Flowise has Arbitrary File Upload via MIME Spoofing

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.2 · CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-30821: 16.71% estimated exploitation activity in the next 30 days; percentile 97.04 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Vulnerability Description --- Vulnerability Overview - The /api/v1/attachments/:chatflowId/:chatId endpoint is listed in WHITELISTURLS, 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). Vulnerable…

Published by the source

6 Mar 2026, 18:49 UTC

Last modified by the source

9 Mar 2026, 13:31 UTC

Source last checked

26 Oct 2026, 12:43 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-j8g8-j7fc-43v6

2. Revision 2 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-j8g8-j7fc-43v6

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-30821

Advisory: Flowise has Arbitrary File Upload via MIME Spoofing
IDs: CVE-2026-30821, GHSA-j8g8-j7fc-43v6
Record: https://patchnext.com/advisories/cve-2026-30821 (revision 3, source checked 26 Oct 2026, 12:43 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: flowise 3.0.13. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm flowise: affected <= 3.0.12; fixed in 3.0.13

## Suggested inspection (read-only)
- `npm ls flowise --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on flowise.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-j8g8-j7fc-43v6 (OSV record GHSA-j8g8-j7fc-43v6 lists affected ranges: npm flowise >=0 <3.0.13 (fixed))
- Verified: https://github.com/advisories/GHSA-j8g8-j7fc-43v6 (GitHub-reviewed advisory GHSA-j8g8-j7fc-43v6 lists affected ranges: npm flowise >=0 <=3.0.12)

Commands are suggestions: review each one before running it.