Group-Office is an enterprise customer relationship management and groupware tool. Prior to versions 6.8.155, 25.0.88, and 26.0.10, there is a reflected XSS vulnerability in GroupOffice on the external/index flow. The f parameter (Base64 JSON) is decoded and then injected into an inline JavaScript block without strict escaping, allowing </script><script>...</script> injection and arbitrary JavaScript execution in the victim's browser. This issue has been patched in versions 6.8.155, 25.0.88, and 26.0.10.