CVE-2026-50873
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 arbitrary file upload vulnerability in the attachment handling component of flatnotes v5.5.4 allows attackers to execute arbitrary code via uploading a crafted HTML or SVG file.
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 confidenceThe attachment handling component in flatnotes v5.5.4 lacks proper validation of uploaded files, allowing attackers to upload malicious HTML or SVG files containing embedded scripts or code. When these files are subsequently accessed or rendered by the application or users, the embedded code executes, leading to arbitrary code execution on the server.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS 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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Confirm flatnotes installationIdentify if flatnotes is running in your environment by checking for the flatnotes service, container, or Python process. Look for flatnotes-related processes or check the application directory structure.Affected if flatnotes is not present in your environment
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Check flatnotes versionLocate the installed version of flatnotes. Common methods: check the running container tag, look for version in requirements.txt, check the pip package version with 'pip show flatnotes', or inspect the flatnotes source for a version identifier.Affected if the installed version is v5.5.4 or falls within the affected range around v5.5.4
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Verify file upload functionality is enabledExamine the flatnotes configuration file (typically config.yaml or settings file) for attachment/upload-related settings. Check if file attachments are enabled in the application settings or environment variables.Affected if file uploads or attachments are enabled in the configuration
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Inspect uploaded file storage locationCheck the flatnotes data directory to see where uploaded files are stored. Look for an 'attachments' or 'uploads' folder within the flatnotes data directory. Determine if this folder is accessible via the web server (within webroot).Affected if uploaded files are stored in a directory accessible via the web (within webroot)
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Check file type validation on uploadsReview flatnotes configuration or source code to determine if file type validation exists. Look for allowlists, extension checks, MIME type verification, or content-based (magic byte) validation in the upload handling code.Affected if there is no file type validation or the validation only checks extensions without content inspection, allowing HTML or SVG files to be uploaded
If flatnotes v5.5.4 is running with file upload enabled and uploaded files are stored in a web-accessible location without strict allowlist-based file type validation, the environment is affected by this vulnerability.
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 strict allowlist-based file type validation (checking both extension and MIME type) and disable script execution in uploaded files by storing them outside webroot or using Content-Disposition: attachment headers; consider content-based file type detection using magic bytes.
- Consultation4.0 h
- Implementation12.0 h
- Testing6.0 h
- Review / QA3.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-50873 — 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-2026-50873 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