CVE-2021-38387
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 · uneditedIn Contiki 3.0, a Telnet server that silently quits (before disconnection with clients) leads to connected clients entering an infinite loop and waiting forever, which may cause excessive CPU consumption.
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 confidenceThe Contiki 3.0 Telnet server contains a flaw where it exits silently (without proper disconnection handshake) before notifying connected clients. This causes client connections to hang indefinitely in a waiting state, consuming CPU resources in an infinite loop as they await a response that never arrives.
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= 3.0CVSS 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.
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Identify Contiki OS versionCheck system files, build configuration, or firmware metadata for the Contiki version string. Common locations: README, version.h, or build system output.Affected if Version is exactly 3.0 (Contiki 3.0)
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Confirm Telnet server is enabledReview Contiki configuration files (contiki-conf.h, project-conf.h) or build settings for Telnet server compilation flags such as NETSTACK_CONF_WITH_TELNET or similar Telnet-related preprocessor definitions.Affected if Telnet server feature is compiled into the firmware or actively configured
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Check Telnet server implementationExamine the Telnet server source code (typically in apps/telnet/ or similar) for proper session termination handling. Look for missing telnet_close() or telnet_exit() calls before main loop termination.Affected if The Telnet server lacks proper disconnect notification before exiting
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Test client connection behaviorConnect a Telnet client to the device, then trigger a server exit or system restart. Observe whether the client connection hangs indefinitely rather than receiving a proper disconnect response.Affected if Client connection hangs and consumes CPU in a waiting state after server exits
A user is affected if they are running Contiki 3.0 with the Telnet server enabled, and clients experience hanging connections when the Telnet server terminates unexpectedly.
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 dataImplement proper session termination and client notification in the Telnet server, or add connection timeout handling on the client side to prevent indefinite waiting when the server unexpectedly terminates.
- Consultation3.0 h
- Implementation6.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,224.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-38387 — 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-2021-38387 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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