CVE-2021-31228
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 · uneditedAn issue was discovered in HCC embedded InterNiche 4.0.1. This vulnerability allows the attacker to predict a DNS query's source port in order to send forged DNS response packets that will be accepted as valid answers to the DNS client's requests (without sniffing the specific request). Data is predictable because it is based on the time of day, and has too few bits.
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 HCC embedded InterNiche 4.0.1 DNS client implementation uses predictable source ports based on time of day with insufficient entropy bits, allowing attackers to forge DNS responses without sniffing traffic. This enables DNS cache poisoning attacks.
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< 4.3CVSS 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
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
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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Confirm Nichestack is in useSearch your codebase, firmware, or dependencies for InterNiche or Nichestack references. Look for include files such as nbstubs.h, nport.h, or library binaries named libniche or similar.Affected if Nichestack or InterNiche DNS client code or libraries are present in your environment
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Identify the installed Nichestack versionCheck version headers, library manifests, or build documentation for the Nichestack component. Look for version macros like NSTACK_VERSION, NICHESTACK_VERSION, or check the nbstubs.h/nport.h headers.Affected if The discovered version is less than 4.3 (e.g., 4.0.1, 4.1, 4.2, or any version number starting with a value lower than 4.3)
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Verify DNS client module is enabledCheck your project configuration files, build scripts, or makefiles for DNS client feature flags such as NICHEDNS, NSDNS, DNS_CLIENT_ENABLED, or similar preprocessor defines that enable DNS resolution functionality.Affected if DNS client functionality is compiled into or enabled in your build configuration
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Inspect DNS source port generation behaviorReview the DNS client source code for the source port assignment logic. Look for functions that generate ports based on time-of-day functions (e.g., time(), gettimeofday(), clock()) or any non-cryptographic random number generation.Affected if Source ports are computed using time-based values or non-cryptographic randomization without sufficient entropy (less than 16 bits of randomness)
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Check network exposure of DNS serviceVerify whether the DNS client communicates with external DNS servers over the network or is used in a context where untrusted DNS responses could be received.Affected if The DNS client processes responses from network sources and is not protected by additional validation or secure channel mechanisms
You are affected if you use Hcc Embedded Nichestack version less than 4.3 with the DNS client enabled and the source port generation relies on time-based or low-entropy randomization.
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.
dbcve · scoped4.3
Replace time-of-day-based source port generation with cryptographically secure random number generation using sufficient entropy (e.g., RFC 5452 recommends random source ports from the full 16-bit range).
Nichestack 4.3 or later
- 1. Identify all deployed instances of HCC Embedded InterNiche/Nichestack in your environment
- 2. Check current Nichestack version on each device/system
- 3. Obtain the fixed version (Nichestack 4.3 or later) from HCC Embedded through their official support channels
- 4. Review release notes and documentation for the target version to understand any API or configuration changes
- 5. Create a backup of current configurations and firmware
- 6. Test the upgrade in a staging or lab environment before deploying to production
- 7. Apply the upgrade to production systems following your organization's change management process
- 8. Verify the upgrade was successful and DNS functionality is working correctly
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 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 $6,176.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-31228 — 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-2021-31228 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
- No weaponised exploit code, or anything meant to cause harm
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