectors with high macOS usage and multi-user device policies.

European organizations should prioritize updating all macOS devices to macOS Tahoe 26.1 or later once available to ensure the fix is applied. Until patching is complete, organizations should audit and limit multi-user concurrent logins on macOS devices, especially those used in shared environments like labs or kiosks. Implement device usage policies that discourage or prevent simultaneous user sessions to maintain Private Relay functionality. Network monitoring should be enhanced to detect anomalous traffic patterns that might indicate Private Relay is inactive. Additionally, organizations can educate users about the privacy implications and encourage use of personal devices or separate user sessions. For critical environments, consider deploying endpoint security solutions that verify the activation status of privacy features like Private Relay. Finally, maintain awareness of Apple security advisories for any updates or additional mitigations.