fkie_cve-2026-84319

Nginx UI is a web user interface for the Nginx web server. Prior to 2.4.1, the regular HTTP configuration API rejects restricted Nginx directives such as load_module, js_import, and js_content. However, the MCP configuration interface allows a secondary authenticated user to write and apply equivalent restricted configuration content. This allows the user to load ngx_http_js_module.so, import attacker-controlled JavaScript, reload Nginx, and execute NJS in the Nginx worker context. This issue is fixed in version 2.4.1.

GHSA-5r62-gj48-897x — Nginx UI: MCP configuration tools bypass restricted directive validation and allow secondary authenticated users to exe…

Affected: Go: github.com/0xJacky/Nginx-UI

## Summary

The regular HTTP configuration API rejects restricted Nginx directives such as `load_module`, `js_import`, and `js_content`.

However, the MCP configuration interface allows a secondary authenticated user to write and apply equivalent restricted configuration content. In the lab, this allowed the user to load `ngx_http_js_module.so`, import attacker-controlled JavaScript, reload Nginx, and execute NJS in the Nginx worker context.

This is authenticated and is not OS command execution by itself.

## Affected component

- `/mcp` - `/mcp_message` - MCP tool: `nginx_config_add` - Nginx configuration validation

## Impact

A secondary authenticated user can bypass the restricted directive validation enforced by the HTTP API and execute attacker-controlled NJS inside the Nginx worker context.

This may allow modification of Nginx runtime behavior, including responses, routing, headers, redirects, and request handling.

## Minimal PoC

### Preconditions

- Attacker has a secondary authenticated Nginx UI account. - MCP is enabled. - Nginx has NJS available:

```bash find / -name "ngx_http_js_module.so" 2>/dev/null ```

Observed in the lab:

```text /usr/lib/nginx/modules/ngx_http_js_module.so ```

### 1. HTTP API blocks the restricted config

Request:

```http POST /api/configs Authorization: <SECONDARY_USER_JWT> Content-Type: application/json ```

Body:

```json { "name": "nginx.conf", "base_dir": "", "overwrite": true, "sync_node_ids": [], "content": "load_module…

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fkie_cve-2026-84319

GHSA-5r62-gj48-897x — Nginx UI: MCP configuration tools bypass restricted directive validation and allow secondary authenticated users to exe…