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Fencer Vulns
critical 9.8

CVE-2021-31886 json

A vulnerability has been identified in APOGEE MBC (PPC) (BACnet) (All versions), APOGEE MBC (PPC) (P2 Ethernet) (All versions), APOGEE MEC…

published 2021-11-09 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-18761

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
3.1%
EPSS 3.1% chance of exploitation in 30 days, percentile 87%
public exploits
0
none known

Summary

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)

Patch / fix

  • siemens nucleus_readystart_v3 2017.02.4
  • siemens apogee_pxc_compact_firmware 2.8.19, 3.5.4
  • siemens apogee_pxc_modular_firmware 2.8.19, 3.5.4
  • siemens talon_tc_compact_firmware 3.5.4
  • siemens talon_tc_modular_firmware 3.5.4
  • siemens desigo_pxc00-e.d_firmware 6.30.016
  • siemens desigo_pxc00-u_firmware 6.30.016
  • siemens desigo_pxc001-e.d_firmware 6.30.016
  • siemens desigo_pxc12-e.d_firmware 6.30.016
  • siemens desigo_pxc22-e.d_firmware 6.30.016
  • siemens desigo_pxc22.1-e.d_firmware 6.30.016
  • siemens desigo_pxc36.1-e.d_firmware 6.30.016
  • siemens desigo_pxc50-e.d_firmware 6.30.016
  • siemens desigo_pxc64-u_firmware 6.30.016
  • siemens desigo_pxc100-e.d_firmware 6.30.016
  • siemens desigo_pxc128-u_firmware 6.30.016
  • siemens desigo_pxc200-e.d_firmware 6.30.016
  • siemens desigo_pxm20-e_firmware 6.30.016

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

cisa ICSA-21-313-03 updated cvss 9.8

Siemens Nucleus RTOS TCP/IP Stack

  • Siemens Nucleus NET
    affected: mitigation, no fix planned
  • Siemens Nucleus ReadyStart V3 <V2017.02.4
    affected: fixed in V2017.02.4 support.sw.siemens.com
  • Siemens Nucleus Source Code
    affected: vendor fix

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

cisa ICSA-21-315-07 updated cvss 9.8

Siemens Nucleus RTOS-based APOGEE and TALON Products (Update C)

  • Siemens APOGEE MBC (PPC) (BACnet) Siemens APOGEE MBC (PPC) (P2 Ethernet) Siemens APOGEE MEC (PPC) (BACnet) Siemens APOGEE MEC (PPC) (P2 Ethernet)
    affected: mitigation, no fix planned
  • Siemens APOGEE PXC Compact (BACnet) <V3.5.4
    affected: fixed in V3.5.4, mitigation
  • Siemens APOGEE PXC Compact (P2 Ethernet) <V2.8.19
    affected: fixed in V2.8.19, mitigation
  • Siemens APOGEE PXC Modular (BACnet) <V3.5.4
    affected: fixed in V3.5.4, mitigation
  • Siemens APOGEE PXC Modular (P2 Ethernet) <V2.8.19
    affected: fixed in V2.8.19, mitigation
  • Siemens Desigo PXC00-E.D >=V2.3_and_<V6.30.016 Siemens Desigo PXC00-U >=V2.3_and_<V6.30.016 Siemens Desigo PXC001-E.D >=V2.3_and_<V6.30.016 Siemens Desigo PXC12-E.D >=V2.3_and_<V6.30.016 Siemens Desigo PXC22-E.D >=V2.3_and_<V6.30.016 Siemens Desigo PXC22.1-E.D >=V2.3_and_<V6.30.016
    +7 more products
    Siemens Desigo PXC36.1-E.D >=V2.3_and_<V6.30.016 Siemens Desigo PXC50-E.D >=V2.3_and_<V6.30.016 Siemens Desigo PXC64-U >=V2.3_and_<V6.30.016 Siemens Desigo PXC100-E.D >=V2.3_and_<V6.30.016 Siemens Desigo PXC128-U >=V2.3_and_<V6.30.016 Siemens Desigo PXC200-E.D >=V2.3_and_<V6.30.016 Siemens Desigo PXM20-E >=V2.3_and_<V6.30.016
    affected: fixed in V6.30.016, mitigation support.industry.siemens.com
  • Siemens TALON TC Compact (BACnet) <V3.5.4 Siemens TALON TC Modular (BACnet) <V3.5.4
    affected: fixed in V3.5.4, mitigation

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

Exploit prediction

3.08% chance of exploitation in the next 30 days, higher than 87% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P

Affected products

  • Siemens APOGEE MBC (PPC) (BACnet)
  • Siemens APOGEE MBC (PPC) (P2 Ethernet)
  • Siemens APOGEE MEC (PPC) (BACnet)
  • Siemens APOGEE MEC (PPC) (P2 Ethernet)
  • Siemens APOGEE PXC Compact (BACnet)
  • Siemens APOGEE PXC Compact (P2 Ethernet)
  • Siemens APOGEE PXC Modular (BACnet)
  • Siemens APOGEE PXC Modular (P2 Ethernet)
  • Siemens Desigo PXC00-E.D
  • Siemens Desigo PXC00-U
  • Siemens Desigo PXC001-E.D
  • Siemens Desigo PXC100-E.D
  • Siemens Desigo PXC12-E.D
  • Siemens Desigo PXC128-U
  • Siemens Desigo PXC200-E.D
  • Siemens Desigo PXC22-E.D
  • Siemens Desigo PXC22.1-E.D
  • Siemens Desigo PXC36.1-E.D
  • Siemens Desigo PXC50-E.D
  • Siemens Desigo PXC64-U
  • Siemens Desigo PXM20-E
  • Siemens Nucleus NET
  • Siemens Nucleus ReadyStart V3
  • Siemens Nucleus Source Code
  • Siemens TALON TC Compact (BACnet)
  • Siemens TALON TC Modular (BACnet)

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.