Attack Chain

1. An attacker authenticates to the FlowiseAI application using valid credentials or a valid API key.
2. The attacker crafts a malicious JavaScript payload designed to escape the NodeVM sandbox.
3. The attacker sends an HTTP POST request to the /api/v1/node-custom-function endpoint, including the malicious JavaScript code in the javascriptFunction parameter within the request body.
4. The server, lacking proper authorization checks, executes the attacker-supplied JavaScript code within the Custom JS Function node.
5. The malicious JavaScript exploits an exception path within the NodeVM to escape the sandbox, gaining access to the host’s process object and child_process module.
6. The attacker uses the child_process module to execute arbitrary system commands on the Flowise server. For example, cp.execSync('id').toString().trim() to get the user ID.
7. The attacker retrieves the output of the executed command and potentially uses it to gather sensitive information or further compromise the system.
8. The attacker leverages the compromised server for lateral movement, data exfiltration, or other malicious activities.

Impact

Successful exploitation allows any authenticated Flowise user to execute arbitrary commands on the Flowise server. This can lead to a full compromise of the server, including the ability to read environment variables and secrets, access the filesystem, and make outbound network requests. The default configuration, which relies on the vulnerable NodeVM sandbox when E2B_APIKEY is not configured, increases the attack surface, as the majority of self-hosted Flowise instances are likely affected. A successful attack can result in data breaches, service disruption, and further exploitation of the compromised environment.

Recommendation

• Deploy the “FlowiseAI NodeVM Sandbox Escape Attempt” Sigma rule to detect attempts to exploit this vulnerability by identifying the use of the Error object and constructor chain manipulation within the Custom JS Function node.
• Deploy the “FlowiseAI Custom Function RCE via API” Sigma rule to detect HTTP requests to the /api/v1/node-custom-function endpoint with suspicious JavaScript payloads containing potentially malicious code execution patterns.
• Immediately apply the recommended remediation steps: add explicit permission gating to /api/v1/node-custom-function, fail closed if E2B_APIKEY is absent, and restrict this endpoint from generic API key access.