CVE-2025-58576 is a Cross-Site Request Forgery (CSRF) vulnerability identified in Japan Total System Co., Ltd.'s GroupSession collaboration software products, specifically the Free edition prior to version 5.3.0, byCloud prior to 5.3.3, and ZION prior to 5.3.2. CSRF vulnerabilities occur when an attacker tricks an authenticated user into submitting unwanted requests to a web application in which they are logged in, thereby causing the application to perform actions without the user's consent. In this case, if a user who is logged into GroupSession accesses a maliciously crafted webpage, the attacker can induce the user’s browser to send unauthorized commands to the GroupSession server. This can lead to unintended operations such as modifying data or changing settings, impacting the integrity of the system. The vulnerability does not affect confidentiality or availability directly and does not require the attacker to have any privileges or prior authentication, but it does require the victim to interact with a malicious link or page (user interaction). The CVSS 3.0 base score is 4.3 (medium severity), reflecting the network attack vector, low attack complexity, no privileges required, but requiring user interaction and impacting integrity only. No public exploits or active exploitation have been reported to date. The vulnerability was published on December 12, 2025, and users are advised to upgrade to the fixed versions 5.3.0 or later for Free edition, 5.3.3 or later for byCloud, and 5.3.2 or later for ZION to remediate the issue.

For European organizations using affected versions of GroupSession, this vulnerability poses a risk of unauthorized modification of data or settings within the collaboration platform if users are tricked into visiting malicious websites. This can lead to data integrity issues, potential disruption of workflows, and unauthorized changes that may affect business operations. While the vulnerability does not expose sensitive data directly or cause denial of service, the integrity impact can undermine trust in the system and may facilitate further attacks if combined with other vulnerabilities. Organizations with users who frequently access external web content or have less stringent browser security policies are at higher risk. The impact is particularly relevant for sectors relying on GroupSession for internal communication and document management, such as government agencies, educational institutions, and enterprises across Europe. Failure to patch could also increase the attack surface for threat actors targeting European entities using this software.

European organizations should immediately upgrade all affected GroupSession installations to the patched versions: 5.3.0 or later for Free edition, 5.3.3 or later for byCloud, and 5.3.2 or later for ZION. Until patches are applied, implement strict Content Security Policy (CSP) headers to restrict the execution of untrusted scripts and reduce the risk of CSRF attacks. Additionally, enable or enforce anti-CSRF tokens in all forms and state-changing requests within the application if configurable. Educate users about the risks of clicking on suspicious links or visiting untrusted websites while logged into GroupSession. Network-level controls such as web filtering to block known malicious domains and monitoring for unusual application behavior can provide additional layers of defense. Regularly audit and review user permissions within GroupSession to minimize potential damage from unauthorized actions. Finally, maintain up-to-date backups of critical data to recover from any unintended changes caused by exploitation attempts.