CVE-2020-27009
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 · uneditedA 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 Source Code (Versions including affected DNS modules), TALON TC Compact (BACnet) (All versions < V3.5.5), TALON TC Modular (BACnet) (All versions < V3.5.5). The DNS domain name record decompression functionality does not properly validate the pointer offset values. The parsing of malformed responses could result in a write past the end of an allocated structure. An attacker with a privileged position in the network could leverage this vulnerability to execute code in the context of the current process or cause a denial-of-service condition.
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 confidenceThe DNS domain name record decompression in Nucleus NET does not validate pointer offset values during parsing of DNS responses, leading to an out-of-bounds write past the end of an allocated structure. This buffer overflow can be triggered by malformed DNS responses, allowing an attacker with privileged network position to achieve code execution in the process context or cause a denial of service.
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< 5.2all versionsCVSS 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
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:H/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 checksWork through these to decide whether this CVE applies to you.
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Identify Nucleus NET installationLocate the Nucleus NET component in your system. This is typically embedded in products like Siemens APOGEE PXC, TALON TC, or other Siemens industrial control devices. Check product documentation or system files for the presence of the Nucleus NET network stack.Affected if Nucleus NET is found on the system and its version is below 5.2, or if using Nucleus Source Code of any version.
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Determine the installed Nucleus NET versionCheck the version information of the Nucleus NET component. This may be available in system firmware, software manifests, or device firmware files. Compare the version number against the affected range (versions prior to 5.2 are vulnerable).Affected if The installed version is Nucleus NET with a version number less than 5.2.
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Verify DNS client or server functionality is enabledInspect the Nucleus NET configuration to determine if DNS resolution or DNS server functionality is active. Look for DNS-related configuration files or settings that enable DNS response processing.Affected if DNS client or DNS server features are enabled and the system processes DNS responses from the network.
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Check for DNS response processing in the network stackReview network traffic or logs to confirm the system is accepting and parsing DNS responses. This vulnerability is triggered specifically when the system parses DNS responses containing domain name records.Affected if The system processes DNS responses from the network as part of its normal operation.
A system is affected if it runs Nucleus NET version below 5.2 (or any version of Nucleus Source Code) and has DNS response parsing enabled, allowing malformed DNS responses to trigger the buffer overflow.
Generated from the published advisory. Verify against your own configuration.
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 data5.2
Upgrade the affected Siemens products (APOGEE PXC, TALON TC, Nucleus NET) to the fixed versions specified (V3.5.5 for BACnet variants, V2.8.20 for P2 Ethernet, V5.2 for Nucleus NET) or apply Nucleus patches for the DNS module.
- Consultation12.0 h
- Implementation16.0 h
- Testing20.0 h
- Review / QA8.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-27009 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2020-27009 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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