CVE-2021-28931
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 · uneditedArbitrary file upload vulnerability in Fork CMS 5.9.2 allows attackers to create or replace arbitrary files in the /themes directory via a crafted zip file uploaded to the Themes panel.
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 confidenceArbitrary file upload vulnerability in Fork CMS 5.9.2 allows attackers to upload a crafted ZIP file through the Themes panel that, upon extraction, writes files to the /themes directory, enabling creation or replacement of arbitrary 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= 5.9.2CVSS 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
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/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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Verify Fork CMS versionCheck the installed version of Fork CMS by accessing the admin dashboard version information or inspecting the application files for a version marker (commonly in a composer.json, core version file, or admin about page)Affected if The installed version is exactly 5.9.2
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Confirm Themes panel accessLog into the Fork CMS admin panel and navigate to the Themes section to verify the functionality exists and is accessibleAffected if The Themes panel is available and accessible in the admin interface
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Check ZIP upload capabilityIn the Themes panel, verify if the option to upload theme packages (ZIP files) is present or enabled for the user roleAffected if ZIP file upload functionality in the Themes panel is enabled and accessible
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Inspect themes directoryExamine the /themes directory in the web root for any unexpected or recently added files that do not correspond to installed themesAffected if Unexpected files exist in the /themes directory or file permissions allow write access to extracted content
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Review upload logsCheck server access and application logs for any ZIP file uploads through the Themes panel, particularly from unusual sources or timesAffected if Log entries show ZIP uploads through the Themes module that may indicate exploitation
Your environment is affected if Fork CMS version 5.9.2 is installed and the Themes panel with ZIP upload functionality is accessible, allowing path traversal during ZIP extraction to write files outside intended boundaries.
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 dataValidate and sanitize ZIP file contents before extraction, implement path traversal checks, restrict extracted file locations, and consider upgrading to a patched version if available.
- Consultation3.0 h
- Implementation6.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,984.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-28931 — 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-2021-28931 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