CVE-2021-40103
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 can lead to Arbitrary File Reading and SSRF.
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 confidenceA path traversal vulnerability in Concrete CMS versions up to 8.5.5 allows unauthenticated attackers to read arbitrary files on the server filesystem and perform Server-Side Request Forgery (SSRF) attacks. The vulnerability stems from insufficient input validation in file handling operations.
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
- 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 Concrete CMS versionLog into the CMS dashboard and navigate to Dashboard > System & Settings > About Concrete CMS, or check the composer.json file if accessible via the web rootAffected if The version displayed is 8.5.5 or any version lower than 8.5.6
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Review web server access logs for path traversal patternsSearch access logs (commonly found in /var/log/nginx/, /var/log/apache2/, or similar) for requests containing '../' sequences in URL parametersAffected if Unauthenticated requests with '../' patterns are present in the logs targeting file-related endpoints
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Check for SSRF indicators in network logsReview outbound HTTP requests from the web server for unusual destinations or requests to internal network resources that were not initiated by legitimate usersAffected if Outbound requests to internal IP addresses, cloud metadata endpoints, or unexpected external domains appear in the logs
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Audit file system for unauthorized accessCheck web root and system directories for any recently created or modified files that were not uploaded through the legitimate CMS file managerAffected if Unexpected files or directories exist that were not created through authorized CMS operations
A system is affected if it runs Concrete CMS version 8.5.5 or lower and has unauthenticated file handling endpoints accessible 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.
dbcve · scopedUpgrade Concrete CMS to version 8.5.6 or later. If patching is not immediately possible, implement web application firewall rules to block path traversal sequences (../) in request parameters and restrict file access permissions.
Concrete CMS 8.5.6 or later (or latest 8.x/9.x stable release)
- 1. Back up your Concrete CMS database and files before upgrading.
- 2. Download the latest stable release of Concrete CMS from the official repository (github.com/concretecms/concrete_cms).
- 3. Review the release notes for the version you plan to upgrade to, specifically looking for security fixes.
- 4. Upload the new files to your server, replacing the core files while preserving your config/site-specific files.
- 5. Run any database migrations if required by accessing the dashboard or running console commands.
- 6. Clear all caches through the dashboard or by removing files in /application/files/cache/.
- 7. Verify the upgrade by logging in and checking that the path traversal vulnerability is no longer present.
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation6.0 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-2021-40103 — 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-2021-40103 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