CVE-2021-31886

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)

Published: 2021-11-09 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-31886 is rated High Risk (66.8/100): CVSS Critical severity, with medium exploitation likelihood (EPSS 1.85%). High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-31886

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-01 3.43% 1.85% -1.58%
2 2026-02-18 5.89% 3.43% -2.47%
3 2026-02-17 — 5.89% —

Full EPSS history (21 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-31886

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
7.5 2.0 HIGH
AV:N/AC:L/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 6.4 [email protected]

Weakness enumeration for CVE-2021-31886

Affected software / configurations for CVE-2021-31886

Vendor Product Version Raw CPE
siemens nucleus_net — cpe:2.3:a:siemens:nucleus_net:*:*:*:*:*:*:*:*
siemens nucleus_readystart_v3 < 2017.02.4 cpe:2.3:a:siemens:nucleus_readystart_v3:*:*:*:*:*:*:*:*
siemens nucleus_source_code — cpe:2.3:a:siemens:nucleus_source_code:*:*:*:*:*:*:*:*
siemens apogee_modular_building_controller_firmware — cpe:2.3:o:siemens:apogee_modular_building_controller_firmware:*:*:*:*:*:*:*:*
siemens apogee_modular_equiment_controller_firmware — cpe:2.3:o:siemens:apogee_modular_equiment_controller_firmware:*:*:*:*:*:*:*:*
siemens apogee_pxc_compact_firmware < 2.8.19 cpe:2.3:o:siemens:apogee_pxc_compact_firmware:*:*:*:*:p2_ethernet:*:*:*
siemens apogee_pxc_compact_firmware < 3.5.4 cpe:2.3:o:siemens:apogee_pxc_compact_firmware:*:*:*:*:bacnet:*:*:*
siemens apogee_pxc_modular_firmware < 2.8.19 cpe:2.3:o:siemens:apogee_pxc_modular_firmware:*:*:*:*:p2_ethernet:*:*:*
siemens apogee_pxc_modular_firmware < 3.5.4 cpe:2.3:o:siemens:apogee_pxc_modular_firmware:*:*:*:*:bacnet:*:*:*
siemens talon_tc_compact_firmware < 3.5.4 cpe:2.3:o:siemens:talon_tc_compact_firmware:*:*:*:*:*:*:*:*
siemens talon_tc_modular_firmware < 3.5.4 cpe:2.3:o:siemens:talon_tc_modular_firmware:*:*:*:*:*:*:*:*
siemens desigo_pxc00-e.d_firmware >= 2.3, < 6.30.016 cpe:2.3:o:siemens:desigo_pxc00-e.d_firmware:*:*:*:*:*:*:*:*
siemens desigo_pxc00-u_firmware >= 2.3, < 6.30.016 cpe:2.3:o:siemens:desigo_pxc00-u_firmware:*:*:*:*:*:*:*:*
siemens desigo_pxc001-e.d_firmware >= 2.3, < 6.30.016 cpe:2.3:o:siemens:desigo_pxc001-e.d_firmware:*:*:*:*:*:*:*:*
siemens desigo_pxc12-e.d_firmware >= 2.3, < 6.30.016 cpe:2.3:o:siemens:desigo_pxc12-e.d_firmware:*:*:*:*:*:*:*:*
siemens desigo_pxc22-e.d_firmware >= 2.3, < 6.30.016 cpe:2.3:o:siemens:desigo_pxc22-e.d_firmware:*:*:*:*:*:*:*:*
siemens desigo_pxc22.1-e.d_firmware >= 2.3, < 6.30.016 cpe:2.3:o:siemens:desigo_pxc22.1-e.d_firmware:*:*:*:*:*:*:*:*
siemens desigo_pxc36.1-e.d_firmware >= 2.3, < 6.30.016 cpe:2.3:o:siemens:desigo_pxc36.1-e.d_firmware:*:*:*:*:*:*:*:*
siemens desigo_pxc50-e.d_firmware >= 2.3, < 6.30.016 cpe:2.3:o:siemens:desigo_pxc50-e.d_firmware:*:*:*:*:*:*:*:*
siemens desigo_pxc64-u_firmware >= 2.3, < 6.30.016 cpe:2.3:o:siemens:desigo_pxc64-u_firmware:*:*:*:*:*:*:*:*
siemens desigo_pxc100-e.d_firmware >= 2.3, < 6.30.016 cpe:2.3:o:siemens:desigo_pxc100-e.d_firmware:*:*:*:*:*:*:*:*
siemens desigo_pxc128-u_firmware >= 2.3, < 6.30.016 cpe:2.3:o:siemens:desigo_pxc128-u_firmware:*:*:*:*:*:*:*:*
siemens desigo_pxc200-e.d_firmware >= 2.3, < 6.30.016 cpe:2.3:o:siemens:desigo_pxc200-e.d_firmware:*:*:*:*:*:*:*:*
siemens desigo_pxm20-e_firmware >= 2.3, < 6.30.016 cpe:2.3:o:siemens:desigo_pxm20-e_firmware:*:*:*:*:*:*:*:*

References for CVE-2021-31886

cvelogic Threat Intelligence