CVE-2026-104102: copyparty FTP: upload outside defined volumes (limited path traversal)
copyparty is a portable file server. Prior to 1.20.19, FTP upload path handling does not confine destinations to configured copyparty volumes. When FTP or FTPS is explicitly enabled, a low-privileged authenticated user can submit traversal paths during upload to create a new file outside configured volumes wherever the copyparty process has write permission. The attacker cannot read or overwrite files, the output name receives a randomized suffix, and copyparty does not execute the file; however, unrelated software on the same host could process the newly created file. This issue is fixed in version 1.20.19.
Other sources
The FTP and FTPS server -- if enabled -- would allow uploading to any folder that the copyparty process had permission to write to.
The FTP-server is default-disabled, and must be explicitly enabled in the config with global-option ftp or ftps to be affected. Additionally, SFTP was not affected at all; only FTP and FTPS.
This was not a full read/write path-traversal; it had the following limitations: Only applied to uploads; it was not possible to read/download existing files in this manner. The output filename was not fully controllable; a randomized suffix would always be appended to the filename. Existing files could not be overwritten or appended to; only new files could be created. Filesystem-permissions would prevent writing to system folders, as copyparty surely does not run as root in most deployments. Copyparty itself will not execute arbitrary files as code by default, so this vulnerability could not be used to execute arbitrary code through copyparty.
The main concern is the potential effect on other unrelated software which is running on the same system.
The severity is assuming the worst case (SC:H/SI:H), that the same machine is running some unrelated software that will execute new arbitrarily-named files as code, and that the copyparty process has sufficient privileges to write files into the config-folder of that unrelated software.
— GitHub
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
pip/copypartyto a version that resolves this vulnerability.Fixed in 1.20.19 - Upgrade
Upgrade
copypartyto a version that resolves this vulnerability.Fixed in 1.20.19
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Only deployments that explicitly enable FTP or FTPS are affected. The vulnerable upload handling applies to copyparty versions before 1.20.19.
What access does an attacker need?
An attacker needs low-privileged authenticated access to the FTP or FTPS service. No user interaction is required, and the attacker can submit traversal paths as part of an upload.
What can an attacker do outside configured volumes?
They can create a new file in locations where the copyparty process has write permission, even if those locations are outside configured copyparty volumes. They cannot use this issue to read files or overwrite existing files, and created filenames receive a randomized suffix.
What is the risk if the uploaded file is not executed by copyparty?
Copyparty does not execute the created file, but unrelated software on the same host may process it. Exposure therefore depends on whether writable locations accessible to the copyparty process are monitored or consumed by other software.
What should be done if an immediate upgrade is not possible?
Disable FTP and FTPS if they are not required, since they must be explicitly enabled for exploitation. Also restrict the copyparty process's write permissions so it cannot create files in sensitive locations outside intended volumes.