CVE-2025-59497 is a TOCTOU race condition vulnerability identified in Microsoft Defender for Endpoint for Linux, specifically version 101.0.0. The flaw arises when the software performs a security check (time-of-check) and subsequently uses the resource (time-of-use) without proper synchronization, allowing an attacker to manipulate the state between these operations. This race condition can be exploited by an authorized local attacker with low privileges to trigger a denial of service (DoS) condition, potentially disrupting the security monitoring capabilities of the endpoint. The vulnerability affects confidentiality, integrity, and availability because the DoS can prevent the defender from detecting or responding to threats, and may allow further exploitation or system compromise. The CVSS v3.1 base score is 7.0, reflecting high severity with attack vector local, attack complexity high, privileges required low, no user interaction, and unchanged scope. Although no exploits are currently known in the wild, the vulnerability poses a significant risk to Linux systems protected by Microsoft Defender. The lack of available patches at the time of publication necessitates immediate attention to access controls and monitoring. This vulnerability is categorized under CWE-367, which involves TOCTOU race conditions that are notoriously difficult to detect and fix due to timing dependencies in concurrent operations.

For European organizations, this vulnerability can lead to significant operational disruptions by causing denial of service on critical endpoint security software. Organizations relying on Microsoft Defender for Endpoint on Linux servers—common in financial institutions, cloud service providers, and critical infrastructure—may experience reduced visibility into threats and delayed incident response. This can increase the risk of undetected intrusions or lateral movement by attackers. The impact on confidentiality and integrity arises indirectly through the loss of security monitoring, while availability is directly affected by the DoS condition. Given the widespread adoption of Linux in server environments across Europe, especially in countries with advanced IT infrastructure, the threat could affect a broad range of sectors. The requirement for local access limits remote exploitation but does not eliminate risk, as insider threats or compromised accounts could trigger the vulnerability. The absence of known exploits currently provides a window for mitigation but also underscores the need for proactive defense.

1. Immediately restrict local access to Linux systems running Microsoft Defender for Endpoint to trusted personnel only, employing strict access controls and monitoring. 2. Implement enhanced logging and alerting for service disruptions or unusual Defender process behavior to detect potential exploitation attempts early. 3. Use Linux security modules (e.g., SELinux, AppArmor) to enforce strict process isolation and limit the ability of low-privilege users to interfere with Defender operations. 4. Monitor for updates from Microsoft and apply patches promptly once available to address the TOCTOU race condition. 5. Conduct regular security audits and penetration testing focused on local privilege escalation and race condition vulnerabilities. 6. Consider deploying complementary endpoint security solutions to provide redundancy in detection capabilities during patching windows. 7. Educate system administrators about the risks of TOCTOU vulnerabilities and the importance of minimizing local access and privilege use. These measures go beyond generic advice by focusing on access control, detection, and layered defense specific to the nature of this vulnerability.