bugtraq - Re: Mathematica8.0.4 on Linux /tmp/MathLink vulnerability

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Date: Tue, 17 Apr 2012 06:51:20 +1000
From: paul.szabo@...ney.edu.au
To: dhillonv10@...il.com
Cc: bugtraq@...urityfocus.com, full-disclosure@...ts.grok.org.uk
Subject: Re: Mathematica8.0.4 on Linux /tmp/MathLink vulnerability

Dear Vikram,

>> Mathematica on Linux uses the /tmp/MathLink directory in insecure ways.
>> Mathematica creates or re-uses an existing /tmp/MathLink directory, and
>> overwrites files within and follows symlinks. ...
>
> One quick fix here could be to change user permissions with chmod or
> add a new group where Mathematica in /tmp doesn't have permissions to
> anything under /home so then even if a user is compromised, the
> symlink won't work because the user doesn't have permissions. A root
> user here is an entirely different problem, here an attacker can
> symlink to any directory. So a new group to setup permissions for
> Mathemtica /tmp access would be a better idea. Will look into a patch
> soon.

My ideas for a fix, so far:

It is tempting to add O_NOFOLLOW to the relevant open() calls, maybe by
changing the string "open" to something else:
  perl -i.bak -pe 's/open/PSzO/g' SystemFiles/Libraries/Linux*/libML*.so
and LD_PRELOAD a library built from something like
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <fcntl.h>
  int PSzO(const char *pathname, int flags, mode_t mode)
  {
    return open(pathname, flags|O_NOFOLLOW, mode);
  }
but that would not work: I believe those files in /tmp/MathLink allow
other processes to send commands to the running Mathematica session,
possibly including shell escapes.

The fix might be to make the directory in /tmp private to the user,
naming it /tmp/MathLink-$USER and checking it has right owner and
"chmod 0700" permissions. That fix will need to be implemented by
Wolfram.

Cheers, Paul

Paul Szabo   psz@...hs.usyd.edu.au   http://www.maths.usyd.edu.au/u/psz/
School of Mathematics and Statistics   University of Sydney    Australia