GHSA-c4jr-5q7w-f6r9: SiYuan has Arbitrary File Write via /api/file/copyFile leading to RCE

The /api/file/copyFile endpoint does not validate the dest parameter, allowing authenticated users to write files to arbitrary locations on the filesystem. This can lead to Remote Code Execution (RCE) by writing to sensitive locations such as cron jobs, SSH authorized_keys, or shell configuration files.

• Affected Version: 3.5.3 (and likely all prior versions)