CVE-2026-30821 Flowise: Arbitrary File Upload via MIME Spoofing
Attackers can upload malicious files by spoofing MIME types due to lack of content validation, potentially leading to remote code execution or stored XSS.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-30821?
CVE-2026-30821 is a high-severity vulnerability in Flowiseai Flowise, published on 7 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Flowise 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.
Weakness: CWE-434
Which versions are affected by CVE-2026-30821?
2 open source packages ship an affected version, including flowise. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
flowise npm | All versions | 3.0.13 |
flowise npm | All versions | 3.0.13 |
Products include Flowiseai Flowise.
How do I fix CVE-2026-30821?
Upgrade flowise to 3.0.13 or later.
Is CVE-2026-30821 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-30821 exists.
Other vulnerabilities in Flowiseai Flowise
- CVE-2025-71338 Flowise through 2.2.7 - Arbitrary File Write to Remote Code Execution via document-store API
- CVE-2026-40933 Flowise: Authenticated RCE Via MCP Adapters
- CVE-2025-61913 Flowise is vulnerable to arbitrary file read, arbitrary file write
- CVE-2025-59528 Flowise has Remote Code Execution vulnerability
- CVE-2026-52098 Code injection in n/a
Sources
Also known as GHSA-j8g8-j7fc-43v6.