CVE-2021-40102
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. Arbitrary File deletion can occur via PHAR deserialization in is_dir (PHP Object Injection associated with the __wakeup magic method).
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 confidencePHP Object Injection in Concrete CMS through 8.5.5 allows attackers to achieve arbitrary file deletion via PHAR deserialization exploiting the __wakeup magic method. This deserialization vulnerability enables unauthenticated attackers to delete sensitive files on the server.
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
- None
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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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Determine Concrete CMS versionLog into the Concrete CMS dashboard as an administrator and navigate to the Dashboard > System & Settings > About Concrete CMS page to view the installed version number. Alternatively, check the application/config/app.php file for the version identifier.Affected if The displayed version number is 8.5.5 or lower.
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Verify PHP PHAR deserialization is enabledCreate a PHP file containing 'phpinfo();' and access it in a browser, then search for 'phar.deserialization' or check the PHP configuration. Alternatively, run 'php -i | grep phar' from the command line.Affected if The phar.deserialization setting is On or not explicitly disabled (should show Off to be safe).
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Check for unauthenticated file upload or PHAR handling endpointsReview the Concrete CMS web application for any endpoints that handle file uploads, particularly those accepting PHAR files or processing file paths from unauthenticated sources. Inspect any legacy or third-party file handling code in the /packages or /blocks directories.Affected if The application accepts and processes PHAR files or deserializes objects from PHAR archives without authentication.
You are affected if running Concrete CMS version 8.5.5 or lower AND PHAR deserialization is enabled in your PHP configuration, allowing unauthenticated deserialization of malicious PHAR archives.
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 Concrete CMS beyond version 8.5.5 to receive the security patch. As a temporary measure, disable PHAR deserialization and implement strict input validation on user-controlled file path parameters.
Concrete CMS 8.5.6
- Backup the database and all website files before proceeding
- Download Concrete CMS version 8.5.6 or later from the official concretecms.org website
- Review the official upgrade guide at documentation.concretecms.org for step-by-step instructions
- Upload the new files to the server, replacing the existing installation
- Run the upgrade process by accessing the site URL
- Verify the upgrade was successful by checking the dashboard version number
- Test critical functionality to ensure the site operates correctly after upgrade
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation12.0 h
- Testing6.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-40102 — 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-2021-40102 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