Executive brief
Copyparty, a file-sharing server, contains a vulnerability where an attacker with existing file-upload permissions can execute malicious code in another user's browser. By uploading a specifically named file and tricking a victim into clicking a crafted link, the attacker could perform actions on the server using the victim's account. This could lead to unauthorized file deletion, movement, or the uploading of new files.
Technical details
A Cross-Site Scripting (XSS) vulnerability exists in Copyparty due to improper neutralization of input during web page generation. If an attacker has read and write permissions, they can upload a file named '.prologue.html'. While executing JavaScript when directly accessing this file is intended, the vulnerability allows the file to be evaluated when a victim visits a crafted folder URL (e.g., '/folder/?b'). Exploitation requires the victim to click a specific link, and impact is mitigated by strict SameSite cookie policies, meaning the link must typically be clicked from a page served by the same server. If successful, the attacker can execute arbitrary JavaScript in the victim's session to manipulate files. This is fixed in version 1.20.12.
Affected products
- 9001 copyparty < 1.20.12
Timeline
- 2026-03-11: disclosed
- 2026-03-12: advisory: GitHub Advisory published
- 2026-03-12: patched