CVE-2021-40098
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 · uneditedAn issue was discovered in Concrete CMS through 8.5.5. Path Traversal leading to RCE via external form by adding a regular expression.
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 confidenceA path traversal vulnerability in Concrete CMS through version 8.5.5 allows remote attackers to achieve Remote Code Execution by exploiting the external form feature through manipulation of regular expression parameters.
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<= 8.5.5CVSS 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 the installed Concrete CMS versionAccess the dashboard and navigate to Dashboard > System & Settings > Basics > Maintenance Mode, or check the file /application/config/database.php for version info, or look at the footer of any admin page for the version numberAffected if The version is 8.5.5 or lower (any version through 8.5.5)
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Determine if the external form feature is activeCheck if the External Form add-on is installed and enabled by reviewing the list of installed packages in Dashboard > Extend Concrete CMS, or attempt to access the external form handler at /tools/required/external_formAffected if The external form feature is installed and accessible on the site
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Review external form submissions for manipulated regex parametersInspect web server access logs for requests to external form endpoints containing regex patterns (e.g., containing .. for path traversal sequences, or preg_* parameters)Affected if There are logged requests with path traversal sequences (..) or suspicious regex parameters in external form URLs
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Check for unauthorized file creation or modificationReview the /application/blocks/ or /packages/ directories for unexpected files, or check file system integrity comparing against known good backupsAffected if New or modified files exist in the CMS directories that were not intentionally deployed
You are affected if running Concrete CMS version 8.5.5 or lower AND the external form feature is enabled and accessible on your site.
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.
dbcve · scopedUpgrade to Concrete CMS version 8.5.6 or later which contains the patched code, or apply vendor-released patches to address the path traversal vulnerability in the external form handling component.
Concrete CMS 8.5.6 or later
- Upgrade Concrete CMS from version 8.5.5 or lower to version 8.5.6 or later
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation6.0 h
- Implementation12.0 h
- Testing8.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-40098 — 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-2021-40098 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
- No spam, self-promotion, credentials, or personal data