CVE-2021-31882
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 Capital Embedded AR Classic 431-422 (All versions), Capital Embedded AR Classic R20-11 (All versions < V2303). The DHCP client application does not validate the length of the Domain Name Server IP option(s) (0x06) when processing DHCP ACK packets. This may lead to Denial-of-Service conditions. (FSMD-2021-0011)
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 DHCP client in Capital Embedded AR Classic fails to validate the length field of Domain Name Server IP options (option code 0x06) when processing DHCP ACK packets. An attacker on the local network could send a malicious DHCP response with an invalid DNS option length, causing the client to misprocess the data and trigger a denial-of-service condition.
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 dataall versionsall versions< 2017.02.1all versionsall versionsall versionsall versionsall 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
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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 checksWork through these to decide whether this CVE applies to you.
-
Identify the embedded product and firmware versionLocate the system firmware or software version through the device's web interface, boot logs, or by extracting the firmware image. Common locations: /etc/version, U-boot environment, or manufacturer documentation.Affected if The product matches one of the affected products (Capital Vstar, Nucleus Net, Nucleus Readystart V3, Nucleus Source Code, or Apogee firmware variants) and the version falls within the affected range (e.g., Nucleus Readystart V3 < 2017.02.1).
-
Verify DHCP client is enabled and in useCheck the system configuration or running processes for DHCP client functionality. Inspect network configuration files (e.g., /etc/network/interfaces, udhcpc, dhclient configuration) or check if the DHCP client daemon is running.Affected if The device uses a DHCP client to obtain IP configuration, making it vulnerable to malicious DHCP responses.
-
Check network exposure to local attackersEvaluate whether the device resides on a network segment where an untrusted attacker could inject malicious DHCP responses. This includes checking network topology, switch port security, and whether the network is shared or trusted.Affected if The device is on a network where a rogue DHCP server can be positioned to respond to the client's DHCP requests.
-
Confirm the DHCP client implementation uses the vulnerable codeIf possible, examine the DHCP client binary or source code for the specific function handling DNS option (0x06) parsing in DHCP ACK packets. Check whether length validation exists before processing the DNS server list.Affected if The DHCP client lacks proper length validation for DNS option 0x06 in DHCP ACK packets, allowing malformed responses to trigger the denial-of-service condition.
The environment is affected if it uses any of the listed Siemens products with the vulnerable DHCP client code and operates on a network where a local attacker could inject malicious DHCP responses with malformed DNS options.
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 data2017.02.1
Upgrade to Capital Embedded AR Classic R20-11 version V2303 or later which contains the fix; additionally, network segmentation and rogue DHCP server protection can limit exposure to attacks.
- Consultation4.0 h
- Implementation8.0 h
- Testing12.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $7,616.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-31882 — 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-2021-31882 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
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
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.
- 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