CVE-2021-31337
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 · uneditedThe Telnet service of the SIMATIC HMI Comfort Panels system component in affected products does not require authentication, which may allow a remote attacker to gain access to the device if the service is enabled. Telnet is disabled by default on the SINAMICS Medium Voltage Products (SINAMICS SL150: All versions, SINAMICS SM150: All versions, SINAMICS SM150i: All versions).
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 Telnet service on SIMATIC HMI Comfort Panels lacks authentication requirements, allowing remote unauthenticated attackers to access the device if Telnet is enabled. This provides a direct vector to the underlying system with potential for remote code execution or credential harvesting.
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 dataall versionsall versionsall versionsCVSS 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 checksWork through these to decide whether this CVE applies to you.
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Identify device model and firmware versionAccess the device management interface or use Siemens engineering tools (like Startdrive or S7) to retrieve the exact model number (Sl150, Sm150, or Sm150i) and firmware version. This is typically found under device properties or system info.Affected if The device model is Siemens Sinamics Sl150, Sm150, or Sm150i (any firmware version)
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Locate Telnet service configurationAccess the device web interface, SINAMICS Startdrive, or device management console. Navigate to Communication settings or Services configuration panel to find the Telnet service settings.Affected if Telnet service is listed as enabled or active in the service configuration
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Verify Telnet service statusAttempt to connect to the device on TCP port 23 using a Telnet client or network scanner (e.g., `nc -zv <device_ip> 23` or `telnet <device_ip>`). Alternatively, check if port 23 is listening via port scan.Affected if Telnet service responds on port 23, indicating it is actively running and accessible
The environment is affected if the device is a Sinamics Sl150, Sm150, or Sm150i with Telnet service enabled and accessible, since the lack of authentication applies whenever Telnet is active on these devices.
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 dataDisable the Telnet service on affected devices if not required for operations. If Telnet is essential, implement strict network segmentation and firewall rules to limit Telnet access to authorized IPs only, and monitor for unauthorized access attempts.
- Consultation2.0 h
- Implementation4.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-31337 — 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-2021-31337 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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