Copyparty is a portable file server. Prior to 1.20.12, if an attacker has been given both read- and write-permissions to the server, they can upload a malicious file with the filename .prologue.html and then craft a link to potentially execute arbitrary JavaScript in the victim's context. Note that it is intended behavior that the JavaScript would execute if the target clicks a link to the HTML file itself; "https://example.com/foo/.prologue.html". The vulnerability is that "https://example.com/foo/?b" would also evaluate the file, making the behavior unexpected. There are existing preventative measures (strict SameSite cookies) which makes it harder to leverage this vulnerability in an attack; in order to gain control of the target's authenticated session, the link must be clicked from a page served by the server itself -- most likely by editing an existing resource, which would require additional access permissions. Finally, for this attack to be successful, the attacker's target must click the specific crafted link given by the attacker. This vulnerability is not activated by normally browsing the web-UI on the server. This vulnerability is fixed in 1.20.12.

Copyparty is a portable file server. Prior to 1.20.12, there was a missing permission-check in the shares feature (the shr global-option). This vulnerability only applies when the shares feature is used for the specific purpose of creating a share of just a single file inside a folder or either the FTP or SFTP server is enabled, and also made publicly accessible. Given these conditions, when a user is browsing a share through either FTP or SFTP (not http or https), they can gain read-access to the remaining files inside the shared folder by guessing/bruteforcing the filenames. It was not possible to descend into subdirectories in this manner; only the sibling files were accessible. This vulnerability is similar to CVE-2025-58753 which was previously fixed for HTTP and HTTPS, but not for FTP. The FTPS server did not yet exist at that time. This vulnerability is fixed in 1.20.12.