GHSA-j8g8-j7fc-43v6 Flowise has Arbitrary File Upload via MIME Spoofing
Vulnerability **Description****Vulnerability Overview**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).**Vulnerable Code**Upload Route Definitionhttps://github.com/FlowiseAI/Flowise/blob/d17c4394a238b49327b493c89feee45f3a20bb91/packages/server/src/routes/attachments/index.ts#L7-L10Mount /api/v1/attachments to the global routerhttps://github.com/FlowiseAI/Flowise/blob/d17c4394a238b49327b493c89feee45f3a20bb91/packages/server/src/routes/index.ts#L72-L77Include /api/v1/attachments in the WHITELIST_URLS listhttps://github.com/FlowiseAI/Flowise/blob/d17c4394a238b49327b493c89feee45f3a20bb91/packages/server/src/utils/constants.ts#L6-L26Bypass JWT validation if the URL is whitelistedhttps://github.com/FlowiseAI/Flowise/blob/d17c4394a238b49327b493c89feee45f3a20bb91/packages/server/src/index.ts#L213-L228Multer Configuration: Saves files without file type validationhttps://github.com/FlowiseAI/Flowise/blob/d17c4394a238b49327b493c89feee45f3a20bb91/packages/server/src/utils/index.ts#L1917-L1960Transfers uploaded files to storage without verificationhttps://github.com/FlowiseAI/Flowise/blob/d17c4394a238b49327b493c89feee45f3a20bb91/packages/server/src/utils/createAttachment.ts#L124-L158PoC**PoC Description**Create a local file named `shell.js` containing arbitrary JavaScript code (or a malicious payload).Send a `multipart/form-data` request to the `/api/v1/attachments/891f64a2-a26f-4169-b333-905dc96c200a/:chatId` endpoint without any authentication (login, session, or API keys).During the upload, retain the filename as `shell.js` but spoof the `Content-Type` header as `application/pdf`.This exploits the server's reliance solely on the client-provided `file.mimetype`, forcing it to process the malicious JS file as an allowed PDF, thereby confirming unauthenticated arbitrary file upload.**PoC**Impact**1. Root Cause**
The vulnerability stems from relying solely on the MIME type without cross-validating the file extension or actual content. This allows attackers to upload executable files (e.g., `.js`, `.php`) or malicious scripts (`.html`) by masquerading them as benign images or documents.**2. Key Attack Scenarios****Server Compromise (RCE):** An attacker uploads a **Web Shell** and triggers its execution on the server. Successful exploitation grants system privileges, allowing unauthorized access to internal data and full control over the server.**Client-Side Attack (Stored XSS):** An attacker uploads files containing malicious scripts (e.g., HTML, SVG). When a victim views the file, the script executes within their browser, leading to session cookie theft and account takeover.**3. Impact**
This vulnerability is rated as **High** severity. The risk is particularly critical if the system utilizes shared storage (e.g., S3, GCS) or static hosting features, as the compromise could spread to the entire infrastructure and affect other tenants.
CVSS v4.0 score: 8.2