ULTRIX 4.4 dxterm file linking hole

Description:dxterm, which is suid root, allows the user to specify a file to log output too. Unfortunately it will follow a hardlink to append your stuff to files you shouldn't be able to write to.
Author:Trevor Schroeder <tschroed@CHEETAH.WSC.EDU>
Compromise: root (local)
Vulnerable Systems:Ultrix 4.4, probably 4.5
Date:26 June 1997

Date: Thu, 26 Jun 1997 10:16:05 -0500
From: Trevor Schroeder <tschroed@CHEETAH.WSC.EDU>
Subject: Problem in dxterm (ULTRIX)

On ULTRIX 4.4 (most likely 4.5 as well), there's an enhanced xterm called
dxterm.  Normally it's setuid (doh!).  dxterm allows users to select a file to
log output to.  It's a trivial matter to link this file to another file and
since dxterm is running as root, it's very easy to append arbitrary data to
any file on the filesystem, even if not owned by the particular user.  It does
not seem to follow symlinks.

"...because this little girl needs stuff."

Trevor Schroeder                    tschroed@cheetah.wsc.edu

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