CVE-2026-92369 in Full Client
Summary
by MITRE • 09/29/2026
TeamViewer Full Client and Host prior to version 15.82 on Windows contain a TOCTOU race condition in the installer rollback mechanism. A local low-privileged attacker can replace rollback backup files stored in a user-writable temporary directory before they are restored by an elevated installer, resulting in privilege escalation to NT AUHORITY/SYSTEM. Exploitation requires successful timing of the race condition and a rollback during installation or update.
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Analysis
by VulDB Data Team • 09/30/2026
The vulnerability identified involves a Time-of-Check-to-Time-of-Use (TOCTOU) race condition within the installer rollback mechanism of TeamViewer Full Client and Host versions prior to 15.82 on Windows operating systems. This flaw stems from an insecure handling of temporary files during software installation or update processes, specifically when the system attempts to revert changes in case of failure. The core technical issue lies in the use of a user-writable temporary directory for storing rollback backup files. When the installer initiates a rollback sequence due to an error, it checks if specific backup files exist and then proceeds to restore them with elevated privileges. However, there is a critical window between the check and the actual file restoration where the operating system allows any local process access to modify or replace these files.
A local attacker with low-privileged account credentials can exploit this race condition by monitoring the temporary directory for the creation of rollback backup files. By rapidly replacing these legitimate backup files with maliciously crafted payloads, such as a pre-planted executable script or binary that executes arbitrary commands, the attacker forces the elevated installer to execute their code during the restoration process. Because the installation service runs with SYSTEM-level privileges, any code executed via this mechanism inherits those high-level permissions. Successful exploitation requires precise timing to ensure the malicious file is in place before the installer attempts to read and restore it, as well as a scenario where an update or installation triggers a rollback event, providing the necessary context for the privilege escalation vector to activate.
The operational impact of this vulnerability is severe, resulting in full system compromise through privilege escalation from a standard user account to NT AUTHORITY/SYSTEM. This level of access grants the attacker unrestricted control over the affected machine, including the ability to install additional malware, create new administrative accounts, modify security policies, and exfiltrate sensitive data without detection by standard endpoint protection mechanisms that rely on process integrity checks rather than file system race condition monitoring. The attack does not require physical interaction with the target beyond initial low-level access, making it a significant threat in environments where multiple users share systems or where remote desktop solutions like TeamViewer are frequently used for administrative tasks.
Mitigation strategies primarily involve upgrading to TeamViewer version 15.82 or later, which addresses this race condition by implementing secure temporary file handling practices such as using non-writable directories for rollback backups or employing atomic operations that prevent substitution during the check-and-use window. In environments where immediate patching is not feasible, administrators should restrict write permissions on system temporary directories to only trusted service accounts and monitor for unusual activity in these locations. Additionally, enforcing strict application control policies can help mitigate the risk by preventing unauthorized executables from running even if they are placed in vulnerable paths during installation processes. This vulnerability aligns with CWE-367 (TOCTOU Race Condition) and is categorized under MITRE ATT&CK technique T1059 Command and Scripting Interpreter, as it leverages system scripts or binaries to execute arbitrary code within a privileged context.