Hi there,
It seems people with the direct link can download / view attachments that would have been otherwise not shown to users.
For example, if you uploaded an attachment to EXP00001 and the direct link to the file becomes
http://192.168.0.1/files/EXP00001-Attachment.pdf
Anyone who knows the above URL would be able to access the attachment directly without any authentication. Suggest to check sessions when accessing the /files/ and also check the user’s permission to whether he/she has access to that specific record, e.g. expense claim.
Tested on ERPNext: v5.6.2