CVE-2025-61987 is a vulnerability identified in the WebSocket implementation of Japan Total System Co.,Ltd.'s GroupSession collaboration products. The root cause is the absence of origin validation when establishing WebSocket connections. WebSockets are used for real-time communication, such as chat messaging, between clients and servers. Without origin validation, a malicious website can initiate a WebSocket connection to the GroupSession server using the victim's browser context. This allows the attacker to intercept or receive chat messages intended for the user, leading to unauthorized disclosure of potentially sensitive information. The affected products include GroupSession Free edition versions prior to 5.3.0, GroupSession byCloud prior to 5.3.3, and GroupSession ZION prior to 5.3.2. The vulnerability does not require any privileges or user interaction beyond visiting a crafted webpage, making it relatively easy to exploit remotely. The CVSS v3.0 score is 5.3 (medium severity), reflecting the network attack vector, low complexity, no privileges required, no user interaction, and limited impact confined to confidentiality loss. No integrity or availability impacts are noted. No public exploits have been reported yet, but the vulnerability's nature suggests potential for phishing or drive-by attacks to leak chat data. The fix involves implementing strict origin checks on WebSocket handshake requests to ensure connections originate only from trusted domains. This prevents malicious sites from hijacking WebSocket sessions and accessing chat information.

For European organizations, the primary impact is the potential unauthorized disclosure of sensitive chat communications within GroupSession collaboration environments. This could lead to leakage of confidential business discussions, personal data, or strategic information, undermining privacy and compliance with regulations such as GDPR. Although the vulnerability does not affect data integrity or system availability, the confidentiality breach could damage organizational reputation and result in regulatory penalties. Sectors relying heavily on secure internal communications, such as finance, healthcare, and government, are particularly at risk. Since exploitation requires only that a user visit a malicious webpage, attackers could leverage social engineering or phishing campaigns to target employees. The lack of authentication or user interaction requirements lowers the barrier for exploitation, increasing risk. However, the absence of known exploits in the wild and the medium CVSS score indicate that while the threat is credible, it is not currently widespread or critical. Organizations using affected GroupSession versions should prioritize patching to prevent potential data exposure.

1. Upgrade all affected GroupSession products to the fixed versions: Free edition to 5.3.0 or later, byCloud to 5.3.3 or later, and ZION to 5.3.2 or later, which include proper origin validation for WebSocket connections. 2. If immediate patching is not possible, implement network-level controls to restrict WebSocket connections to trusted origins and domains. 3. Employ Content Security Policy (CSP) headers to limit the sources from which scripts and connections can be initiated, reducing the risk of malicious page exploitation. 4. Educate users about the risks of visiting untrusted websites and phishing attacks that could exploit this vulnerability. 5. Monitor network traffic for unusual WebSocket connection attempts or unexpected data flows that could indicate exploitation attempts. 6. Conduct security assessments and penetration testing focusing on WebSocket implementations to identify similar weaknesses. 7. Review and enhance incident response plans to quickly address any detected data leakage incidents related to collaboration tools.