Escobar

This is an alternative to cntlm utility, but written in Go. It's aim to be simpler and easier to customize for own needs. Mainly tested against McAfee Web Gateway. Tested in Linux, macOS and Windows, but should work on other OS like Android.

Unlike cntlm it uses Kerberos-based authorization. It also supports Basic Authorization (as dedicated mode), this is useful while KDC is unavailable (e.g. while using VPN).

As an extra feature it deploys small static server with two routes:

1. GET /proxy.pac — simple PAC-file (Proxy Auto-Configuration).
2. GET /ca.crt — always actual root certificate. Useful during first setup to retrieve Man-In-The-Middle root certificate (corporate proxy in our case) and add it as trusted.

Testing

Project uses monkey patching, so to test it you need to turn off inlining:

go test -gcflags=-l ./...

As service

Escobar could work as service as well. At first, you need to install it.

sudo escobar -d http://proxy.evil.corp:9090/ --install

After installing service, it will create config file from CLI parameters:

Windows	Linux/BSD	macOS
%PROGRAMDATA%\Escobar\Escobar\settings.json	${XDG_CONFIG_DIRS}/etc/xdg/Escobar/Escobar/settings.json	/Library/Application Support/Escobar/Escobar/settings.json

settings.json file example:

{
	"proxy": {
		"addr": "localhost:3128",
		"downstreamProxyURL": "http://proxy.evil.corp:9090/",
                "downstreamProxyDialRetries": 0,
		"downstreamProxyAuth": {
			"user": "",
			"password": "",
			"keytab": ""
		},
		"kerberos": {
			"realm": "",
			"kdc": ""
		},
		"timeouts": {
			"server": {
				"readTimeout": 0,
				"readHeaderTimeout": 30000000000,
				"writeTimeout": 0,
				"idleTimeout": 60000000000
			},
			"client": {
				"readTimeout": 0,
				"writeTimeout": 0,
				"keepAlivePeriod": 60000000000
			},
			"downstreamProxy": {
				"dialTimeout": 10000000000,
				"readTimeout": 0,
				"writeTimeout": 0,
				"keepAlivePeriod": 60000000000
			}
		},
		"pingURL": "https://www.google.com/",
		"mode": "auto"
	},
	"static": {
		"addr": "localhost:3129"
	},
	"useSystemLogger": true,
	"verbose": [
		true
	]
}

Status

This app provides as is and proper work could not be guaranteed. You are free to contribute by creating issues and PR.

Using

Run escobar --help to get this detailed help:

Usage:
  escobar [OPTIONS]

Application Options:
  /l, /syslog                                                     Enable system logger (syslog or Windows Event Log)
      /install                                                    Install service
      /uninstall                                                  Uninstall service
  /v, /verbose                                                    Verbose logs [%ESCOBAR_VERBOSE%]
  /V, /version                                                    Escobar version

Proxy args:
  /a, /proxy.addr:                                                Proxy address (default: localhost:3128) [%ESCOBAR_PROXY_ADDR%]
  /d, /proxy.downstream-proxy-url:http://proxy.evil.corp:9090     Downstream proxy URL [%ESCOBAR_PROXY_DOWNSTREAM_PROXY_URL%]
  /r, /proxy.downstream-proxy-dial-retries:0                      Downstream proxy dial retries (default: 0) [%ESCOBAR_PROXY_DOWNSTREAM_PROXY_DIAL_RETRIES%]
      /proxy.ping-url:                                            URL to ping anc check credentials validity (default: https://www.google.com/) [%ESCOBAR_PROXY_PING_URL%]
  /m, /proxy.mode:                                                Escobar mode (default: auto) [%ESCOBAR_PROXY_MODE%]

Downstream Proxy authentication:
  /u, /proxy.downstream-proxy-auth.user:                          Downstream Proxy user [%ESCOBAR_PROXY_DOWNSTREAM_PROXY_AUTH_USER%]
  /p, /proxy.downstream-proxy-auth.password:                      Downstream Proxy password [%ESCOBAR_PROXY_DOWNSTREAM_PROXY_AUTH_PASSWORD%]
  /k, /proxy.downstream-proxy-auth.keytab:                        Downstream Proxy path to keytab-file [%ESCOBAR_PROXY_DOWNSTREAM_PROXY_AUTH_KEYTAB%]

Kerberos options:
      /proxy.kerberos.realm:EVIL.CORP                             Kerberos realm [%ESCOBAR_PROXY_KERBEROS_REALM%]
      /proxy.kerberos.kdc:kdc.evil.corp:88                        Key Distribution Center (KDC) address [%ESCOBAR_PROXY_KERBEROS_KDC%]

Server timeouts:
      /proxy.timeouts.server.read:                                HTTP server read timeout (default: 0s) [%ESCOBAR_PROXY_TIMEOUTS_SERVER_READ%]
      /proxy.timeouts.server.read-header:                         HTTP server read header timeout (default: 30s) [%ESCOBAR_PROXY_TIMEOUTS_SERVER_READ_HEADER%]
      /proxy.timeouts.server.write:                               HTTP server write timeout (default: 0s) [%ESCOBAR_PROXY_TIMEOUTS_SERVER_WRITE%]
      /proxy.timeouts.server.idle:                                HTTP server idle timeout (default: 1m) [%ESCOBAR_PROXY_TIMEOUTS_SERVER_IDLE%]

Client timeouts:
      /proxy.timeouts.client.read:                                Client read timeout (default: 0s) [%ESCOBAR_PROXY_TIMEOUTS_CLIENT_READ%]
      /proxy.timeouts.client.write:                               Client write timeout (default: 0s) [%ESCOBAR_PROXY_TIMEOUTS_CLIENT_WRITE%]
      /proxy.timeouts.client.keepalive-period:                    Client keepalive period (default: 1m) [%ESCOBAR_PROXY_TIMEOUTS_CLIENT_KEEPALIVE_PERIOD%]

Downstream Proxy timeouts:
      /proxy.timeouts.downstream.dial:                            Downstream proxy dial timeout (default: 10s) [%ESCOBAR_PROXY_TIMEOUTS_DOWNSTREAM_DIAL%]
      /proxy.timeouts.downstream.read:                            Downstream proxy read timeout (default: 0s) [%ESCOBAR_PROXY_TIMEOUTS_DOWNSTREAM_READ%]
      /proxy.timeouts.downstream.write:                           Downstream proxy write timeout (default: 0s) [%ESCOBAR_PROXY_TIMEOUTS_DOWNSTREAM_WRITE%]
      /proxy.timeouts.downstream.keepalive-period:                Downstream proxy keepalive period (default: 1m) [%ESCOBAR_PROXY_TIMEOUTS_DOWNSTREAM_KEEPALIVE_PERIOD%]

Static args:
      /static.addr:                                               Static server address (default: localhost:3129) [%ESCOBAR_STATIC_ADDR%]

Help Options:
  /?                                                              Show this help message
  /h, /help                                                       Show this help message

Keytab-file support

Buy default I recommend to use auto mode that use Windows SSPI or Linux ccache. But you could also use manual mode to pass keytab-files instead of passing plain password. It's safer and less accessible. Below you can read about recommended setup.

1. Create service user escobar and lock it:

   # useradd -M escobar
   # usermod -L escobar

2. Create escobar directory inside /etc and give escobar user proper rights:

   # mkdir /etc/escobar
   # chown escobar:escobar /etc/escobar
   # chmod 0700 /etc/escobar

3. Create proper keytab-file by using ktutil utility:

   $ sudo -u escobar ktutil
   ktutil: add_entry -password -p ivanovii@EVIL.CORP -k 0 -e aes256-cts-hmac-sha1-96
   Password for ivanovii@EVIL.CORP:
   ktutil: write_kt /etc/escobar/ivanovii.keytab
   ktutil: exit

Keytab-file troubleshooting

• Check rights:
  • Directory should have 0700.
  • Keytab-file itself 0600.
  • Both directory and keytab should be owned by user who execute software.
• Check principal name. Usually it's your username and realm: username@REALM.COM
• Check KVNO, it could be invalid. Everytime you change your password, KVNO updates by rule Current KVNO + 1.
• Check encryption type. In example guide above I showed how to generate keytab-file with aes256-cts-hmac-sha1-96. But in your case it could be another cipher.

In case of principal name, KVNO and encryption type program should print what does it looking for.