VulnerabilityPublished 12 Dec 2025

CVE-2025-66284: Japan Total System GroupSession Free edition · Cross-site Scripting (XSS)

Affects Japan Total System GroupSession Free editionSource CVE Database V5

Not known to be exploited · CVSS 5.4 Medium : upgrade to 5.7.1 when convenient.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 3.0 base score

5.4Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.1% chance of exploitation in 30 days – higher than 6% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 5.7.1

CVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: Required
Scope: Changed
Confidentiality: Low
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 12 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade Japan Total System GroupSession Free edition to 5.7.1.

Affected software

Product	Affected	Fixed in
Japan Total System Co.,Ltd. GroupSession Free edition	Affected <5.7.1	Fixed in 5.7.1

AI-suggested

Upgrade all affected GroupSession products to version 5.7.1 or later immediately to apply the official patch addressing this XSS vulnerability.
Implement strict input validation and output encoding on all user-supplied data to prevent injection of malicious scripts.
Deploy Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers.
Conduct user awareness training to reduce the risk of users clicking on suspicious links or pages within the application.
Monitor application logs and user activity for unusual behavior indicative of exploitation attempts.
Where possible, restrict privileges of users to the minimum necessary to reduce the risk posed by authenticated attackers.
Consider implementing web application firewalls (WAF) with rules to detect and block XSS attack patterns targeting GroupSession endpoints.
Regularly review and update security configurations and perform security testing to detect similar vulnerabilities proactively.

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.

Impact

For European organizations using GroupSession products, this vulnerability poses a risk to the confidentiality and integrity of user data and sessions. Exploitation could allow attackers to steal session cookies, enabling impersonation of legitimate users, or execute unauthorized actions within the application context. This could lead to data leakage, unauthorized access to sensitive information, and potential lateral movement within the network if GroupSession is integrated with other internal systems. Although availability is not directly impacted, the indirect consequences of compromised accounts could disrupt business operations. The requirement for authenticated access and user interaction limits the attack surface but does not eliminate risk, especially in environments with many users or where social engineering could be employed. Organizations handling sensitive or regulated data (e.g., GDPR-protected personal data) must consider the compliance implications of such a vulnerability.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 19 Dec 2025, 08:33 UTC

Technical details

References

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