CVE-2021-36763
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 CODESYS V3 web server before 3.5.17.10, files or directories are accessible to External Parties.
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 confidenceCODESYS V3 web server before version 3.5.17.10 contains a directory traversal or improper access control vulnerability that allows external parties to access sensitive files and directories on the server. This is a network-exploitable issue requiring no authentication, with high confidentiality impact but no integrity or availability impact per CVSS.
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< 4.2.0.0<= 4.2.0.0< 3.5.17.10< 3.5.17.10< 3.5.17.10< 3.5.17.10< 3.5.17.10< 3.5.17.10CVSS 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
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
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 CODESYS V3 web server installationLook for CODESYS installation directories (typically in C:\Program Files\CODESYS or /opt/codesys) and check for the 'CODESYS Web Server' or 'WebServer' component. On Windows, check installed programs or services for CODESYS-related entries.Affected if CODESYS V3 web server component is present on the system
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Determine installed CODESYS versionLocate the version information in the CODESYS installation, typically found in the About dialog, the main executable file properties (right-click on CoDeSysSP.exe or similar), or in registry keys under HKEY_LOCAL_MACHINE\SOFTWARE\CODESYS or HKEY_LOCAL_MACHINE\SOFTWARE\3S-Smart Software Solutions.Affected if Version cannot be determined or is lower than 3.5.17.10 for 3.x products, or lower than 4.2.0.0 for the 4.x product line
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Verify web server network accessibilityCheck if the CODESYS web server is running and listening on its configured port (default HTTP port 8080 or 80). Use netstat -an | findstr "8080" or similar command to identify listening ports, or check the web server configuration file (often webserver.cfg or in the CODESYS Gateway settings).Affected if Web server is listening on an accessible network port (0.0.0.0 or external IP binding) and version is within affected range
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Confirm web server is not patchedIf version is determined to be 3.5.17.10 or later, or 4.2.0.0 or later for the respective product lines, the vulnerability is patched. Compare your exact installed version against the affected version thresholds: 3.5.17.10 for Control Rte, Runtime System Toolkit, Win Sl, Embedded Target Visu Toolkit, Hmi, and Remote Target Visu Toolkit; 4.2.0.0 for Codesys Control.Affected if Installed version is below 3.5.17.10 (for most products) or below 4.2.0.0 (for Codesys Control) and the web server is network-accessible
The environment is affected if a CODESYS V3 web server component is installed with a version below 3.5.17.10 (or 4.2.0.0 for Codesys Control) and is accessible over the network, since this directory traversal flaw can be exploited remotely without authentication.
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 data3.5.17.104.2.0.0
Update CODESYS V3 web server to version 3.5.17.10 or later to obtain the vendor patch. If immediate patching is not possible, restrict network access to the web server via firewall rules or network segmentation.
- Consultation2.0 h
- Implementation2.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-36763 — 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-2021-36763 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
- No spam, self-promotion, credentials, or personal data