CVE-2026-30821
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 · uneditedFlowise is a drag & drop user interface to build a customized large language model flow. Prior to version 3.0.13, the /api/v1/attachments/:chatflowId/:chatId endpoint is listed in WHITELIST_URLS, allowing unauthenticated access to the file upload API. While the server validates uploads based on the MIME types defined in chatbotConfig.fullFileUpload.allowedUploadFileTypes, it implicitly trusts the client-provided Content-Type header (file.mimetype) without verifying the file's actual content (magic bytes) or extension (file.originalname). Consequently, an attacker can bypass this restriction by spoofing the Content-Type as a permitted type (e.g., application/pdf) while uploading malicious scripts or arbitrary files. Once uploaded via addArrayFilesToStorage, these files persist in backend storage (S3, GCS, or local disk). This vulnerability serves as a critical entry point that, when chained with other features like static hosting or file retrieval, can lead to Stored XSS, malicious file hosting, or Remote Code Execution (RCE). This issue has been patched in version 3.0.13.
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 confidenceFlowise versions before 3.0.13 have an unauthenticated file upload vulnerability in the /api/v1/attachments endpoint. The server validates file types based on client-provided Content-Type headers without verifying actual file content (magic bytes) or extension, allowing attackers to bypass restrictions by spoofing permitted types (e.g., application/pdf) to upload malicious scripts or arbitrary files that persist in backend storage.
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< 3.0.13CVSS 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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Check Flowise versionLocate the package.json file in the Flowise installation directory and find the 'version' field, or query the Flowise API endpoint /api/v1/version if availableAffected if The installed version is anything less than 3.0.13
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Verify attachment upload endpoint authenticationSend a request to the /api/v1/attachments/:chatflowId/:chatId endpoint without providing any authentication credentials and observe the responseAffected if The endpoint returns a successful response (2xx) without requiring authentication, indicating it is exposed without access controls
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Inspect file upload storage configurationExamine the Flowise configuration file (config.json, .env, or environment variables) for storage settings - look for storage configurations such as S3_BUCKET_NAME, GCS_BUCKET_NAME, or LOCAL_STORAGE_PATHAffected if Storage is configured to persist uploaded files (S3, GCS, or local storage) and the attachments endpoint is unauthenticated
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Test Content-Type validation behaviorUpload a file to /api/v1/attachments/:chatflowId/:chatId with a spoofed Content-Type header (e.g., set Content-Type to application/pdf but upload a non-PDF file) and check if the file is acceptedAffected if The server accepts and stores the file based solely on the client-provided Content-Type header without validating the actual file content or extension
A user is affected if they are running any Flowise version below 3.0.13 and the attachments upload endpoint is accessible without authentication, allowing arbitrary file uploads to persist in storage.
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 · scoped3.0.13
Upgrade to Flowise version 3.0.13 or later, and implement server-side validation of file content (magic bytes) and file extensions rather than trusting client-provided Content-Type headers.
Flowise 3.0.13
- 1. Backup your current Flowise installation and any uploaded files
- 2. Upgrade Flowise to version 3.0.13 or later by pulling the latest Docker image or using your package manager
- 3. Verify the upgrade was successful by checking the version (e.g., via UI or CLI)
- 4. Test file upload functionality to confirm the patch is working correctly
- 5. Review WHITELIST_URLS configuration to ensure no other unintended unauthenticated endpoints exist
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation6.0 h
- Testing3.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-30821 — 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-2026-30821 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
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