"Successful su for user by root" - suspicious entries in my /var/log/auth.log?

security authentication logs su viruses

This post on reddit made me go through my logs. That's when I discovered the following entries which appeared on two non-subsequent days. "user" is my user account.

Aug  4 22:50:37 UbuntuSystem sudo: pam_unix(sudo:session): session opened for user root by user(uid=1000)
Aug  4 22:50:39 UbuntuSystem sudo: pam_unix(sudo:session): session closed for user root
Aug  4 22:51:16 UbuntuSystem su[10710]: Successful su for user by root
Aug  4 22:51:16 UbuntuSystem su[10710]: + ??? root:user
Aug  4 22:51:16 UbuntuSystem su[10710]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 22:51:17 UbuntuSystem su[10710]: pam_unix(su:session): session closed for user user
Aug  4 22:51:17 UbuntuSystem su[10720]: Successful su for user by root
Aug  4 22:51:17 UbuntuSystem su[10720]: + ??? root:user
Aug  4 22:51:17 UbuntuSystem su[10720]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 22:51:17 UbuntuSystem su[10720]: pam_unix(su:session): session closed for user user
Aug  4 22:51:17 UbuntuSystem su[10735]: Successful su for user by root
Aug  4 22:51:17 UbuntuSystem su[10735]: + ??? root:user
Aug  4 22:51:17 UbuntuSystem su[10735]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 22:51:17 UbuntuSystem su[10735]: pam_unix(su:session): session closed for user user
Aug  4 22:51:17 UbuntuSystem su[10763]: Successful su for user by root
Aug  4 22:51:17 UbuntuSystem su[10763]: + ??? root:user
Aug  4 22:51:17 UbuntuSystem su[10763]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 22:51:17 UbuntuSystem su[10763]: pam_unix(su:session): session closed for user user
Aug  4 22:51:17 UbuntuSystem su[10773]: Successful su for user by root
Aug  4 22:51:17 UbuntuSystem su[10773]: + ??? root:user
Aug  4 22:51:17 UbuntuSystem su[10773]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 22:51:17 UbuntuSystem su[10773]: pam_unix(su:session): session closed for user user
Aug  4 22:51:17 UbuntuSystem su[10788]: Successful su for user by root
Aug  4 22:51:17 UbuntuSystem su[10788]: + ??? root:user
Aug  4 22:51:17 UbuntuSystem su[10788]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 22:51:17 UbuntuSystem su[10788]: pam_unix(su:session): session closed for user user
Aug  4 22:51:17 UbuntuSystem su[10801]: Successful su for user by root
Aug  4 22:51:17 UbuntuSystem su[10801]: + ??? root:user
Aug  4 22:51:17 UbuntuSystem su[10801]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 22:51:17 UbuntuSystem su[10801]: pam_unix(su:session): session closed for user user
Aug  4 22:51:17 UbuntuSystem su[10814]: Successful su for user by root
Aug  4 22:51:17 UbuntuSystem su[10814]: + ??? root:user
Aug  4 22:51:17 UbuntuSystem su[10814]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 22:51:17 UbuntuSystem su[10814]: pam_unix(su:session): session closed for user user
Aug  4 22:51:17 UbuntuSystem su[10829]: Successful su for user by root
Aug  4 22:51:17 UbuntuSystem su[10829]: + ??? root:user
Aug  4 22:51:17 UbuntuSystem su[10829]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 22:51:17 UbuntuSystem su[10829]: pam_unix(su:session): session closed for user user
Aug  4 22:51:17 UbuntuSystem su[10842]: Successful su for user by root
Aug  4 22:51:17 UbuntuSystem su[10842]: + ??? root:user
Aug  4 22:51:17 UbuntuSystem su[10842]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 22:51:17 UbuntuSystem su[10842]: pam_unix(su:session): session closed for user user
Aug  4 22:51:17 UbuntuSystem su[10855]: Successful su for user by root
Aug  4 22:51:17 UbuntuSystem su[10855]: + ??? root:user
Aug  4 22:51:17 UbuntuSystem su[10855]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 22:51:17 UbuntuSystem su[10855]: pam_unix(su:session): session closed for user user
Aug  4 23:41:39 UbuntuSystem su[11153]: Successful su for user by root
Aug  4 23:41:39 UbuntuSystem su[11153]: + ??? root:user
Aug  4 23:41:39 UbuntuSystem su[11153]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 23:41:39 UbuntuSystem su[11153]: pam_unix(su:session): session closed for user user
Aug  4 23:41:39 UbuntuSystem su[11166]: Successful su for user by root
Aug  4 23:41:39 UbuntuSystem su[11166]: + ??? root:user
Aug  4 23:41:39 UbuntuSystem su[11166]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 23:41:39 UbuntuSystem su[11166]: pam_unix(su:session): session closed for user user
Aug  4 23:41:39 UbuntuSystem su[11181]: Successful su for user by root
Aug  4 23:41:39 UbuntuSystem su[11181]: + ??? root:user
Aug  4 23:41:39 UbuntuSystem su[11181]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 23:41:39 UbuntuSystem su[11181]: pam_unix(su:session): session closed for user user
Aug  4 23:41:39 UbuntuSystem su[11193]: Successful su for user by root
Aug  4 23:41:39 UbuntuSystem su[11193]: + ??? root:user
Aug  4 23:41:39 UbuntuSystem su[11193]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 23:41:39 UbuntuSystem su[11193]: pam_unix(su:session): session closed for user user
Aug  4 23:41:39 UbuntuSystem su[11211]: Successful su for user by root
Aug  4 23:41:39 UbuntuSystem su[11211]: + ??? root:user
Aug  4 23:41:39 UbuntuSystem su[11211]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 23:41:39 UbuntuSystem su[11211]: pam_unix(su:session): session closed for user user
Aug  4 23:41:39 UbuntuSystem su[11226]: Successful su for user by root
Aug  4 23:41:39 UbuntuSystem su[11226]: + ??? root:user
Aug  4 23:41:39 UbuntuSystem su[11226]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 23:41:39 UbuntuSystem su[11226]: pam_unix(su:session): session closed for user user
Aug  4 23:41:39 UbuntuSystem su[11241]: Successful su for user by root
Aug  4 23:41:39 UbuntuSystem su[11241]: + ??? root:user
Aug  4 23:41:39 UbuntuSystem su[11241]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 23:41:39 UbuntuSystem su[11241]: pam_unix(su:session): session closed for user user
Aug  4 23:41:39 UbuntuSystem su[11253]: Successful su for user by root
Aug  4 23:41:39 UbuntuSystem su[11253]: + ??? root:user
Aug  4 23:41:39 UbuntuSystem su[11253]: pam_unix(su:session): session opened for user user by (uid=0)
Aug  4 23:41:39 UbuntuSystem su[11253]: pam_unix(su:session): session closed for user user
Aug  4 23:42:18 UbuntuSystem gnome-screensaver-dialog: gkr-pam: unlocked login keyring
Aug  4 23:42:33 UbuntuSystem polkitd(authority=local): Unregistered Authentication Agent for unix-session:/org/freedesktop/ConsoleKit/Session2 (system bus name :1.48, object path /org/gnome/PolicyKit1/AuthenticationAgent, locale en_US.UTF-8) (disconnected from bus)

Aug 15 20:17:01 UbuntuSystem CRON[26579]: pam_unix(cron:session): session opened for user root by (uid=0)
Aug 15 20:17:01 UbuntuSystem CRON[26579]: pam_unix(cron:session): session closed for user root
Aug 15 21:15:15 UbuntuSystem su[27098]: Successful su for user by root
Aug 15 21:15:15 UbuntuSystem su[27098]: + ??? root:user
Aug 15 21:15:15 UbuntuSystem su[27098]: pam_unix(su:session): session opened for user user by (uid=0)
Aug 15 21:15:15 UbuntuSystem su[27098]: pam_unix(su:session): session closed for user user
Aug 15 21:17:01 UbuntuSystem CRON[27141]: pam_unix(cron:session): session opened for user root by (uid=0)
Aug 15 21:17:01 UbuntuSystem CRON[27141]: pam_unix(cron:session): session closed for user root

Apart from these iterations the only other times I found a similar output was when trying out the guest account:

Aug 11 22:38:49 UbuntuSystem lightdm: pam_unix(lightdm:session): session closed for user lightdm
Aug 11 22:38:49 UbuntuSystem groupadd[2918]: group added to /etc/group: name=guest-4Eflre, GID=125
Aug 11 22:38:49 UbuntuSystem groupadd[2918]: group added to /etc/gshadow: name=guest-4Eflre
Aug 11 22:38:49 UbuntuSystem groupadd[2918]: new group: name=guest-4Eflre, GID=125
Aug 11 22:38:50 UbuntuSystem useradd[2922]: new user: name=guest-4Eflre, UID=115, GID=125, home=/, shell=/bin/bash
Aug 11 22:38:50 UbuntuSystem usermod[2927]: change user 'guest-4Eflre' password
Aug 11 22:38:50 UbuntuSystem chage[2932]: changed password expiry for guest-4Eflre
Aug 11 22:38:50 UbuntuSystem chfn[2935]: changed user 'guest-4Eflre' information
Aug 11 22:38:50 UbuntuSystem usermod[2943]: change user 'guest-4Eflre' home from '/' to '/tmp/guest-4Eflre'
Aug 11 22:38:50 UbuntuSystem su[2948]: Successful su for guest-4Eflre by root
Aug 11 22:38:50 UbuntuSystem su[2948]: + ??? root:guest-4Eflre
Aug 11 22:38:50 UbuntuSystem su[2948]: pam_unix(su:session): session opened for user guest-4Eflre by (uid=0)
Aug 11 22:38:50 UbuntuSystem su[2948]: pam_unix(su:session): session closed for user guest-4Eflre
Aug 11 22:38:50 UbuntuSystem lightdm: pam_unix(lightdm-autologin:session): session opened for user guest-4Eflre by (uid=0)
Aug 11 22:38:50 UbuntuSystem lightdm: pam_ck_connector(lightdm-autologin:session): nox11 mode, ignoring PAM_TTY :0

I might have to add that I set up my system only fairly recently (Aug 4).

Is this behaviour normal? What exactly is going on with all the su commands? Do I have to be worried that my system might be compromised?

Many thanks in advance.


Solution 1:

Those warnings are when you switch from root to your user.

It doesn't appear that you have any problem.

Solution 2:

These are not from when you run sudo. But they are not a problem, either.

The messages say:

Successful su for user by root

This happens whenever you log in. Whether you're logging in as a real user or as a guest user, the login screen runs as root, so it must change user identity from root to a non-root user as part of the login process.

This isn't user becoming root. This is root becoming user.

Related

How to get lock screen option in Lubuntu?
What's the best way to search my file system on ubuntu with instant results?
I cannot play some WMA files
Applications to make photo collages
Ubuntu 12.10 - network manager not listing wireless networks
How to analyze a "[Waiting for headers]" problem during "apt-get update"?
Open all files containing certain text
Symfony2 cache permissions issue ubuntu 12.10
wlan and macchanger
Text editor where unsaved files can be recovered after computer crash?
export http_proxy: where does the proxy setting get stored?
bash: ./install.sh: Permission denied installing intel fortran 2011