CVE-2021-25677: Siemens Nucleus Net

Medium severity, CVSS 5.3. EPSS: 1.1% chance of exploitation in the next 30 days.

A vulnerability has been identified in APOGEE PXC Compact (BACnet) (All versions < V3.5.5), APOGEE PXC Compact (P2 Ethernet) (All versions < V2.8.20), APOGEE PXC Modular (BACnet) (All versions < V3.5.5), APOGEE PXC Modular (P2 Ethernet) (All versions < V2.8.20), Nucleus NET (All versions), Nucleus ReadyStart V3 (All versions < V2017.02.3), Nucleus ReadyStart V3 (All versions < V2017.02.4), Nucleus ReadyStart V4 (All versions < V4.1.0), Nucleus Source Code (Versions including affected DNS modules), SIMOTICS CONNECT 400 (All versions < V0.5.0.0), SIMOTICS CONNECT 400 (All versions >= V0.5.0.0 < V1.0.0.0), TALON TC Compact (BACnet) (All versions < V3.5.5), TALON TC Modular (BACnet) (All versions < V3.5.5). The DNS client does not properly randomize DNS transaction IDs. That could allow an attacker to poison the DNS cache or spoof DNS resolving.

Affected products

• Siemens Nucleus Net: any version
• Siemens Nucleus Readystart v3: before 2017.02.4 (fixed in 2017.02.4)
• Siemens Nucleus Readystart v4: before 4.1.0 (fixed in 4.1.0)
• Siemens Nucleus Source Code: affected versions not specified
• Siemens Simotics Connect 400 Firmware: from 0.5.0.0

Published 2021-04-22. Last modified 2026-06-17.