CVE-2025-59497 is a time-of-check to time-of-use (TOCTOU) race condition vulnerability identified in Microsoft Defender for Endpoint for Linux, specifically version 101.0.0. This vulnerability stems from a timing flaw where the software checks a resource or condition and then uses it without ensuring the state remains unchanged, allowing an attacker to manipulate the state between these operations. The flaw is categorized under CWE-367, indicating a race condition that can lead to inconsistent or unexpected behavior. An authorized attacker with local access and low privileges can exploit this vulnerability to cause a denial of service (DoS) by disrupting the normal operation of the Defender agent. The CVSS 3.1 score of 7.0 reflects a high severity, with attack vector local (AV:L), high attack complexity (AC:H), low privileges required (PR:L), no user interaction (UI:N), unchanged scope (S:U), and high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). Although no public exploits are currently known, the vulnerability poses a significant risk to endpoint security on Linux systems, potentially disabling or impairing Microsoft Defender’s protective functions and exposing systems to further compromise. The lack of a patch at the time of publication necessitates immediate attention to access controls and monitoring to mitigate exploitation risks.

For European organizations, this vulnerability could have serious consequences, especially those relying on Microsoft Defender for Endpoint on Linux servers for critical infrastructure, cloud environments, or enterprise security. A successful exploitation could lead to denial of service, effectively disabling endpoint protection and increasing exposure to malware, ransomware, or other cyberattacks. This disruption could affect confidentiality by allowing unauthorized data access if the protection is bypassed, integrity by enabling tampering with system files or security configurations, and availability by causing service outages. Organizations in sectors such as finance, healthcare, energy, and government, which often deploy Linux-based systems and rely on Microsoft security solutions, may face operational disruptions and compliance risks. The requirement for local access limits remote exploitation but highlights the need for strict internal access controls and monitoring of privileged users. The absence of known exploits provides a window for proactive defense, but the high impact score demands urgent mitigation.

1. Restrict local access to Linux systems running Microsoft Defender for Endpoint to trusted and authorized personnel only, employing strict user account management and privilege separation. 2. Monitor system logs and Defender agent behavior for anomalies that could indicate exploitation attempts or race condition triggers. 3. Implement mandatory access controls (e.g., SELinux, AppArmor) to limit the ability of processes and users to interfere with Defender’s operations. 4. Use file integrity monitoring to detect unexpected changes in Defender-related files or configurations. 5. Prepare for rapid deployment of patches or updates from Microsoft once available; subscribe to official security advisories for timely information. 6. Conduct internal audits and penetration testing focusing on local privilege escalation and race condition vulnerabilities to identify and remediate similar weaknesses. 7. Employ kernel-level security features and update the Linux kernel regularly to reduce the attack surface for race conditions. 8. Educate system administrators about the risks of TOCTOU vulnerabilities and the importance of minimizing local access and privilege misuse.