Nginx UI: Node Secret Credential Exposure via URL Query Parameter

## 1. Vulnerability Summary nginx-ui's `Node.Secret` is a master credential that bypasses all JWT/password authentication for the entire API. The application accepts this credential via a **URL query parameter** (`?node_secret=`), causing it to be recorded in plaintext in HTTP access logs, reverse proxy logs, browser history, and HTTP `Referer` headers. Additionally, the official cluster configuration format embeds node secrets directly into URL query strings stored in `app.ini` and environment variables, creating a systemic credential exposure pattern across the entire cluster deployment model. An attacker who gains read access to any log aggregation system, proxy log, or configuration file can extract the node secret and obtain full, persistent, unauthenticated administrative access to the nginx-ui API — including reading TLS private keys, modifying nginx configurations, and (when chained with Bug #1) achieving OS-level code execution. --- ## 2. Root Cause Analysis ### 2.1 Node Secret Accepted as URL Query Parameter The `getNodeSecret` function reads the credential from the URL query string as a fallback when the `X-Node-Secret` header is absent: [1](#3-0) This function is called in both `AuthRequired()` and `AuthRequiredWS()` middleware, meaning the query parameter bypass works for **all authenticated HTTP and WebSocket endpoints**: [2](#3-1) [3](#3-2) The same pattern is repeated in the WebSocket origin checker, which also reads `node_secret` from the URL: [4](#3-3) ### 2.2 Node Secret Is a Full Authentication Bypass The documentation explicitly states this is by design: [5](#3-4) When the secret matches, the middleware sets the request context to an admin-level init user and calls `c.Next()` — bypassing all JWT validation, session checks, and 2FA: [2](#3-1) ### 2.3 Cluster Configuration Embeds Node Secrets in URLs The official cluster configuration format, documented and used in `app.example.ini`, stores node secrets as URL query parameters: [6](#3-5) The `parseNodeUrl` function extracts the secret from the URL's query string and stores it in the database as the node's `Token` field: [7](#3-6) This means node secrets are embedded in: - `app.ini` on disk (readable by any process with filesystem access) - The `NGINX_UI_CLUSTER_NODE` environment variable (visible in `ps aux`, Docker inspect, Kubernetes pod specs, CI/CD logs) - The SQLite database `nodes` table as the `token` column in plaintext ### 2.4 Node Secret Generation Uses UUID The secret is auto-generated as a UUID v4 if not set: [8](#3-7) UUID v4 has 122 bits of entropy, which is adequate. However, the exposure surface described in this report makes entropy irrelevant — the secret is leaked through operational channels, not brute-forced. --- ## 3. Exposure Surface The following table maps each exposure vector to its source in the codebase: | Vector | How It Happens | Who Can See It | |---|---|---| | **HTTP access logs** | `GET /api/settings?node_secret=xxx` logged by nginx/caddy/apache | Log readers, SIEM operators | | **Application logs** | Gin debug mode logs full request URLs | Server operators, log aggregators | | **Browser history** | Admin uses `?node_secret=` URL directly | Anyone with browser access | | **HTTP Referer header** | Page with `?node_secret=` in URL links to external resource | Third-party servers | | **WebSocket URL logs** | `ws://host/api/ws?node_secret=xxx` logged by proxies | Proxy log readers | | **`app.ini` on disk** | Cluster node URLs contain `node_secret=` | Filesystem readers | | **Environment variables** | `NGINX_UI_CLUSTER_NODE=...&node_secret=...` | `ps aux`, Docker inspect, K8s pod specs | | **CI/CD pipeline logs** | Env vars printed during deployment | CI/CD log viewers | | **Database** | `nodes.token` column stored in plaintext SQLite | DB file readers | --- ## 4. Proof of Concept ### Scenario A: Log-Based Secret Extraction **Step 1 — Attacker gains read access to nginx access logs** (e.g., via a misconfigured log aggregator, a compromised monitoring account, or a separate vulnerability). **Step 2 — Search logs for the pattern:** ```bash grep -oP 'node_secret=[^&\s"]+' /var/log/nginx/access.log # Output: node_secret=a1b2c3d4-e5f6-7890-abcd-ef1234567890 ``` **Step 3 — Use the extracted secret for full API access:** ```http GET /api/settings HTTP/1.1 Host: target:9000 X-Node-Secret: a1b2c3d4-e5f6-7890-abcd-ef1234567890 ``` Response: Full settings JSON including `JwtSecret`, `NodeSecret`, all nginx paths, and all configured credentials. ```http GET /api/nginx/config?filepath=/etc/nginx/nginx.conf HTTP/1.1 Host: target:9000 X-Node-Secret: a1b2c3d4-e5f6-7890-abcd-ef1234567890 ``` Response: Full nginx configuration including any embedded credentials. ### Scenario B: Environment Variable Exposure in Docker/Kubernetes **Step 1 — Attacker reads a Kubernetes pod spec or Docker Compose file:** ```yaml environment: - NGINX_UI_CLUSTER_NODE=http://10.0.0.1:9000?name=node1&node_secret=my-node-secret&enabled=true ``` **Step 2 — Extract the secret from the URL query string.** **Step 3 — Authenticate to the target node:** ```http POST /api/nginx/test HTTP/1.1 Host: 10.0.0.1:9000 X-Node-Secret: my-node-secret ``` The attacker now has full admin access to the cluster node. ### Scenario C: Referer Header Leak to Third-Party **Step 1 — Admin navigates to a page with `?node_secret=` in the URL.** **Step 2 — That page contains a resource (image, script, analytics) from a third-party domain.** **Step 3 — Browser sends:** ```http GET /analytics.js HTTP/1.1 Host: analytics.third-party.com Referer: https://nginx-ui.internal/api/settings?node_secret=a1b2c3d4-... ``` The third-party server receives the node secret in the `Referer` header. --- ## 5. Impact - **Confidentiality:** Full read access to all nginx configurations, TLS private keys, ACME account credentials, database contents, and all settings stored in `app.ini`. - **Integrity:** Full write access to a…