CVE-2021-47960: Information Disclosure in Synology SSL VPN Client

The primary impact of CVE-2021-47960 is the potential for sensitive information disclosure. Successful exploitation allows an attacker to retrieve files from the Synology SSL VPN Client's installation directory. This could include configuration files containing credentials or connection details, SSL certificates used for encryption, and log files that might reveal user activity or system behavior. The attacker leverages user interaction with a crafted web page, suggesting a social engineering component may be involved. While the vulnerability is bound to the loopback interface, the ability to extract sensitive data represents a significant risk, potentially enabling further attacks or unauthorized access to the network.

1. Reserved2026-04-10
2. Published2026-04-10
3. EPSS updated2026-04-17

The primary mitigation for CVE-2021-47960 is to upgrade Synology SSL VPN Client to version 1.4.5-0684 or later. If upgrading is not immediately feasible, consider implementing network segmentation to restrict access to the SSL VPN Client's installation directory. Review web application firewall (WAF) rules to detect and block malicious requests targeting the vulnerable endpoint. Monitor system logs for unusual file access patterns or suspicious activity. After upgrading, verify the fix by attempting to access the vulnerable files via a web browser; access should be denied.