CVE-2026-53909
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 · uneditedMCO does not correctly validate types of uploaded files. File upload validation functionality relies only on client-side checks, which can be bypassed. An authorized, low-privileged attacker can upload files with arbitrary types to the server. Because vendor contact attempts were unsuccessful, the vulnerability has only been confirmed in version 25.3.3.1 but may also affect other versions.
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 confidenceMCO's file upload functionality relies solely on client-side validation for file type checking, which can be easily bypassed. An authorized low-privileged attacker can upload files with arbitrary types to the server by modifying client-side requests or using tools to circumvent client-side checks.
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= 25.3.3.1CVSS 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
- None
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/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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Confirm the installed version of MycomplianceofficeCheck your installed Mycomplianceoffice version by accessing the admin panel, About section, or running the product's version command. Compare against version 25.3.3.1.Affected if The installed version is exactly 25.3.3.1.
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Identify if file upload functionality is enabledNavigate to Mycomplianceoffice settings or admin console and locate any file upload, document upload, or attachment features. Check if the file upload module is accessible to users.Affected if File upload functionality exists and is accessible to authorized users.
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Inspect the file upload endpoint configurationUse browser developer tools or a proxy tool to capture a file upload request. Examine the HTTP request/response for the upload endpoint. Check if the server returns any server-side validation responses or if validation appears to occur only in the browser client.Affected if Only client-side JavaScript validation is observed in the upload flow with no server-side validation headers or responses.
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Test for server-side validation bypassModify a legitimate file upload request using a proxy tool. Change the file extension, Content-Type header, or MIME type to a non-image/non-document type (such as .php, .exe, or .html) and submit the request. Observe if the file is accepted and stored on the server.Affected if The server accepts and stores files with arbitrary extensions or MIME types without rejecting them.
You are affected if you run Mycomplianceoffice version 25.3.3.1 with the file upload feature enabled and the server accepts files without proper server-side validation.
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 dataImplement robust server-side file type validation using magic byte/file signature verification, content-type headers, and strict allowlist-based extension checking. Store uploads outside webroot and disable script execution.
- Consultation3.0 h
- Implementation6.0 h
- Testing4.0 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 $4,224.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-53909 — 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-2026-53909 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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- Version or environment caveats, and links to real fixes
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