HighCVE-2021-31888

    Siemens APOGEE MBC (PPC) (BACnet): Improper Null Termination (CVE-2021-31888)

    Published Sources: Siemens ProductCERT, CVE.org

    What is affected, what to do

    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), 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). FTP server does not properly validate the length of the “MKD/XMKD” command, leading to stack-based buffer overflows.

    Update nucleus_readystart_v3 to version 2017.02.4.

    Affected
    • Siemens APOGEE MBC (PPC) (BACnet) eq All versions..All versions
    • Siemens APOGEE MBC (PPC) (P2 Ethernet) eq All versions..All versions
    • Siemens APOGEE MEC (PPC) (BACnet) eq All versions..All versions
    • Siemens APOGEE MEC (PPC) (P2 Ethernet) eq All versions..All versions
    • Siemens APOGEE PXC Compact (BACnet) eq All versions < V3.5.4..All versions < V3.5.4
    • Siemens APOGEE PXC Compact (P2 Ethernet) eq All versions < V2.8.19..All versions < V2.8.19
    • Siemens APOGEE PXC Modular (BACnet) eq All versions < V3.5.4..All versions < V3.5.4
    • Siemens APOGEE PXC Modular (P2 Ethernet) eq All versions < V2.8.19..All versions < V2.8.19
    • Siemens Desigo PXC00-E.D eq All versions >= V2.3 and < V6.30.016..All versions >= V2.3 and < V6.30.016
    • Siemens Desigo PXC00-U eq All versions >= V2.3 and < V6.30.016..All versions >= V2.3 and < V6.30.016
    • Siemens Desigo PXC001-E.D eq All versions >= V2.3 and < V6.30.016..All versions >= V2.3 and < V6.30.016
    • Siemens Desigo PXC100-E.D eq All versions >= V2.3 and < V6.30.016..All versions >= V2.3 and < V6.30.016
    • Siemens Desigo PXC12-E.D eq All versions >= V2.3 and < V6.30.016..All versions >= V2.3 and < V6.30.016
    • Siemens Desigo PXC128-U eq All versions >= V2.3 and < V6.30.016..All versions >= V2.3 and < V6.30.016
    • Siemens Desigo PXC200-E.D eq All versions >= V2.3 and < V6.30.016..All versions >= V2.3 and < V6.30.016
    • Siemens Desigo PXC22-E.D eq All versions >= V2.3 and < V6.30.016..All versions >= V2.3 and < V6.30.016
    • Siemens Desigo PXC22.1-E.D eq All versions >= V2.3 and < V6.30.016..All versions >= V2.3 and < V6.30.016
    • Siemens Desigo PXC36.1-E.D eq All versions >= V2.3 and < V6.30.016..All versions >= V2.3 and < V6.30.016
    • Siemens Desigo PXC50-E.D eq All versions >= V2.3 and < V6.30.016..All versions >= V2.3 and < V6.30.016
    • Siemens Desigo PXC64-U eq All versions >= V2.3 and < V6.30.016..All versions >= V2.3 and < V6.30.016
    • Siemens Desigo PXM20-E eq All versions >= V2.3 and < V6.30.016..All versions >= V2.3 and < V6.30.016
    • Siemens Nucleus NET eq All versions..All versions
    • Siemens Nucleus ReadyStart V3 eq All versions < V2017.02.4..All versions < V2017.02.4
    • Siemens Nucleus Source Code eq All versions..All versions
    • Siemens TALON TC Compact (BACnet) eq All versions < V3.5.4..All versions < V3.5.4
    • Siemens TALON TC Modular (BACnet) eq All versions < V3.5.4..All versions < V3.5.4

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

    Metrics

    8.8

    Priority

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

    Source: NVD, CVSS v3

    8.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Siemens ProductCERT, CVE.org

    2.5 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 84.3

    Show all metrics
    Severity
    High
    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
    100.82 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
    8.8 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
    8.8
    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
    2.5 %
    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
    84.3
    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-170

    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 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), 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). FTP server does not properly validate the length of the “MKD/XMKD” command, leading to stack-based buffer overflows. This may result in Denial-of-Service conditions and Remote Code Execution. (FSMD-2021-0018)

    Source: siemens_advisory, 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 MBC (PPC) (BACnet)
    • All versions
    • —
    SiemensAPOGEE MBC (PPC) (P2 Ethernet)
    • All versions
    • —
    SiemensAPOGEE MEC (PPC) (BACnet)
    • All versions
    • —
    SiemensAPOGEE MEC (PPC) (P2 Ethernet)
    • All versions
    • —
    SiemensAPOGEE PXC Compact (BACnet)
    • All versions < V3.5.4
    • —
    SiemensAPOGEE PXC Compact (P2 Ethernet)
    • All versions < V2.8.19
    • —
    SiemensAPOGEE PXC Modular (BACnet)
    • All versions < V3.5.4
    • —
    SiemensAPOGEE PXC Modular (P2 Ethernet)
    • All versions < V2.8.19
    • —
    SiemensDesigo PXC00-E.D
    • All versions >= V2.3 and < V6.30.016
    • —
    SiemensDesigo PXC00-U
    • All versions >= V2.3 and < V6.30.016
    • —
    SiemensDesigo PXC001-E.D
    • All versions >= V2.3 and < V6.30.016
    • —
    SiemensDesigo PXC100-E.D
    • All versions >= V2.3 and < V6.30.016
    • —
    SiemensDesigo PXC12-E.D
    • All versions >= V2.3 and < V6.30.016
    • —
    SiemensDesigo PXC128-U
    • All versions >= V2.3 and < V6.30.016
    • —
    SiemensDesigo PXC200-E.D
    • All versions >= V2.3 and < V6.30.016
    • —
    SiemensDesigo PXC22-E.D
    • All versions >= V2.3 and < V6.30.016
    • —
    SiemensDesigo PXC22.1-E.D
    • All versions >= V2.3 and < V6.30.016
    • —
    SiemensDesigo PXC36.1-E.D
    • All versions >= V2.3 and < V6.30.016
    • —
    SiemensDesigo PXC50-E.D
    • All versions >= V2.3 and < V6.30.016
    • —
    SiemensDesigo PXC64-U
    • All versions >= V2.3 and < V6.30.016
    • —
    SiemensDesigo PXM20-E
    • All versions >= V2.3 and < V6.30.016
    • —
    SiemensNucleus NET
    • All versions
    • —
    SiemensNucleus ReadyStart V3
    • All versions < V2017.02.4
    • —
    SiemensNucleus Source Code
    • All versions
    • —
    SiemensTALON TC Compact (BACnet)
    • All versions < V3.5.4
    • —
    SiemensTALON TC Modular (BACnet)
    • All versions < V3.5.4
    • —
    siemensnucleus_net
    • —
    • —
    siemensnucleus_readystart_v3
    • < 2017.02.4
    • 2017.02.4
    siemensnucleus_source_code
    • —
    • —

    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—
    Othersiemensdesigo_pxc00-e.d_firmware—
    Othersiemensdesigo_pxc00-u_firmware—
    Othersiemensdesigo_pxc001-e.d_firmware—
    Othersiemensdesigo_pxc100-e.d_firmware—
    Othersiemensdesigo_pxc12-e.d_firmware—
    Othersiemensdesigo_pxc128-u_firmware—
    Othersiemensdesigo_pxc200-e.d_firmware—
    Othersiemensdesigo_pxc22-e.d_firmware—
    Othersiemensdesigo_pxc22.1-e.d_firmware—
    Othersiemensdesigo_pxc36.1-e.d_firmware—
    Othersiemensdesigo_pxc50-e.d_firmware—
    Othersiemensdesigo_pxc64-u_firmware—
    Othersiemensdesigo_pxm20-e_firmware—
    Othersiemenstalon_tc_compact_firmware—
    Othersiemenstalon_tc_modular_firmware—

    Weakness classes (CWE)

    • CWE-170Improper Null Termination

      Base

      The product does not terminate or incorrectly terminates a string or array with a null character or equivalent terminator.

      Entry at MITRE CWE-170

    References & sources

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    Badge preview for CVE-2021-31888
    <a href="https://intel.neosec.eu/en/cve/CVE-2021-31888"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-31888.svg?lang=en" alt="CVE-2021-31888 – NEOSEC Intel" height="20"></a>