MediumCVE-2020-28388

    Siemens APOGEE PXC Compact (BACnet): Predictable Exact Value from Previous Values (CVE-2020-28388)

    Published Sources: CVE.org

    What is affected, what to do

    A vulnerability has been identified in APOGEE PXC Compact (BACnet) (All versions < V3.5.5), APOGEE PXC Compact (P2 Ethernet) (All versions < V2.8.20), APOGEE PXC Modular (BACnet) (All versions < V3.5.5), APOGEE PXC Modular (P2 Ethernet) (All versions < V2.8.20), Nucleus NET (All versions < V5.2), Nucleus ReadyStart V3 (All versions < V2012.12), Nucleus Source Code (All versions), PLUSCONTROL 1st Gen (All versions), TALON TC Compact (BACnet) (All versions < V3.5.5), TALON TC Modular (BACnet) (All versions < V3.5.5). Initial Sequence Numbers (ISNs) for TCP connections are derived from an insufficiently random source.

    Update nucleus_net to version 5.2, nucleus_readystart to version 2012.12.

    Affected
    • Siemens APOGEE PXC Compact (BACnet) eq All versions < V3.5.5..All versions < V3.5.5
    • Siemens APOGEE PXC Compact (P2 Ethernet) eq All versions < V2.8.20..All versions < V2.8.20
    • Siemens APOGEE PXC Modular (BACnet) eq All versions < V3.5.5..All versions < V3.5.5
    • Siemens APOGEE PXC Modular (P2 Ethernet) eq All versions < V2.8.20..All versions < V2.8.20
    • Siemens Nucleus NET eq All versions < V5.2..All versions < V5.2
    • Siemens Nucleus ReadyStart V3 eq All versions < V2012.12..All versions < V2012.12
    • Siemens Nucleus Source Code eq All versions..All versions
    • Siemens PLUSCONTROL 1st Gen eq All versions..All versions
    • Siemens TALON TC Compact (BACnet) eq All versions < V3.5.5..All versions < V3.5.5
    • Siemens TALON TC Modular (BACnet) eq All versions < V3.5.5..All versions < V3.5.5

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    Metrics

    6.5

    Priority

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

    Source: Vendor (CNA), CVSS v3

    6.5

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: CVE.org

    1.4 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 71.4

    Show all metrics
    Severity
    Medium
    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
    73.28 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
    6.5 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
    6.5
    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“.

    Read in glossary
    1.4 %
    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
    71.4
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    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
    CISA assessment (SSVC)
    Exploitation: none known · automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 2 June 2026
    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-342

    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
    Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
    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 APOGEE PXC Compact (BACnet) (All versions < V3.5.5), APOGEE PXC Compact (P2 Ethernet) (All versions < V2.8.20), APOGEE PXC Modular (BACnet) (All versions < V3.5.5), APOGEE PXC Modular (P2 Ethernet) (All versions < V2.8.20), Nucleus NET (All versions < V5.2), Nucleus ReadyStart V3 (All versions < V2012.12), Nucleus Source Code (All versions), PLUSCONTROL 1st Gen (All versions), TALON TC Compact (BACnet) (All versions < V3.5.5), TALON TC Modular (BACnet) (All versions < V3.5.5). Initial Sequence Numbers (ISNs) for TCP connections are derived from an insufficiently random source. As a result, the ISN of current and future TCP connections could be predictable. An attacker could hijack existing sessions or spoof future ones.

    Source: 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
    SiemensAPOGEE PXC Compact (BACnet)
    • All versions < V3.5.5
    • —
    SiemensAPOGEE PXC Compact (P2 Ethernet)
    • All versions < V2.8.20
    • —
    SiemensAPOGEE PXC Modular (BACnet)
    • All versions < V3.5.5
    • —
    SiemensAPOGEE PXC Modular (P2 Ethernet)
    • All versions < V2.8.20
    • —
    SiemensNucleus NET
    • All versions < V5.2
    • —
    SiemensNucleus ReadyStart V3
    • All versions < V2012.12
    • —
    SiemensNucleus Source Code
    • All versions
    • —
    SiemensPLUSCONTROL 1st Gen
    • All versions
    • —
    SiemensTALON TC Compact (BACnet)
    • All versions < V3.5.5
    • —
    SiemensTALON TC Modular (BACnet)
    • All versions < V3.5.5
    • —
    siemenscapital_vstar
    • —
    • —
    siemensnucleus_net
    • < 5.2
    • 5.2
    siemensnucleus_readystart
    • < 2012.12
    • 2012.12
    siemensnucleus_source_code
    • —
    • —
    siemenspluscontrol_1st_gen
    • —
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-342Predictable Exact Value from Previous Values

      Base

      An exact value or random number can be precisely predicted by observing previous values.

      Entry at MITRE CWE-342

    References & sources

    Linked advisories

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    Badge preview for CVE-2020-28388
    <a href="https://intel.neosec.eu/en/cve/CVE-2020-28388"><img src="https://intel.neosec.eu/badge/cve/CVE-2020-28388.svg?lang=en" alt="CVE-2020-28388 – NEOSEC Intel" height="20"></a>