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Nut\/osOperating system · Ethernut

CVE-2020-25109

CRITICAL · 9.8 CVSS v3.1 Published 2020-12-11
Fix available
A fix is available. Upgrade to after 5.1 or later.
See remediation →
100/100
Remediation priority · Urgent
High EPSS 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
An issue was discovered in the DNS implementation in Ethernut in Nut/OS 5.1. The number of DNS queries/responses (set in a DNS header) is not checked against the data present. This may lead to successful Denial-of-Service, and possibly Remote Code Execution.

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 · moderate confidence

The DNS implementation in Ethernut Nut/OS 5.1 fails to validate the number of DNS queries/responses specified in the DNS header against the actual data received. This missing bounds check allows malformed DNS packets to trigger buffer handling errors, leading to denial of service and potentially enabling remote code execution.

MitigationImplement strict validation of DNS header fields, specifically checking that the declared query/response count matches the actual data length before processing. Update to any available patched version of Nut/OS if released.

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
Nut\/osOperating system
Affected:<= 5.1

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. Confirm Ethernut Nut/OS installation and version
    Identify if the target system runs Ethernut Nut/OS and determine the installed version. On embedded systems, check system information files, boot logs, or firmware metadata that contain OS version strings. Compare the discovered version against the affected range: any Nut/OS version 5.1 or lower is potentially vulnerable.
    Affected if The system runs Ethernut Nut/OS version 5.1 or lower.
  2. Determine if DNS service is enabled
    Inspect the Nut/OS configuration or running services to check whether the DNS client or DNS server functionality is active. On embedded systems, review the compiled configuration (often in a .cfg file or flash memory) or check running tasks/processes related to DNS (such as dnsd, resolver, or network services).
    Affected if DNS functionality is enabled in the Nut/OS configuration.
  3. Verify DNS packet handling configuration
    Examine the DNS configuration files or settings in the Nut/OS environment for any parameters controlling DNS packet processing. Look for configuration options related to maximum query counts, buffer sizes, or validation flags. If accessible, check the compiled DNS module source code or binary for any bounds-checking logic.
    Affected if No explicit bounds-checking or validation is configured for DNS packet header fields, or the DNS module lacks validation code.
  4. Inspect DNS traffic or logs for malformed packets
    If network capture or DNS transaction logs are accessible, examine recent DNS traffic for packets where the header-specified query count does not match the actual records in the payload. Check system logs for any error messages related to DNS buffer overflows, memory corruption, or service crashes.
    Affected if Malformed DNS packets are being processed without rejection, or DNS-related crash logs exist.

A system is affected if it runs Ethernut Nut/OS version 5.1 or lower with DNS functionality enabled and lacks proper validation of DNS header query/response counts against received packet data.

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 a release after 5.1
Interim mitigation

Implement strict validation of DNS header fields, specifically checking that the declared query/response count matches the actual data length before processing. Update to any available patched version of Nut/OS if released.

Fix this in Nut\/os Scoped from the published advisory
  • Consultation4.0 h
  • Implementation6.0 h
  • Testing8.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,800
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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-2020-25109 in production — separate from our analysis above.

No notes yet

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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
  • 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