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CVE-2025-66284

MEDIUM
4.8
CVSS Score
Published: December 12, 2025 at 05:01 AM UTC
Updated: October 7, 2026 at 08:10 PM UTC
2 products affected across 2 vendorsGroupsessionGroupSession

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Severity
MEDIUM4.8
Exploit prediction
EPSS 0.2%
SSVC
No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Groupsession· Groupsession
95%
v < 5.7.1
GroupSession· Japan Total System
60%
v < er5.7.1
Affected range stops below er5.7.1, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (2)

Vendor Advisory
Source: cverecord
https://groupsession.jp/info/info-news/security20251208
Third Party Advisory
Source: cverecord
https://jvn.jp/en/jp/JVN19940619/

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

4.8MEDIUMjpcert
Vector?

Quick Info

StatusANALYZED
CWE
CWE-79

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