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Old 06-14-2019, 10:26 AM   #1
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Registered: Aug 2018
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LXDM/LXDE Logging Bad Usernames

I am attempting to log instances where a user attempts to log in to Ubuntu 16.04 through the LXDM greeter with a bad username. If the user logs in with a correct username but a bad password, it is currently logged via syslog and audit. However, if they use a bad username, nothing appears in the logs.

If they use the terminal or ssh to attempt to login with a bad username, it IS logged, so this is just isolated to LXDM.

I believe that the lxdm-greeter somehow checks the username before going to PAM... I have put some hooks (via in PAM and they never get executed when the username entered in LXDM is invalid. Additionally, the pam_faildelay module does not operate either... if the LXDM username is bad, they are prompted for a password but there is no delay before being rejected. This makes it easy for someone to guess if username is valid or not.

So my question is... is this true? Does lxdm somehow verify the username before going to PAM? Is there a way to bypass this behavior and let PAM do the checking? And also, more importantly, is there any way to log an authentication failure based on bad username when using the LXDM greeter?


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