Re: Where am I? :)

Giorgos Keramidas wrote:

On 2006-03-04 09:00, Kovesdan Gabor <gabor.kovesdan@xxxxxxxxxxxx> wrote:


Giorgos Keramidas wrote:


On 2006-03-04 00:44, Kovesdan Gabor <gabor.kovesdan@xxxxxxxxxxxx> wrote:


Hello,
look at this:

root@server# w
12:41AM up 82 days, 10:05, 0 users, load averages: 0.00, 0.00, 0.00
USER TTY FROM LOGIN@ IDLE WHAT
root@server#

Where am I? :) I don't know exactly how it happened, but I'll
investigate, I have an idea and I'll report if I find out.


Some programs may tweak wtmp to `hide' users that are actively logged
in. One program that I know can do this is screen(1). Hitting ``^A L''
here, between successive `w' invocations, I can see this:

root@flame:/root# w
2:04AM up 2:10, 1 user, load averages: 0.07, 0.16, 0.19
USER TTY FROM LOGIN@ IDLE WHAT
root@flame:/root# w
2:05AM up 2:11, 2 users, load averages: 0.03, 0.14, 0.17
USER TTY FROM LOGIN@ IDLE WHAT
root pts/0 :0:S.0 2:05AM - w
root@flame:/root#


And what do the other logged in users see?



Only what `w' can see too.



With my method I can completely hide, nobody can see me logged in.



What is your method? I haven't seen any description of how *you* ended
up not being logged in. Are you using screen(1) or another program that
tweaks /var/log/wtmp? Which program? Have you found out why your login
seems record in wtmp was marked as logged out?



Here's my method:

http://www.freebsd.org/cgi/query-pr.cgi?pr=94060

So I think it might be an opportunity to abusing. I'll send a PR soon,
I just wanted to know before if somebody already knows about this
trick.



I don't think this is a bug. The permissions of ``/var/log/wtmp'' are:

$ ls -ld /var/log/wtmp
-rw-r--r-- 1 root wheel - 8052 Mar 4 16:51 /var/log/wtmp

What a bug about this would report is that set-user-id programs, like
screen(1), can do all sorts of nasty things if abused. This isn't
exactly a bug, but common knowledge.

- Giorgos



/bin/login is suid, too. Can't screen and login be modified somehow to take care of this issue?

Gabor Kovesdan
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