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Nucleus NetApplication · Siemens

CVE-2021-31887

HIGH · 8.8 CVSS v3.1 Published 2021-11-09
Fix available
A fix is available. Upgrade to 2.8.19 / 3.5.4 or later.
See remediation →
94/100
Remediation priority · Urgent
Remotely reachable Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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 “PWD/XPWD” command, leading to stack-based buffer overflows. This may result in Denial-of-Service conditions and Remote Code Execution. (FSMD-2021-0016)

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The FTP server component in affected Siemens building automation controllers (APOGEE, Desigo, Nucleus, TALON) fails to properly validate the length of the PWD/XPWD command argument, leading to a stack-based buffer overflow. An unauthenticated attacker sending a specially crafted PWD/XPWD command with excessive length can overwrite stack memory, potentially achieving remote code execution or causing denial of service.

MitigationApply available vendor firmware updates to the fixed versions specified (e.g., APOGEE PXC to V3.5.4/V2.8.19, Nucleus to V2017.02.4, Desigo to V6.30.016). For products with no patch available or where FTP is not operationally required, disable the FTP service and restrict network access to these devices.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Nucleus NetApplication
Affected:all versions
Nucleus Readystart V3Application
Affected:< 2017.02.4
Nucleus Source CodeApplication
Affected:all versions
Apogee Modular Building Controller FirmwareOperating system
Affected:all versions
Apogee Modular Equiment Controller FirmwareOperating system
Affected:all versions
Apogee Pxc Compact FirmwareOperating system
Affected:< 2.8.19< 3.5.4
Apogee Pxc Modular FirmwareOperating system
Affected:< 2.8.19< 3.5.4
Talon Tc Compact FirmwareOperating system
Affected:< 3.5.4

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the product model
    Locate the device model number on the physical device label or in the device's web interface or management console. Common models include APOGEE PXC (Compact or Modular), Modular Building Controller, Modular Equipment Controller, TALON TC Compact, or Nucleus-based devices.
    Affected if The model matches any of the following: APOGEE PXC Compact, APOGEE PXC Modular, APOGEE Modular Building Controller, APOGEE Modular Equipment Controller, TALON TC Compact, or any Nucleus-based device (Nucleus Net, Nucleus Readystart).
  2. Verify FTP service is enabled
    Check the device configuration through its management web interface, console, or network scan for open port 21 (FTP). Consult the device administration manual for the specific method to confirm FTP service status.
    Affected if FTP server is enabled and listening on the network. The vulnerability is not exploitable if FTP is disabled.
  3. Check firmware version against affected ranges
    Retrieve the installed firmware version from the device's web interface, management console, or via SNMP/management protocol as documented in the device manual. Compare the version number to the affected ranges.
    Affected if The firmware version is any of the following: Nucleus Readystart V3 older than 2017.02.4; APOGEE PXC Compact or Modular older than 2.8.19 or older than 3.5.4; TALON TC Compact older than 3.5.4; or any version of Nucleus Net, Nucleus Source Code, APOGEE Modular Building Controller, or APOGEE Modular
  4. Confirm device is network accessible
    Verify the device has an IP address and is reachable on the network. Determine if the FTP port (21/TCP) is exposed to the network or only accessible from a restricted management VLAN.
    Affected if The device FTP service is accessible from network segments where unauthenticated attackers could reach it. The flaw is exploitable remotely if FTP is exposed.

A user is affected if they have a vulnerable Nucleus or APOGEE/TALON device with FTP enabled, running a firmware version below the fixed releases (2017.02.4 for Nucleus, 2.8.19/3.5.4 for APOGEE PXC, 3.5.4 for TALON), and the FTP service is network-accessible.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 2.8.19 / 3.5.4 / 2017.02.4 or later
Fixed in 2.8.193.5.42017.02.4
Interim mitigation

Apply available vendor firmware updates to the fixed versions specified (e.g., APOGEE PXC to V3.5.4/V2.8.19, Nucleus to V2017.02.4, Desigo to V6.30.016). For products with no patch available or where FTP is not operationally required, disable the FTP service and restrict network access to these devices.

Recommended fix Moderate confidence

Nucleus ReadyStart V3: V2017.02.4; Apogee PXC Compact/Modular: V2.8.19 or V3.5.4 (depending on protocol); Talon TC: V3.5.4

  1. 1. Identify the specific product and firmware version in use from the affected product list.
  2. 2. For Nucleus ReadyStart V3: upgrade to version 2017.02.4 or later.
  3. 3. For Apogee PXC Compact (BACnet): upgrade to version 3.5.4 or later.
  4. 4. For Apogee PXC Compact (P2 Ethernet): upgrade to version 2.8.19 or later.
  5. 5. For Apogee PXC Modular (BACnet): upgrade to version 3.5.4 or later.
  6. 6. For Apogee PXC Modular (P2 Ethernet): upgrade to version 2.8.19 or later.
  7. 7. For Talon TC Compact (BACnet): upgrade to version 3.5.4 or later.
  8. 8. For Talon TC Modular (BACnet): upgrade to version 3.5.4 or later.
Caveat Verify compatibility with existing system integrations before upgrading; some legacy protocol support may change in newer versions

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Nucleus Net Scoped from the published advisory
  • Consultation12.0 h
  • Implementation20.0 h
  • Testing12.0 h
  • Review / QA8.0 h
52.0 hours of engineering $9,240
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-31887 in production — separate from our analysis above.

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What belongs here
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  • Version or environment caveats, and links to real fixes
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