CVE-2021-26566: Synology Diskstation Manager

Critical severity, CVSS 9.0. EPSS: 1.5% chance of exploitation in the next 30 days.

Insertion of sensitive information into sent data vulnerability in synorelayd in Synology DiskStation Manager (DSM) before 6.2.3-25426-3 allows man-in-the-middle attackers to execute arbitrary commands via inbound QuickConnect traffic.

Affected products

• Synology Diskstation Manager: before 6.2.3-25426-3 (fixed in 6.2.3-25426-3)
• Synology Diskstation Manager Unified Controller: version 3.0 only
• Synology Skynas Firmware: affected versions not specified
• Synology VS960HD Firmware: affected versions not specified

Published 2021-02-26. Last modified 2026-06-17.