CVE-2021-42147
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 · uneditedBuffer over-read vulnerability in the dtls_sha256_update function in Contiki-NG tinyDTLS through master branch 53a0d97 allows remote attackers to cause a denial of service via crafted data packet.
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 confidenceBuffer over-read vulnerability in the dtls_sha256_update function of Contiki-NG tinyDTLS allows remote attackers to cause denial of service by sending specially crafted DTLS packets. The vulnerability occurs during SHA256 hash updates when processing incoming data, leading to reading beyond allocated buffer boundaries.
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= 2018-08-30CVSS 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
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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.
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Identify if Contiki-NG with tinyDTLS is in useLocate the tinyDTLS library in your codebase or compiled firmware. Search for the dtls_sha256_update function definition or look for tinyDTLS-related files, directories, or embedded firmware components.Affected if Contiki-NG with tinyDTLS is present in your environment
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Check the tinyDTLS version or build dateExamine the tinyDTLS library version, commit hash, or build timestamp. Check for version markers, git tags, or embedded version strings in the tinyDTLS binary or source files.Affected if The version matches the 2018-08-30 release or the build date is on or before 2018-08-30
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Verify DTLS support is enabledInspect the Contiki-NG configuration files (such as project-conf.h or Makefile) for DTLS-related compile flags like DTLS_ENABLED, WITH_DTLS, or USE_TINYDTLS. Check if the dtls module is included in the build.Affected if DTLS support is compiled into the firmware and actively used for secure communications
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Confirm the dtls_sha256_update function exists in the buildSearch the compiled binary or source code for the dtls_sha256_update function. Use tools like nm, objdump, or grep to find the symbol in the firmware image.Affected if The dtls_sha256_update function is present in the compiled firmware
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Inspect network exposure to DTLS trafficReview the device configuration to determine if it accepts incoming DTLS connections or processes DTLS packets from network sources.Affected if The device processes DTLS packets from untrusted network sources
You are affected if your Contiki-NG firmware uses tinyDTLS from the 2018-08-30 release (or earlier unpatched versions) with DTLS enabled and exposed to network traffic.
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 dataApply the available patch for CVE-2021-42147 to tinyDTLS. If no patch exists, implement bounds checking in dtls_sha256_update to validate buffer lengths before reading. Update to a patched version of Contiki-NG that includes the fix.
- Consultation4.0 h
- Implementation8.0 h
- Testing8.0 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 $6,656.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-42147 — 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-2021-42147 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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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
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