CVE-2025-66284 Cross-site scripting in GroupSession Free edition

Medium 4.8 Published 12 Dec 2025 Updated 12 Dec 2025

A logged-in user can inject malicious scripts via stored XSS, allowing arbitrary code execution in other users' browsers.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Over the internet
Victim action needed: A user has to click or open something
Fix: None listed

What is CVE-2025-66284?

CVE-2025-66284 is a medium-severity cross-site scripting vulnerability in Japan Total System Co.,Ltd. GroupSession Free edition, published on 12 Dec 2025. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

Official description

Stored cross-site scripting vulnerabilities exist in GroupSession Free edition prior to ver5.7.1, GroupSession byCloud prior to ver5.7.1, and GroupSession ZION prior to ver5.7.1. A logged-in user can prepare a malicious page or URL, and an arbitrary script may be executed on the web browser when another user accesses it.

Weakness: CWE-79

Which versions are affected by CVE-2025-66284?

It affects 1 product.

Products include Groupsession Groupsession.

How do I fix CVE-2025-66284?

No fix has been published for CVE-2025-66284 yet. Limit exposure of the affected software until one is available.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2025-66284 being exploited?

There is no known exploitation of CVE-2025-66284 in the wild and no public exploit code.

Sources

Also known as GHSA-gvxm-fhfx-8g6r.