CVE-2021-31881

Home/CVE/A vulnerability has been identified in Capital Embedded AR Classic 431-422 (All versions), Capital Embedded AR Classic R

CVE

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A vulnerability has been identified in Capital Embedded AR Classic 431-422 (All versions), Capital Embedded AR Classic R

A vulnerability has been identified in Capital Embedded AR Classic 431-422 (All versions), Capital Embedded AR Classic R20-11 (All versions < V2303). When processing a DHCP OFFER message, the DHCP client application does not validate the length of the Vendor option(s), leading to Denial-of-Service conditions. (FSMD-2021-0008)

HIGH · CVSS 7.1 EPSS 0.01477

EPSS exploitation odds1.48% · top 28%

Schedule remediation

CVSS base score ≥ 7.0

No Sigma yet — build one → YARA rules0

Look this up elsewhere - one-click external pivots

NVD CVE.org CISA Exploit-DB GitHub PoC VulnCheck KEV GreyNoise

▸ How to read a CVE - triage first, then detect and patch

This page is every public fact about CVE-2021-31881, 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).

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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

EPSS 0.009 → 0.015 peak 0.015 velocity -0.000

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Severity & exploitation scoring

View on NVD →

CVSS base score

7.1

HIGHCVSS v3.1 · [email protected]

EPSS exploitation probability

1.48%

Top 28%odds of exploitation in the next 30 days

CVSS metric silhouette

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:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

Lifecycle

09 Nov 2021Published to NVD
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

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ATT&CK techniques

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.

T1210 · Exploitation of Remote Services

▤ Build a SIEM detection for these techniques

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CAPEC attack patterns

Attack patterns this CVE enables - the bridge from weakness to ATT&CK technique.

CAPEC-CAPEC-540 · Overread Buffers

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Weakness Classification

CWE-125Out-of-bounds Read

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Affected Products & Versions

siemens capital vstarall versions
siemens nucleus netall versions
siemens nucleus readystart v3< 2012.08
siemens nucleus source codeall versions
siemens apogee modular building controller firmwareall versions
siemens apogee modular equiment controller firmwareall versions
siemens apogee pxc compact firmwareall versions
siemens apogee pxc modular firmwareall versions
siemens talon tc compact firmwareall versions
siemens talon tc modular firmwareall versions

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Related CVEs

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-1999-0022 Local user gains root privileges via buffer overflow in rdist, via expstr() func... same CWE-125 HIGH CVE-1999-0029 root privileges via buffer overflow in ordist command on SGI IRIX systems. 1 same CWE-125 HIGH CVE-1999-0006 Buffer overflow in POP servers based on BSD/Qualcomm's qpopper allows remote att... 2 same CWE-125 CRITICAL CVE-2004-0183 TCPDUMP 3.8.1 and earlier allows remote attackers to cause a denial of service (... same CWE-125 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 CVE-2021-31344 A vulnerability has been identified in Capital Embedded AR Classic 431-422 (All ... same product MEDIUM CVE-2021-31345 A vulnerability has been identified in Capital Embedded AR Classic 431-422 (All ... same product HIGH

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Vendor Advisories

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
cisa-csafcisa-csaf-csaf_files-OT-white-2021-icsa-21-350-06