CVE-2025-66284Network attack vector

Authenticated stored script execution in victim browsers

Published Dec 12, 2025 · Updated Dec 12, 2025

Stored cross-site scripting in GroupSession editions before 5.7.1 allows remote authenticated users to run scripts in another user's browser. The vendor has not disclosed the affected feature, input field, storage path, or missing output-encoding operation because those details could enable attacks. Exploitation requires a logged-in attacker to prepare malicious content and another user to open the crafted page or URL, exposing that browser context to script-driven reading or modification.

CVSS severity4.8
Medium
EPSS probability0.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored cross-site scripting in GroupSession editions before 5.7.1 allows remote authenticated users to run scripts in another user's browser. The vendor has not disclosed the affected feature, input field, storage path, or missing output-encoding operation because those details could enable attacks. Exploitation requires a logged-in attacker to prepare malicious content and another user to open the crafted page or URL, exposing that browser context to script-driven reading or modification.

The record

CVE
CVE-2025-66284
Published
Dec 12, 2025
Updated
Dec 12, 2025
Vendor
Japan Total System Co.,Ltd.
Product
GroupSession ZION
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 12, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 12, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=prior to ver5.7.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Japan Total System Co.,Ltd. · GroupSession ZIONversion=prior to ver5.7.1
Japan Total System Co.,Ltd. · GroupSession byCloudversion=prior to ver5.7.1
Japan Total System Co.,Ltd. · GroupSession Free editionversion=prior to ver5.7.1

Published CVSS scores

4.8JPCERT/CCCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
5.4JPCERT/CCCVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007JavaScript/JScript

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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