National CERT Warns TeamViewer Users to Update Now Over Serious Flaw

The National Cyber Emergency Response Team (National CERT) has warned TeamViewer users to update their remote-access app immediately following the discovery of a critical flaw. The vulnerability, assigned CVE-2026-111585, carries a high severity rating of 8.8, according to the CVSS scoring system. The flaw impacts TeamViewer clients running versions prior to 15.83 on Windows, macOS, and Linux systems.

The National CERT explained that the bug stems from an integer overflow issue within the component responsible for handling remote screen data. By sending specially crafted data, an attacker could trigger the overflow, leading to either a crash or memory corruption within the TeamViewer application. Depending on the targeted platform, this could potentially grant the attacker the ability to execute malicious code with the same privileges as the application itself.

However, the attack requires a user to connect to a computer controlled by the attacker, thereby not functioning automatically.

Affected TeamViewer products include the Full Client for Windows, macOS, and Linux, the TeamViewer Portable version for Windows, and the Android Remote Control app. Users are advised to upgrade to version 15.83 or later. For those using older versions, separate patching solutions are available, such as 14.7.48868 for the 14.x branch, and 13.2.36231 for the 13.x branch.

National CERT recommended a series of steps for users and organizations to mitigate the risk. These include updating all TeamViewer installations, limiting remote access to only trusted individuals, restricting remote access to approved users and devices, and monitoring for any unexpected crashes or unusual session activities. Should patching not be immediately feasible, the advisory suggested blocking untrusted remote connections.

In cases where a device may be compromised, organizations were advised to preserve logs, restrict remote access, and seek assistance from incident response experts.