Home/CVE/A vulnerability has been identified in Capital Embedded AR Classic 431-422 (All versions), Capital Embedded AR Classic R
CVE
CVE-2021-256631
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), Nucleus NET (All versions), Nucleus ReadyStart V3 (All versions < V2017.02.4), Nucleus ReadyStart V4 (All versions < V4.1.0), Nucleus Source Code (All versions including affected IPv6 stack). The function that processes IPv6 headers does not check the lengths of extension header options, allowing attackers to put this function into an infinite loop with crafted length values.
HIGH · CVSS 7.5
EPSS 0.01885
EPSS exploitation odds1.88% · top 22%
Act now
- Public exploit or PoC is available
- CVSS base score ≥ 7.0
No Sigma yet — build one →
YARA rules0
Look this up elsewhere - one-click external pivots
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How to read a CVE - triage first, then detect and patch
This page is every public fact about CVE-2021-25663, 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 evidence
1 of 7 sources
Corroboration score 8/100 ·
emerging.
This counts how many independent sources have exploitation evidence, and separates two different things:
confirmed in-the-wild use (CISA KEV, Microsoft MSRC, ransomware activity) from
exploit / PoC availability (Metasploit, ExploitDB, Nuclei, public PoCs). A template or PoC existing means
an attack is possible and easy - it is not, on its own, proof the CVE is being exploited in the wild.
Exploit / PoC available
public PoC
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Exploitation momentum
490 days of EPSSdormant
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.
EPSS exploitation probability
1.88%
Top 22%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
VECTOR
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HLifecycle
- 22 Apr 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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Public Exploits & PoCs
1These PoC and exploit links come from public sources and are not verified to be safe or functional. Review the code before running anything, and treat unverified entries as untrusted. Signed-in users mark whether it works, rate 1-10, and can report malware with a required reason that becomes a public comment.
Source
Works?
no reports yet
Rating
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ATT&CK techniques
1Techniques 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.
▤ Build a SIEM detection for these techniques⬡
Weakness Classification
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Affected Products & Versions
5siemens capital vstarall versions
siemens nucleus netall versions
siemens nucleus readystart< 4.1.0
siemens nucleus source codeall versions
siemens nucleus readystart< 2017.02.4
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Related CVEs
8CVEs 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-2004-0748
mod_ssl in Apache 2.0.50 and earlier allows remote attackers to cause a denial o...
same CWE-835
CVE-2004-0753
The BMP image processor for (1) gdk-pixbuf before 0.22 and (2) gtk2 before 2.2.4...
same CWE-835
CVE-2005-0851
FileZilla FTP server before 0.9.6, when using MODE Z (zlib compression), allows ...
1
same CWE-835
CVE-2005-2224
aspnet_wp.exe in Microsoft ASP.NET web services allows remote attackers to cause...
same CWE-835
CVE-2021-25664
A vulnerability has been identified in Capital Embedded AR Classic 431-422 (All ...
same product
HIGH
CVE-2021-31884
A vulnerability has been identified in APOGEE MBC (PPC) (BACnet) (All versions),...
same product
CRITICAL
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
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Vendor Advisories
2siemens-csafSSA-248289
cisa-csafcisa-csaf-csaf_files-OT-white-2021-icsa-21-103-05
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References & Sources
3Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.