The Nextcloud Desktop Client is a tool to synchronize files from Nextcloud Server with your computer. In version 3.6.0, if a user received a malicious file share and has it synced locally or the virtual filesystem enabled and clicked a nc://open/ link it will open the default editor for the file type of the shared file, which on Windows can also sometimes mean that a file depending on the type, e.g. "vbs", is being executed. It is recommended that the Nextcloud Desktop client is upgraded to version 3.6.1. As a workaround, users can block the Nextcloud Desktop client 3.6.0 by setting the minimum.supported.desktop.version system config to 3.6.1 on the server, so new files designed to use this attack vector are not downloaded anymore. Already existing files can still be used. Another workaround would be to enforce shares to be accepted by setting the sharing.forceshareaccept system config to true on the server, so new files designed to use this attack vector are not downloaded anymore. Already existing shares can still be abused.

The Nextcloud Desktop Client is a tool to synchronize files from Nextcloud Server with a computer. The Nextcloud Desktop Client invokes its uninstaller script when being installed to make sure there are no remnants of previous installations. In versions 3.0.3 through 3.2.4, the Client searches the Uninstall.exe file in a folder that can be written by regular users. This could lead to a case where a malicious user creates a malicious Uninstall.exe, which would be executed with administrative privileges on the Nextcloud Desktop Client installation. This issue is fixed in Nextcloud Desktop Client version 3.3.0. As a workaround, do not allow untrusted users to create content in the C:\ system folder and verify that there is no malicious C:\Uninstall.exe file on the system.

A code injection in Nextcloud Desktop Client 2.6.2 for macOS allowed to load arbitrary code when starting the client with DYLDINSERTLIBRARIES set in the environment.

Nextcloud Desktop Client before 3.3.1 is vulnerable to improper certificate validation due to lack of SSL certificate verification when using the "Register with a Provider" flow.

Nextcloud Desktop is the desktop sync client for Nextcloud. Prior to 3.16.5, when trying to manually lock a file inside an end-to-end encrypted directory, the path of the file was sent to the server unencrypted, making it possible for administrators to see it in log files. This vulnerability is fixed in 3.16.5.