CriticalCVE-2021-31890

    Siemens Capital Embedded AR Classic 431-422: Improper Handling of Inconsistent Structural Elements (CVE-2021-31890)

    Published Sources: Siemens ProductCERT, OSV, CVE.org

    What is affected, what to do

    A vulnerability has been identified in Capital Embedded AR Classic 431-422 (All versions), Capital Embedded AR Classic R20-11 (All versions < V2303), PLUSCONTROL 1st Gen (All versions), SIMOTICS CONNECT 400 (All versions < V0.5.0.0), SIMOTICS CONNECT 400 (All versions < V1.0.0.0). The total length of an TCP payload (set in the IP header) is unchecked.

    Update nucleus_readystart_v3 to version 2017.02.4, nucleus_readystart_v4 to version 4.1.1, :unknown: to version SoCVersion:2022-01-05.

    Affected
    • Siemens PLUSCONTROL 1st Gen eq All versions..All versions
    • Siemens SIMOTICS CONNECT 400 eq All versions < V0.5.0.0..All versions < V0.5.0.0
    • Siemens SIMOTICS CONNECT 400 eq All versions < V1.0.0.0..All versions < V1.0.0.0

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    9.1

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Siemens ProductCERT, OSV, CVE.org

    2.2 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 82.6

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    92.11 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    9.1 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.5
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

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    2.2 %
    Moderate — model estimates 1-10% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    82.6
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-240

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    A vulnerability has been identified in Capital Embedded AR Classic 431-422 (All versions), Capital Embedded AR Classic R20-11 (All versions < V2303), PLUSCONTROL 1st Gen (All versions), SIMOTICS CONNECT 400 (All versions < V0.5.0.0), SIMOTICS CONNECT 400 (All versions < V1.0.0.0). The total length of an TCP payload (set in the IP header) is unchecked. This may lead to various side effects, including Information Leak and Denial-of-Service conditions, depending on the network buffer organization in memory. (FSMD-2021-0017)

    Source: siemens_advisory, OSV (Open Source Vulnerabilities), NVD (NIST), cvelistv5

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    SiemensCapital Embedded AR Classic 431-422
    • —
    • —
    SiemensCapital Embedded AR Classic R20-11
    • —
    • —
    SiemensPLUSCONTROL 1st Gen
    • All versions
    • —
    SiemensSIMOTICS CONNECT 400
    • All versions < V0.5.0.0
    • All versions < V1.0.0.0
    • —
    • —
    siemenscapital_vstar
    • —
    • —
    siemensnucleus_net
    • —
    • —
    siemensnucleus_readystart_v3
    • < 2017.02.4
    • 2017.02.4
    siemensnucleus_readystart_v4
    • < 4.1.1
    • 4.1.1
    siemensnucleus_source_code
    • —
    • —
    android:unknown:
    • SoCVersion
    • SoCVersion:0
    • —
    • SoCVersion:2022-01-05

    Vendors and products

    Affected operating systems

    Affected operating systems
    Othersiemensapogee_modular_building_controller_firmware—
    Othersiemensapogee_modular_equiment_controller_firmware—
    Othersiemensapogee_pxc_compact_firmware—
    Othersiemensapogee_pxc_modular_firmware—
    Othersiemenstalon_tc_compact_firmware—
    Othersiemenstalon_tc_modular_firmware—

    Weakness classes (CWE)

    • CWE-240Improper Handling of Inconsistent Structural Elements

      Base

      The product does not handle or incorrectly handles when two or more structural elements should be consistent, but are not.

      Entry at MITRE CWE-240

    References & sources

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    <a href="https://intel.neosec.eu/en/cve/CVE-2021-31890"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-31890.svg?lang=en" alt="CVE-2021-31890 – NEOSEC Intel" height="20"></a>