CVE-2025-43276 is a logic error vulnerability in Apple macOS specifically impacting the iCloud Private Relay feature, which is designed to enhance user privacy by routing internet traffic through multiple relays to obscure user IP addresses and browsing activity. The vulnerability manifests when more than one user is logged into the same macOS device concurrently, causing iCloud Private Relay to fail to activate. This failure results from improper error handling in the system's logic, leading to a denial of the privacy service rather than a direct compromise of data confidentiality or integrity. The CVSS v3.1 base score is 5.3 (medium), reflecting that the vulnerability can be exploited remotely without authentication or user interaction, but only impacts availability (denial of service of the privacy feature). The flaw is categorized under CWE-367 (Time-of-check Time-of-use (TOCTOU) race condition), indicating a timing or logic issue in state validation. The vulnerability was reserved in April 2025 and published in July 2025, with a fix delivered in macOS Sequoia 15.6. No known exploits have been reported in the wild, suggesting limited active exploitation. However, the impact on privacy services could be significant for users relying on iCloud Private Relay for anonymity and data protection, especially in multi-user environments such as shared workstations or public access devices.

For European organizations, the primary impact of CVE-2025-43276 is the potential loss of iCloud Private Relay functionality when multiple users share a macOS device. This reduces the privacy protections afforded by the service, potentially exposing user IP addresses and browsing metadata to network observers or adversaries. While the vulnerability does not directly lead to data breaches or system compromise, the diminished privacy can have regulatory implications under GDPR and other data protection laws, especially for organizations handling sensitive or personal data. Enterprises using shared macOS devices in offices, labs, or public kiosks may see increased risk of user activity exposure. Additionally, the denial of service of a privacy feature could undermine user trust and compliance with internal security policies. The lack of required authentication or user interaction means attackers could remotely trigger the issue, potentially disrupting privacy services at scale. However, since no known exploits exist, the immediate operational risk is moderate but warrants proactive remediation.

The most effective mitigation is to update all affected macOS devices to macOS Sequoia 15.6 or later, where the logic error has been corrected with improved error handling. Organizations should prioritize patch management for devices used in multi-user scenarios. Additionally, administrators should audit device usage policies to minimize concurrent multi-user logins on the same machine, especially on shared or public workstations. Where multi-user access is necessary, consider alternative privacy solutions or network-level protections to supplement iCloud Private Relay. Monitoring network traffic for anomalies or unexpected IP exposures can help detect potential privacy failures. User training on the importance of privacy features and prompt reporting of service disruptions can aid early detection. Finally, organizations should review compliance requirements related to user data privacy and document mitigation steps to demonstrate due diligence.