full-disclosure - /bin/rm file access vulnerability

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Message-ID: <1104407098.4799.19.camel@linuxjoe2.vitras.de>
From: joerg at eschke.net (Jörg Eschke)
Subject: /bin/rm file access vulnerability

Sure, a user with admin rights is able to access/delete every local
file, regardless of the specific filepermissions.
Your 'exploit' will work with e.g. /bin/cat as well.
But i can't see a vulnerability anyway.

Am i missunderstanding something ?

Am Do, den 30.12.2004 schrieb Lennart Hansen um 2:18:
> /bin/rm file access vulnerability
> 
> Affected Products:
>          /bin/rm (all versions, tested on FreeBSD and linux)
>          (http://www.freebsd.org    http://www.kernel.org)
> 
> Author:
>          Xenzeo (Ablazed, Ultralaser, Lennart A. Hansen)
>          xenzeo at blackhat dot dk
> 
> 
> /bin/rm is a program that removes the named file arguments on unix systems.
> When /bin/rm is called it checks the file's permissions and the id of the user
> trying to remove the file. If the user does not have the required permissions
> to delete the file, /bin/rm will simply reject and exit.
> 
> However, it is possible for a person with admin rights (root) to 
> delete _any_ file
> on the system regardless of who has created it and what it's permissions are.
> 
> Proof of concepts:
> $ touch /home/xenzeo/file
> $ ls -l /home/xenzeo/file
> -rw-r--r--  1 xenzeo none 0 Dec 30  2004 /home/xenzeo/file
> $ id
> uid=1000(xenzeo) gid=513(none) groups=513(none),545(users)
> $ su -c 'rm -f /home/xenzeo/file'
> $ ls -l /home/xenzeo/file
> ls: file: No such file or directory
> 
> #!/usr/bin/perl
> if ($#ARGV != 0) {
> 	die "usage: rm-exploit.pl file\r\n";
> } else {
>     $file = $ARGV[0];
>     print "*** CMD: [ /bin/rm -f $file ]\r\n";
>     print "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\r\n";
>     if ($> == 0) {
>        print "[-] EXECUTING CMD\r\n";
>        system("/bin/rm -f $file");
>        print "[-] DONE\r\n";
>        print "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\r\n";
>        exit();
>     } else {
>        print "[-] EXPLOIT FAILED\r\n";
>        print "[-] YOU ARE NOT ROOT\r\n";
>        print "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\r\n";
>     }
> }
> 
> Vender status:
>          Neither FreeBSD nor Linux developers have been contacted yet!
> 
> -Xenzeo