CVE-2021-22699
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 · uneditedImproper Input Validation vulnerability exists in Modicon M241/M251 logic controllers firmware prior to V5.1.9.1 that could cause denial of service when specific crafted requests are sent to the controller over HTTP.
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 confidenceImproper input validation in the HTTP server of Schneider Electric Modicon M241 and M251 logic controllers allows remote attackers to send crafted HTTP requests that cause a denial of service condition. The vulnerability exists in firmware versions prior to V5.1.9.1.
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< 5.1.9.1< 5.1.9.1CVSS 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 the Modicon controller modelLocate the physical device label or check the device configuration/management interface to confirm the model is either Modicon M241 or Modicon M251.Affected if The device is not a Modicon M241 or M251 controller.
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Check if HTTP server feature is enabledAccess the controller's web management interface or review the controller configuration to verify whether the built-in HTTP server is currently enabled.Affected if HTTP server is enabled and accessible on the network.
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Determine the installed firmware versionConnect to the controller via EcoStruxure Machine Advisor, Unity Pro/Studio, or the device's web interface and locate the firmware version information displayed in the system info or diagnostics section.Affected if The displayed firmware version is lower than V5.1.9.1 (for example, V5.1.8.0 or earlier).
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Compare firmware version against affected rangeCompare the identified firmware version number to the affected range: any version prior to V5.1.9.1 is vulnerable. Note the full version string including any build numbers if displayed.Affected if Firmware version is < V5.1.9.1 and HTTP server is enabled.
A user is affected if they have a Modicon M241 or M251 controller with HTTP server enabled and firmware version lower than V5.1.9.1.
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 data5.1.9.1
Upgrade Modicon M241/M251 firmware to version V5.1.9.1 or later to remediate this vulnerability. Additionally, consider network segmentation to limit HTTP exposure of industrial controllers.
- Consultation6.0 h
- Implementation4.0 h
- Testing8.0 h
- Review / QA4.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2021-22699 — 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-2021-22699 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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- Version or environment caveats, and links to real fixes
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