Restrict service account from direct interactive sessions Post: 303024303

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Top Forums UNIX for Advanced & Expert Users Restrict service account from direct interactive sessions Post 303024303 by bgstack15 on Friday 5th of October 2018 03:51:06 PM

10-05-2018

Registered User

I started a possible tool to watch the logs and deal with shell sessions, but it can be easily defeated with a ssh remoteserver /bin/bash.

Code:

#!/bin/sh
# startdate: 2018-10-05 13:20
# Purpose: if a service account user logs in interactively, then kill it.
# incomplete. Can be foiled with: ssh -t clonetest210 /bin/bash
# improve: how to retrieve log entries to check

# Sample journalctl output.
# Oct 05 13:12:52 clonetest210 sshd[1868]: Starting session: shell on pts/3 for bgstack15-local from 10.200.18.240 port 59349 id 0

# Dependencies: sshd_config LogLevel VERBOSE
# journalctl -f -u sshd is not sufficient. I cannot tell what unit logs the notice seen above.

BADUSERS="(bgstack15-local|prophetess)"

journalctl -n100 | grep -oE "sshd\[.{1,10}\]: Starting session: shell on .* for ${BADUSERS} from .*" | awk '{print $1,$6,$8,$10}' | while read longpid tty tu srcip ;
do
   pid="$( echo "${longpid}" | tr -dc "[:digit:]" )"
   echo "Found login: ${tu} from pid ${pid} from ip ${srcip} and made terminal ${tty}"

   # investigate that current pid. if it exists and is sshd, kill it
   psout="$( ps -e -o pid:9,ppid:9,user:15,command:90 2>/dev/null | awk "\$1 == $pid" )"
   if test -n "${psout}" && echo "${psout}" | grep -qE "sshd:" ;
   then
      echo "need to warn user ${tu} on tty ${tty} and then kill pid ${pid}"
      printf "\n%s\n" "Interactive sessions are not allowed for user ${tu}." > "/dev/${tty}"
      sleep 0
      kill "${pid}"
   fi
done

bgstack15

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LEARN ABOUT LINUX

pam_deny

PAM_DENY(8)							 Linux-PAM Manual						       PAM_DENY(8)

NAME

       pam_deny - The locking-out PAM module

SYNOPSIS

       pam_deny.so

DESCRIPTION

       This module can be used to deny access. It always indicates a failure to the application through the PAM framework. It might be suitable
       for using for default (the OTHER) entries.

OPTIONS

       This module does not recognise any options.

MODULE TYPES PROVIDED

       All module types (account, auth, password and session) are provided.

RETURN VALUES

       PAM_AUTH_ERR
	   This is returned by the account and auth services.

       PAM_CRED_ERR
	   This is returned by the setcred function.

       PAM_AUTHTOK_ERR
	   This is returned by the password service.

       PAM_SESSION_ERR
	   This is returned by the session service.

EXAMPLES

	   #%PAM-1.0
	   #
	   # If we don't have config entries for a service, the
	   # OTHER entries are used. To be secure, warn and deny
	   # access to everything.
	   other auth	  required	 pam_warn.so
	   other auth	  required	 pam_deny.so
	   other account  required	 pam_warn.so
	   other account  required	 pam_deny.so
	   other password required	 pam_warn.so
	   other password required	 pam_deny.so
	   other session  required	 pam_warn.so
	   other session  required	 pam_deny.so

SEE ALSO

       pam.conf(5), pam.d(5), pam(7)

AUTHOR

       pam_deny was written by Andrew G. Morgan <morgan@kernel.org>

Linux-PAM Manual						    06/04/2011							       PAM_DENY(8)