dbcve.org
Capital VstarApplication · Siemens

CVE-2021-31889

CRITICAL · 9.1 CVSS v3.1 Published 2021-11-09
Fix available
A fix is available. Upgrade to 2017.02.3 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges 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 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). Malformed TCP packets with a corrupted SACK option leads to Information Leaks and Denial-of-Service conditions. (FSMD-2021-0015)

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

A vulnerability in the TCP stack of Siemens Capital Embedded AR Classic, PLUSCONTROL, and SIMOTICS CONNECT 400 devices allows malformed TCP packets with corrupted SACK (Selective Acknowledgment) options to trigger information leaks and denial-of-service conditions. The vulnerability stems from improper handling of malformed TCP options during packet processing.

MitigationApply vendor-provided patches (V2303 or later for Capital Embedded AR Classic R20-11, V0.5.0.0 or later for SIMOTICS CONNECT 400). For unpatchable versions (Capital Embedded AR Classic 431-422, PLUSCONTROL 1st Gen), implement network segmentation and firewall rules to filter malformed TCP packets at network boundaries.

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
Capital VstarApplication
Affected:all versions
Nucleus NetApplication
Affected:all versions
Nucleus Readystart V3Application
Affected:< 2017.02.3
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:all versions
Apogee Pxc Modular FirmwareOperating system
Affected:all versions

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
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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 installed Siemens product
    Determine if the system runs Capital Embedded AR Classic, PLUSCONTROL, SIMOTICS CONNECT 400, or any Apogee controller (Modular Building Controller, Modular Equiment Controller, PXC Compact, or PXC Modular). Check the device firmware, software inventory, or system information.
    Affected if The product is any of: Siemens Capital Vstar, Siemens Nucleus Net, Siemens Nucleus Readystart V3, Siemens Nucleus Source Code, or any Apogee controller firmware.
  2. Check the software or firmware version
    Retrieve the installed version of the Capital software, Nucleus components, or Apogee controller firmware. For Capital: check the About or version info in the software. For SIMOTICS CONNECT 400: check the device firmware version via web interface or CLI. For Apogee: check the firmware version through the building management system or device console.
    Affected if Version is any for Vstar, Nucleus Net, Nucleus Source Code, or Apogee firmwares; or Nucleus Readystart V3 is before 2017.02.3.
  3. Confirm TCP/IP networking is enabled
    Verify that the device has TCP/IP stack active and network interfaces are configured. Check if the device is connected to an IP network and can process TCP traffic. On Capital: verify network adapters are enabled. On SIMOTICS CONNECT 400: check network settings. On Apogee: verify IP configuration in the BMS.
    Affected if TCP/IP networking is enabled and the device can accept TCP connections.
  4. Assess network exposure
    Determine if the device is reachable from network segments outside trusted internal networks. Check firewall rules, VLAN configuration, and access control lists. Identify if the device TCP ports are exposed to untrusted networks or the internet.
    Affected if The device TCP stack is accessible from network segments that cannot be trusted to filter malformed TCP packets.

The environment is affected if it runs any of the listed Siemens products with the TCP stack enabled and the version falls within or outside (for Nucleus Readystart V3) the specified ranges, especially if the device 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.

From vendor data
Upgrade available Upgrade to 2017.02.3 or later
Fixed in 2017.02.3
Interim mitigation

Apply vendor-provided patches (V2303 or later for Capital Embedded AR Classic R20-11, V0.5.0.0 or later for SIMOTICS CONNECT 400). For unpatchable versions (Capital Embedded AR Classic 431-422, PLUSCONTROL 1st Gen), implement network segmentation and firewall rules to filter malformed TCP packets at network boundaries.

Fix this in Capital Vstar Scoped from the published advisory
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing10.0 h
  • Review / QA4.0 h
32.0 hours of engineering $5,580
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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-2021-31889 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data