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I've recently ran into a very odd occurrence on one system I'm using. For no apparent reason, my user account was deleted, although the home directory is still there.

I have root access, so I can restore the account, but first, I want to know how this happened, and exactly when. Inspecting the root's .bash_history file and the "last" command gave nothing, and I'm (well, was) the only sudoer on the system.

How would I know when this deletion happened?

The distro is CentOS release 5.4 (Final), if that helps.

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2 Answers 2

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If you're the only sudoer, and the only one with legit access to root, then your server was in all probability cracked. Many (less skilled) crackers will delete or disable root accounts to prevent counteraction. Back up your data and reinstall, or if you are able to do a security audit and find the hole the cracker used, do that.

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This is actually what happened. Someone first gained access as a regular user, then tried to login as several app-level users ("oracle"), and finally managed to login as "dev", which is actually the same user as root (userid 0). –  executor21 Dec 28 '10 at 21:06
    
Thanks for replying back to let everyone know what happened. Its good information for others to see. If your mention of oracle is any indication of what that server does, you need to do a full audit. You should do one anyways and reinstall if possible, auditing your data, scripts, programs, user access, etc. –  deltaray Dec 28 '10 at 22:17
    
One more thing: don't trust the backed-up data unless you audit that, too. A really malicious cracker could play with your Oracle databases. If there's financial or medical data in there, you may have legal obligations to report the possibility of leakage. –  CarlF Dec 29 '10 at 13:33

It really depends on how it was deleted and in relation to other users, but here are a few techniques you can try:

  • See if your user is still listed in passwd. If it isn't, then see if its in a file called passwd-, which is a backup made of passwd. If its in there, then the timestamp on that older file would probably indicate when the account was removed.
  • Its possible that the deletion is in root or some user's .bash_history file and you might be able to tell from the context there when it happened
  • If it was done via sudo or something then it might be in /var/log/messages

That's all I can think of right now. Probably a few other techniques.

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