CVE-2025-43521 is a security vulnerability identified in Intel-based Apple macOS systems. The core issue stems from a downgrade vulnerability that allowed applications to bypass certain security controls, specifically related to code-signing enforcement. Code-signing is a critical security mechanism that ensures only trusted and verified software can execute with certain privileges. The downgrade flaw permitted an attacker to circumvent these restrictions, enabling an app to access sensitive user data that should otherwise be protected. Apple addressed this vulnerability by implementing additional code-signing restrictions in macOS Sequoia 15.7.3, effectively closing the bypass vector. The vulnerability affects unspecified versions of macOS on Intel hardware, indicating that any unpatched system prior to 15.7.3 could be vulnerable. While no public exploits have been reported, the potential for data exposure is significant given the nature of the flaw. The vulnerability primarily impacts confidentiality, as unauthorized apps could read sensitive information without proper authorization. Exploitation likely requires the attacker to have the ability to run or install an app on the target system, but does not appear to require user interaction beyond that. This vulnerability highlights the importance of strict code-signing enforcement and the risks posed by downgrade attacks that weaken security controls.

For European organizations, the impact of CVE-2025-43521 can be substantial, particularly for those relying on Intel-based Macs for sensitive operations. The vulnerability allows unauthorized applications to access sensitive user data, potentially leading to data breaches involving personal information, intellectual property, or confidential business data. This could result in regulatory non-compliance, especially under GDPR, which mandates strict protection of personal data. The breach of confidentiality may also damage organizational reputation and trust. Since the vulnerability affects the core operating system's security enforcement, it could facilitate further attacks or lateral movement within networks if exploited. Organizations in sectors such as finance, healthcare, and government, which handle highly sensitive data, are at elevated risk. The absence of known exploits in the wild provides a window for proactive mitigation, but the ease of exploitation by a malicious app underscores the urgency of patching. Additionally, the vulnerability could be leveraged in targeted attacks or supply chain compromises where malicious apps are introduced into trusted environments.

European organizations should immediately verify the macOS version on all Intel-based Apple devices and prioritize upgrading to macOS Sequoia 15.7.3 or later, where the vulnerability is fixed. Implement strict application control policies to restrict installation and execution of untrusted or unsigned applications, leveraging Apple’s Gatekeeper and MDM solutions where possible. Employ endpoint detection and response (EDR) tools to monitor for suspicious app behavior indicative of exploitation attempts. Educate users about the risks of installing unauthorized software and enforce least privilege principles to limit app capabilities. Regularly audit installed applications and remove any that are unnecessary or untrusted. Network segmentation can help contain potential breaches originating from compromised devices. Finally, maintain up-to-date backups and incident response plans tailored to macOS environments to ensure rapid recovery if exploitation occurs.