TOCTOU Vulnerability in Avira Optimizer Enables Privilege Escalation

Executive Summary

CVE-2026-27750 is a time-of-check time-of-use (TOCTOU) race condition vulnerability found in the Optimizer component of Avira Internet Security.

A privileged service running with SYSTEM-level permissions first identifies directories for cleanup during a scan phase and later deletes them in a separate cleanup phase without revalidating the target paths.

A local attacker can exploit the time gap between these phases by replacing a previously scanned directory with a junction or reparse point before deletion occurs.

This causes the privileged process to delete unintended system locations, including protected files or directories.

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Impact Analysis

The vulnerability can lead to deletion of protected files or directories by a privileged process.

This may result in local privilege escalation, denial of service, or compromise of system integrity depending on the affected target.

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Compliance Impact

I don't know

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Detection Guidance

I don't know

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Mitigation Strategies

[{'type': 'paragraph', 'content': "To mitigate the CVE-2026-27750 vulnerability, it is important to prevent exploitation of the TOCTOU race condition in Avira Internet Security's Optimizer component."}, {'type': 'list_item', 'content': 'Avoid running the vulnerable Avira Internet Security versions until a patch or update is applied.'}, {'type': 'list_item', 'content': 'Check for and apply any security updates or patches provided by Avira that address this vulnerability.'}, {'type': 'list_item', 'content': 'Limit local user permissions to reduce the risk of a local attacker exploiting the vulnerability.'}, {'type': 'list_item', 'content': 'Monitor system directories for suspicious junctions or reparse points that could be used to exploit the deletion process.'}] [1]

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