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CVE-2021-31884

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

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), Capital VSTAR (All versions with enabled Ethernet options), 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). The DHCP client application assumes that the data supplied with the “Hostname” DHCP option is NULL terminated. In cases when global hostname variable is not defined, this may lead to Out-of-bound reads, writes, and Denial-of-service conditions.

(FSMD-2021-0014)

CRITICAL · CVSS 9.8 EPSS 0.01451
EPSS exploitation odds1.45% · top 29%
Schedule remediation
  • CVSS base score ≥ 7.0
No Sigma yet — build one → YARA rules0
Look this up elsewhere - one-click external pivots
NVDCVE.orgCISAExploit-DBGitHub PoCVulnCheck KEVGreyNoise
▸ How to read a CVE - triage first, then detect and patch
This page is every public fact about CVE-2021-31884, cross-linked. Its job is to answer one question fast - does this need my attention now? - and then hand you the two things you do about it. Here is how an analyst reads it.
Triage: should I act now? Four signals, and they are not interchangeable:
CVSSseverity - how bad it is IF exploited, 0-10. A high CVSS alone is not urgency; a flaw can be a perfect 10 and never actually be attacked. EPSSprobability - a model’s estimate of the chance it is exploited in the next 30 days, 0-1. This is the “will it actually happen” signal. CISA KEVconfirmed - it is being exploited in the wild right now. The strongest signal on the page; KEV beats any score. Weaponisedavailability - public exploits / PoCs, and especially Metasploit modules rated Excellent / Great. Reliable, packaged exploit code means low-skill attackers can use it today.
How they combine: KEV, or a dependable Metasploit module, means patch now regardless of CVSS. High CVSS + low EPSS + no exploit is real but not an emergency - schedule it. Low CVSS but KEV-listed still gets patched now. The verdict above already weighed these for you; this is how it got there.
Then what - two workflows:
Detectwhen you cannot patch today, follow this CVE to the ATT&CK techniques it enables, then Build a SIEM detection (the green button) - author a rule, test it in Atomic, deploy it. That buys visibility while the patch waits. PatchAffected products / packages tell you if you are exposed; Fixed versions by distribution and Vendor advisories give the exact version that closes it.
Reading order for the panels below: verdict + badges, then Public exploits / Metasploit (is it weaponised), then ATT&CK techniques + Sigma / IDS rules (can I detect it), then Affected products / packages + Fixed versions (am I exposed, what patches it), then Threat actors / IOCs (who uses it), then Scoring & timeline / references (the evidence).
↗

Exploitation momentum

496 days of EPSS
dormant
Flat and low - no real exploitation pressure. This reads the direction and speed of EPSS over time, which can move before EPSS itself peaks or before CISA lists it.
Window
▣

Severity & exploitation scoring

View on NVD →
CVSS base score
9.8
CRITICALCVSS v3.1 · [email protected]
EPSS exploitation probability
1.45%
Top 29%odds of exploitation in the next 30 days
CVSS metric silhouette
VectorComplexityPrivilegesInteractionScopeConfidentialityIntegrityAvailability
shape grows toward worst-case
SSVC triage
No SSVC vulnrichment for this CVE. CISA's Vulnrichment program scores newer CVEs (~2024 onwards) plus selected older critical ones. Use the EPSS probability + KEV status to triage instead.
CVSS vector breakdown
Exploitability - how they get in
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Impact - what breaks
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
VECTORCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Lifecycle
  1. 09 Nov 2021Published to NVD
  2. 17 Jun 2026Last modified
Every entry is a recorded date - NVD publish/modify, CISA KEV add, public exploit disclosure. No inferred events.
Attack path
Full kill chain
→
◆

ATT&CK techniques

1

Techniques this CVE enables. Pills with a solid outline are high confidence - named directly in ATT&CK or Nuclei, or human-curated by CTID; the rest are inferred from the weakness type using MITRE's CVE Mapping Methodology and the CWE → CAPEC chain. Broad, generic-weakness guesses are filtered out. A small N× marks a technique that N independent sources agree on.

T1190 · Exploit Public-Facing Application
▤ Build a SIEM detection for these techniques
⬡

Weakness Classification

CWE-170Improper Null Termination
▤

Affected Products & Versions

25
siemens capital vstarall versions
siemens nucleus netall versions
siemens nucleus readystart v3< 2017.02.1
siemens nucleus source codeall versions
siemens apogee modular building controller firmwareall versions
siemens apogee modular equiment controller firmwareall versions
siemens apogee pxc compact firmware< 2.8.19
siemens apogee pxc modular firmware< 2.8.19
siemens talon tc compact firmware< 3.5.4
siemens talon tc modular firmware< 3.5.4
siemens desigo pxc00-e.d firmware>= 2.3 and < 6.30.016
siemens desigo pxc00-u firmware>= 2.3 and < 6.30.016
siemens desigo pxc001-e.d firmware>= 2.3 and < 6.30.016
siemens desigo pxc12-e.d firmware>= 2.3 and < 6.30.016
siemens desigo pxc22-e.d firmware>= 2.3 and < 6.30.016
siemens desigo pxc22.1-e.d firmware>= 2.3 and < 6.30.016
siemens desigo pxc36.1-e.d firmware>= 2.3 and < 6.30.016
siemens desigo pxc50-e.d firmware>= 2.3 and < 6.30.016
siemens desigo pxc64-u firmware>= 2.3 and < 6.30.016
siemens desigo pxc100-e.d firmware>= 2.3 and < 6.30.016
siemens desigo pxc128-u firmware>= 2.3 and < 6.30.016
siemens desigo pxc200-e.d firmware>= 2.3 and < 6.30.016
siemens desigo pxm20-e firmware>= 2.3 and < 6.30.016
siemens apogee pxc compact firmware< 3.5.4
siemens apogee pxc modular firmware< 3.5.4
▤

Related CVEs

8
CVEs linked to this one by a shared weakness (CWE) or affected product - joins on data already in the engine, with the reason shown per row.
CVE-2019-8275 UltraVNC revision 1211 has multiple improper null termination vulnerabilities in... same CWE-170 CRITICAL CVE-2019-11044 In PHP versions 7.2.x below 7.2.26, 7.3.x below 7.3.13 and 7.4.0 on Windows, PHP... same CWE-170 LOW CVE-2019-11045 In PHP versions 7.2.x below 7.2.26, 7.3.x below 7.3.13 and 7.4.0, PHP DirectoryI... same CWE-170 LOW CVE-2020-7066 In PHP versions 7.2.x below 7.2.29, 7.3.x below 7.3.16 and 7.4.x below 7.4.4, wh... same CWE-170 MEDIUM CVE-2021-25663 A vulnerability has been identified in Capital Embedded AR Classic 431-422 (All ... same product HIGH CVE-2021-25664 A vulnerability has been identified in Capital Embedded AR Classic 431-422 (All ... same product HIGH CVE-2019-13939 A vulnerability has been identified in APOGEE MEC/MBC/PXC (P2) (All versions < V... same product HIGH CVE-2020-28388 A vulnerability has been identified in APOGEE PXC Compact (BACnet) (All versions... same product MEDIUM
⚑

Vendor Advisories

5
siemens-csafSSA-620288
siemens-csafSSA-114589
siemens-csafSSA-044112
cisa-csafcisa-csaf-csaf_files-OT-white-2021-icsa-21-313-03
cisa-csafcisa-csaf-csaf_files-OT-white-2021-icsa-21-315-07
🔗

References & Sources

3
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://cert-portal.siemens.com/productcert/pdf/ssa-044112.pdf
Vendor Advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-114589.pdf
Vendor Advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-620288.pdf
Vendor Advisory
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