Reusing a Nonce, Key Pair in Encryption
The Nextcloud Desktop Client is a tool to synchronize files from Nextcloud Server. Starting with version 3.0.0 and prior to version 3.6.5, a malicious server administrator can recover and modify the contents of end-to-end encrypted files. Users should upgrade the Nextcloud Desktop client to 3.6.5 to receive a patch. No known workarounds are available.
CWE-323 - Reusing a Nonce, Key Pair in Encryption
Nonces should be used for the present occasion and only once.