CVE-2026-27750 is a time-of-check time-of-use (TOCTOU) race condition vulnerability identified in the Optimizer component of Avira Internet Security by Gen Digital Inc. The vulnerability arises because a privileged service running with SYSTEM-level privileges performs a two-phase operation: first, it scans directories to identify candidates for cleanup, and second, it deletes these directories during a separate cleanup phase. Critically, the service does not revalidate the directory paths between these phases. This gap allows a local attacker to exploit the race condition by replacing a previously scanned directory with a symbolic link, junction, or reparse point that points to an unintended system location. When the privileged service proceeds to delete the directory, it inadvertently deletes files or directories outside the intended scope. This can result in deletion of protected system files, potentially causing denial of service or compromising system integrity. Furthermore, by deleting critical files or directories, an attacker may escalate privileges locally. The vulnerability requires local access but no elevated privileges or user interaction, making it relatively easy to exploit once local access is obtained. The CVSS 4.0 base score is 8.5 (high severity), reflecting the significant impact on confidentiality, integrity, and availability, combined with low attack complexity and no need for authentication. No patches or known exploits are currently reported, but the risk remains significant for affected systems.

The impact of CVE-2026-27750 is substantial for organizations using Avira Internet Security. Successful exploitation can lead to unintended deletion of critical system files or directories, resulting in denial of service conditions that disrupt business operations. The deletion of protected files can also compromise system integrity, potentially allowing attackers to escalate privileges locally and gain broader control over affected machines. This can facilitate further lateral movement or persistence within organizational networks. Since the vulnerability requires only local access, insider threats or attackers who have gained initial footholds can leverage this flaw to deepen their control. The disruption caused by deletion of system files may also necessitate costly recovery efforts, including system restoration or reinstallation. Organizations relying on Avira Internet Security for endpoint protection should consider this vulnerability a serious risk to endpoint stability and security posture.

To mitigate CVE-2026-27750, organizations should implement the following specific measures: 1) Restrict local user permissions strictly to prevent unauthorized users from gaining local access to systems running Avira Internet Security. 2) Monitor and control the creation of junctions, symbolic links, and reparse points by local users to reduce the risk of exploitation. 3) Employ application whitelisting and endpoint detection to detect suspicious activities involving directory manipulation. 4) Until a vendor patch is available, consider disabling or limiting the use of the Optimizer component if feasible, or run it with reduced privileges if configurable. 5) Implement file system integrity monitoring to detect unexpected deletions or modifications of critical system files. 6) Maintain regular backups and have tested recovery procedures to quickly restore systems if deletion occurs. 7) Stay alert for vendor advisories and apply patches promptly once released. 8) Conduct internal audits to identify systems running vulnerable versions of Avira Internet Security and prioritize them for remediation.