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Capital VstarApplication · Siemens

CVE-2021-31884

CRITICAL · 9.8 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 →
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 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), Capital VSTAR (All versions with enabled Ethernet options), 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). The DHCP client application assumes that the data supplied with the “Hostname” DHCP option is NULL terminated. In cases when global hostname variable is not defined, this may lead to Out-of-bound reads, writes, and Denial-of-service conditions. (FSMD-2021-0014)

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 DHCP client application in multiple Siemens building automation controllers and Nucleus RTOS does not properly validate the length of the Hostname DHCP option, assuming it is NULL-terminated. When the global hostname variable is undefined, this causes out-of-bounds memory reads and writes, leading to potential code execution and denial-of-service conditions.

MitigationApply vendor firmware updates where available (APOGEE PXC and TALON require V3.5.4 or later for BACnet, V2.8.19 or later for P2 Ethernet; Desigo requires V6.30.016 or later). For unpatched devices, isolate on a dedicated network segment and consider using static IP addressing instead of DHCP to avoid processing malicious hostname options.

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:< 2017.02.1
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

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
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/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 device firmware or software product and version
    Access the device management interface, web UI, or system information to determine the exact firmware version (e.g., Apogee PXC Compact, PXC Modular) or software version (e.g., Nucleus Readystart V3). Compare against the affected version ranges provided.
    Affected if The product is any of: Siemens Capital Vstar (any version), Siemens Nucleus Net (any version), Nucleus Readystart V3 (version below 2017.02.1), Nucleus Source Code (any version), Apogee Modular Building Controller (any version), Apogee Modular Equipment Controller (any version), Apogee PXC Compact (
  2. Determine whether DHCP client is enabled
    Check the network configuration settings on the device or controller. Look for DHCP client settings in the network/IP configuration menu, web interface, or configuration files. Confirm if DHCP is set to 'enabled' or if the device is configured to obtain IP address automatically.
    Affected if DHCP client is enabled on the device, as this is the attack vector for sending malicious Hostname DHCP options to the client.
  3. Verify hostname configuration status
    Check the DHCP client hostname or system hostname configuration setting on the device. Determine whether the global hostname variable is defined/configured or left undefined/blank in the DHCP client settings.
    Affected if The hostname variable is undefined, blank, or not explicitly configured in the DHCP client settings, which is the specific condition that triggers the out-of-bounds memory access.

The device is affected if it runs any of the affected product versions AND uses DHCP client with an undefined hostname configuration, allowing a malicious DHCP server to exploit the unsanitized Hostname option length.

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 2.8.19 / 3.5.4 / 2017.02.1 or later
Fixed in 2.8.193.5.42017.02.1
Interim mitigation

Apply vendor firmware updates where available (APOGEE PXC and TALON require V3.5.4 or later for BACnet, V2.8.19 or later for P2 Ethernet; Desigo requires V6.30.016 or later). For unpatched devices, isolate on a dedicated network segment and consider using static IP addressing instead of DHCP to avoid processing malicious hostname options.

Fix this in Capital Vstar Scoped from the published advisory
  • Consultation8.0 h
  • Implementation16.0 h
  • Testing12.0 h
  • Review / QA8.0 h
44.0 hours of engineering $7,720
Get the upgrade done

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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-2021-31884 in production — separate from our analysis above.

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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
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  • Version or environment caveats, and links to real fixes
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