CVE-2020-17470
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 FNET through 4.6.4. The code that initializes the DNS client interface structure does not set sufficiently random transaction IDs (they are always set to 1 in _fnet_dns_poll in fnet_dns.c). This significantly simplifies DNS cache poisoning attacks.
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 FNET TCP/IP stack's DNS client in fnet_dns.c always sets transaction IDs to 1 in the _fnet_dns_poll function instead of generating random values. This predictable ID makes DNS cache poisoning attacks significantly easier to execute.
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<= 4.6.4CVSS 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
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/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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Identify FNET stack presenceSearch for files named fnet_dns.c or FNET library references in the project source or firmware imageAffected if FNET TCP/IP stack is present in the environment
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Determine FNET versionCheck the FNET version header file or library version metadata; common locations include fnet.h or version definition filesAffected if The installed FNET version is 4.6.4 or earlier
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Inspect DNS transaction ID source codeOpen fnet_dns.c and locate the _fnet_dns_poll function; examine the code where transaction IDs are assigned to DNS queriesAffected if The transaction ID is hardcoded to a static value (such as 1) rather than a randomly generated value
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Verify DNS client is in useCheck project configuration files or build settings for DNS client module enablement (such as FNET_CFG_DNS or similar configuration flags)Affected if DNS client functionality is enabled and actively resolving hostnames
The environment is affected if it uses FNET stack version 4.6.4 or earlier with the DNS client enabled and the source code shows a static (non-random) transaction ID assignment in fnet_dns.c.
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 dataReplace the static transaction ID assignment with a cryptographically secure random number generator suitable for the embedded environment, ensuring each DNS query uses a unique unpredictable ID.
- Consultation2.0 h
- Implementation3.0 h
- Testing3.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-17470 — 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-2020-17470 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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