fix localization issue in module linux/gather/ppp_chap_secrets

[pingport80]

Summary

This PR fixes a localization issue in the post module linux/gather/ppp_chat_secrets. The module was using strings like permission denied, empty etc. received from the remote system to verify some checks. But the error messages like these can vary from locale to locale.

Verification Steps

Before

The remote system has a spanish locale so the error message permission denied will be printed as permiso denegado but the module is treating that error message as data and processing it.

msf6 post(linux/gather/pptpd_chap_secrets) > rerun 
[*] Reloading module...

PPTPd chap-secrets
==================

 Client  Server                  Secret   IP
 ------  ------                  ------   --
 cat:    /etc/ppp/chap-secrets:  Permiso  denegado

[+] Secrets stored in: /home/pingport80/.msf4/loot/20210526201321_default_127.0.0.1_linux.chapsecret_194661.txt
[*] Post module execution completed

After

The module fails with an error message if the file /etc/ppp/chat-secrets is not present or not readable.

msf6 post(linux/gather/pptpd_chap_secrets) > rerun 
[*] Reloading module...

[-] Post aborted due to failure: bad-config: The file /etc/ppp/chap-secrets does not exist or is not a readable file!
[*] Post module execution completed
msf6 post(linux/gather/pptpd_chap_secrets) > 

If the file is present and readable it should be working as expected.

msf6 post(linux/gather/pptpd_chap_secrets) > rerun
[*] Reloading module...

PPTPd chap-secrets
==================

 Client   Server   Secret   IP
 ------   ------   ------   --
 client0  server0  secret0  127.0.0.1

[+] Secrets stored in: /home/pingport80/.msf4/loot/20210601220120_default_127.0.0.1_linux.chapsecret_598082.txt
[*] Post module execution completed

[smcintyre-r7]

I was able to reproduce the original bug and confirm that these changes fix it. Thanks!

Testing Output

Original bug

msf6 payload(python/meterpreter/reverse_tcp) > use post/linux/gather/pptpd_chap_secrets 
msf6 post(linux/gather/pptpd_chap_secrets) > show options 

Module options (post/linux/gather/pptpd_chap_secrets):

   Name     Current Setting        Required  Description
   ----     ---------------        --------  -----------
   FILE     /etc/ppp/chap-secrets  yes       The default path for chap-secrets
   SESSION  -1                     yes       The session to run this module on.

msf6 post(linux/gather/pptpd_chap_secrets) > run

[!] SESSION may not be compatible with this module (unloadable Meterpreter extension: )
PPTPd chap-secrets
==================

 Client  Server                  Secret   IP
 ------  ------                  ------   --
 cat:    /etc/ppp/chap-secrets:  Permiso  denegado

[+] Secrets stored in: /home/smcintyre/.msf4/loot/20210604093316_default_192.168.159.128_linux.chapsecret_430998.txt
[*] Post module execution completed
msf6 post(linux/gather/pptpd_chap_secrets) >

Fixed

msf6 payload(python/meterpreter/reverse_tcp) > use post/linux/gather/pptpd_chap_secrets 
msf6 post(linux/gather/pptpd_chap_secrets) > show options 

Module options (post/linux/gather/pptpd_chap_secrets):

   Name     Current Setting        Required  Description
   ----     ---------------        --------  -----------
   FILE     /etc/ppp/chap-secrets  yes       The default path for chap-secrets
   SESSION  -1                     yes       The session to run this module on.

msf6 post(linux/gather/pptpd_chap_secrets) > run

[!] SESSION may not be compatible with this module (unloadable Meterpreter extension: )
[-] Failed to open file: /etc/ppp/chap-secrets: core_channel_open: Operation failed: Python exception: PermissionError
[-] Post aborted due to failure: bad-config: The file /etc/ppp/chap-secrets does not exist or is not a readable file!
[*] Post module execution completed
msf6 post(linux/gather/pptpd_chap_secrets) >

[smcintyre-r7]

Release Notes

This fixes a localization-related issue in the post/linux/gather/pptpd_chap_secrets module. If the file is unreadable, Metasploit would treat the permission denied error as the contents.