Description

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.force_share_accept 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.

Mitigation

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