How severe is CVE-2021-31887?

CVE-2021-31887 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-31887 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (82nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-31887?

CVE-2021-31887 primarily affects Siemens Nucleus Net. In total, 24 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-31887?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-31887 published?

CVE-2021-31887 was published on 2021-11-09 and last updated on 2026-06-17.

CVE-2021-31887

CVE-2021-31887 is a high-severity vulnerability in Siemens Nucleus Net with a CVSS 3.x base score of 8.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-170.

Key facts

Severity: High (CVSS 3.x base score 8.8)
CVSS v2: 6.5
EPSS exploit prediction: 2% (82nd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-170
Affected product: Siemens Nucleus Net
Published: 2021-11-09
Last modified: 2026-06-17

Description

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 “PWD/XPWD” command, leading to stack-based buffer overflows. This may result in Denial-of-Service conditions and Remote Code Execution. (FSMD-2021-0016)

Frequently asked questions

What is CVE-2021-31887?: 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 “PWD/XPWD” command, leading to stack-based buffer overflows. This may result in Denial-of-Service conditions and Remote Code Execution. (FSMD-2021-0016)
How severe is CVE-2021-31887?: CVE-2021-31887 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-31887 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (82nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-31887?: CVE-2021-31887 primarily affects Siemens Nucleus Net. In total, 24 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-31887?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-31887 published?: CVE-2021-31887 was published on 2021-11-09 and last updated on 2026-06-17.

References

Affected products (24)

cpe:2.3:a:siemens:nucleus_net:*:*:*:*:*:*:*:*
cpe:2.3:a:siemens:nucleus_readystart_v3:*:*:*:*:*:*:*:*
cpe:2.3:a:siemens:nucleus_source_code:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:apogee_modular_building_controller_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:apogee_modular_equiment_controller_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:apogee_pxc_compact_firmware:*:*:*:*:p2_ethernet:*:*:*
cpe:2.3:o:siemens:apogee_pxc_compact_firmware:*:*:*:*:bacnet:*:*:*
cpe:2.3:o:siemens:apogee_pxc_modular_firmware:*:*:*:*:p2_ethernet:*:*:*
cpe:2.3:o:siemens:apogee_pxc_modular_firmware:*:*:*:*:bacnet:*:*:*
cpe:2.3:o:siemens:talon_tc_compact_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:talon_tc_modular_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:desigo_pxc00-e.d_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:desigo_pxc00-u_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:desigo_pxc001-e.d_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:desigo_pxc12-e.d_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:desigo_pxc22-e.d_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:desigo_pxc22.1-e.d_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:desigo_pxc36.1-e.d_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:desigo_pxc50-e.d_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:desigo_pxc64-u_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:desigo_pxc100-e.d_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:desigo_pxc128-u_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:desigo_pxc200-e.d_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:desigo_pxm20-e_firmware:*:*:*:*:*:*:*:*

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