CVE-2025-54407 is a stored cross-site scripting vulnerability identified in Japan Total System Co., Ltd.'s GroupSession collaboration software, specifically affecting the Free edition prior to version 5.3.0, GroupSession byCloud prior to 5.3.3, and GroupSession ZION prior to 5.3.2. The vulnerability allows an attacker to inject malicious scripts into the application’s stored data, which are then executed in the context of a victim's browser when they access a crafted page or URL. This type of XSS can lead to session hijacking, credential theft, or unauthorized actions performed on behalf of the user. The vulnerability does not require any privileges (PR:N) but does require user interaction (UI:R) to trigger. The attack vector is network-based (AV:N), meaning exploitation can occur remotely over the internet. The CVSS 3.0 score of 6.1 reflects a medium severity, with partial impact on confidentiality and integrity but no impact on availability. The scope is changed (S:C), indicating the vulnerability affects resources beyond the vulnerable component, potentially impacting other users or systems. No known exploits have been reported in the wild yet, but the presence of stored XSS in collaboration software is concerning due to the potential for lateral movement and data exposure within organizations. The lack of official patch links suggests that users should monitor vendor communications closely for updates. The vulnerability highlights the importance of secure input handling and output encoding in web applications, especially those used for group collaboration and document sharing.

For European organizations, the exploitation of this stored XSS vulnerability could lead to unauthorized execution of scripts in users’ browsers, resulting in theft of session tokens, user credentials, or sensitive information accessible via the application. This could facilitate further attacks such as privilege escalation or lateral movement within the network. Given that GroupSession is a collaboration platform, compromised accounts could lead to exposure or manipulation of internal communications and documents, impacting confidentiality and integrity. Although availability is not directly affected, the reputational damage and potential regulatory consequences under GDPR for data breaches could be significant. Organizations relying on GroupSession Free edition or related products without timely patching are at risk. The medium severity suggests that while the vulnerability is not critical, it still poses a meaningful threat, especially in environments with high user interaction and sensitive data. The absence of known exploits reduces immediate risk but does not eliminate the threat, as attackers may develop exploits once the vulnerability is public. European entities with remote or hybrid workforces using this software are particularly vulnerable due to increased reliance on web-based collaboration tools.

1. Immediately upgrade affected GroupSession products to versions 5.3.0 or later for Free edition, 5.3.3 or later for byCloud, and 5.3.2 or later for ZION once patches are available. 2. Until patches are applied, implement strict input validation and output encoding on all user-supplied data to prevent script injection. 3. Deploy Content Security Policies (CSP) to restrict the execution of unauthorized scripts in browsers. 4. Educate users to avoid clicking on suspicious or untrusted links related to GroupSession environments. 5. Monitor logs and user activity for unusual behavior that may indicate exploitation attempts. 6. Consider using web application firewalls (WAFs) with rules tailored to detect and block XSS payloads targeting GroupSession. 7. Regularly review and update security configurations of collaboration platforms to minimize attack surface. 8. Coordinate with the vendor for timely security advisories and patch releases. 9. Conduct security awareness training emphasizing risks of XSS and safe browsing practices. 10. Implement multi-factor authentication (MFA) to reduce impact if credentials are compromised via XSS.