CVE-2021-31886: Siemens Apogee Modular Building Controller Firmware

Critical severity, CVSS 9.8. EPSS: 3% chance of exploitation in the next 30 days.

A vulnerability has been identified in APOGEE MBC (PPC) (BACnet) (All versions), APOGEE MBC (PPC) (P2 Ethernet) (All versions), APOGEE MEC (PPC) (BACnet) (All versions), APOGEE MEC (PPC) (P2 Ethernet) (All versions), APOGEE PXC Compact (BACnet) (All versions < V3.5.4), APOGEE PXC Compact (P2 Ethernet) (All versions < V2.8.19), APOGEE PXC Modular (BACnet) (All versions < V3.5.4), APOGEE PXC Modular (P2 Ethernet) (All versions < V2.8.19), Desigo PXC00-E.D (All versions >= V2.3 and < V6.30.016), Desigo PXC00-U (All versions >= V2.3 and < V6.30.016), Desigo PXC001-E.D (All versions >= V2.3 and < V6.30.016), Desigo PXC100-E.D (All versions >= V2.3 and < V6.30.016), Desigo PXC12-E.D (All versions >= V2.3 and < V6.30.016), Desigo PXC128-U (All versions >= V2.3 and < V6.30.016), Desigo PXC200-E.D (All versions >= V2.3 and < V6.30.016), Desigo PXC22-E.D (All versions >= V2.3 and < V6.30.016), Desigo PXC22.1-E.D (All versions >= V2.3 and < V6.30.016), Desigo PXC36.1-E.D (All versions >= V2.3 and < V6.30.016), Desigo PXC50-E.D (All versions >= V2.3 and < V6.30.016), Desigo PXC64-U (All versions >= V2.3 and < V6.30.016), Desigo PXM20-E (All versions >= V2.3 and < V6.30.016), Nucleus NET (All versions), Nucleus ReadyStart V3 (All versions < V2017.02.4), Nucleus Source Code (All versions), TALON TC Compact (BACnet) (All versions < V3.5.4), TALON TC Modular (BACnet) (All versions < V3.5.4). FTP server does not properly validate the length of the “USER” command, leading to stack-based buffer overflows. This may result in Denial-of-Service conditions and Remote Code Execution. (FSMD-2021-0010)

Affected products

Siemens Apogee Modular Building Controller Firmware: any version
Siemens Apogee Modular Equiment Controller Firmware: any version
Siemens Apogee Pxc Compact Firmware: before 2.8.19 (fixed in 2.8.19); before 3.5.4 (fixed in 3.5.4)
Siemens Apogee Pxc Modular Firmware: before 2.8.19 (fixed in 2.8.19); before 3.5.4 (fixed in 3.5.4)
Siemens Desigo PXC00-E.d Firmware: from 2.3, before 6.30.016 (fixed in 6.30.016)
Siemens Desigo PXC00-U Firmware: from 2.3, before 6.30.016 (fixed in 6.30.016)
Siemens Desigo PXC001-E.d Firmware: from 2.3, before 6.30.016 (fixed in 6.30.016)
Siemens Desigo PXC100-E.d Firmware: from 2.3, before 6.30.016 (fixed in 6.30.016)
Siemens Desigo PXC12-E.d Firmware: from 2.3, before 6.30.016 (fixed in 6.30.016)
Siemens Desigo PXC128-U Firmware: from 2.3, before 6.30.016 (fixed in 6.30.016)
Siemens Desigo PXC200-E.d Firmware: from 2.3, before 6.30.016 (fixed in 6.30.016)
Siemens Desigo PXC22-E.d Firmware: from 2.3, before 6.30.016 (fixed in 6.30.016)
Siemens Desigo PXC22.1-E.d Firmware: from 2.3, before 6.30.016 (fixed in 6.30.016)
Siemens Desigo PXC36.1-E.d Firmware: from 2.3, before 6.30.016 (fixed in 6.30.016)
Siemens Desigo PXC50-E.d Firmware: from 2.3, before 6.30.016 (fixed in 6.30.016)
Siemens Desigo PXC64-U Firmware: from 2.3, before 6.30.016 (fixed in 6.30.016)
Siemens Desigo PXM20-E Firmware: from 2.3, before 6.30.016 (fixed in 6.30.016)
Siemens Nucleus Net: any version
Siemens Nucleus Readystart v3: before 2017.02.4 (fixed in 2017.02.4)
Siemens Nucleus Source Code: any version
Siemens Talon Tc Compact Firmware: before 3.5.4 (fixed in 3.5.4)
Siemens Talon Tc Modular Firmware: before 3.5.4 (fixed in 3.5.4)

Published 2021-11-09. Last modified 2026-06-17.