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SECURITY ADVISORY INTEXXIA(c)
27 11 2001 ID #1048-261101
________________________________________________________________________
TITLE : libgtop_daemon Remote Format String Vulnerability
CREDITS : Guillaume Pelat / INTEXXIA
________________________________________________________________________

SYSTEM AFFECTED
===============

        libgtop_daemon <= 1.0.12

________________________________________________________________________

DESCRIPTION
===========

        The Laboratory intexxia found a remote exploitable format string
vulnerability in libgtop_daemon which could cause privilege escalation
on a remote system.

________________________________________________________________________

DETAILS
=======

        libgtop_daemon is a GNOME daemon used to monitor process running
on a remote system.

        The Laboratory intexxia just found a remote format string
vulnerability in this daemon. The 2 functions named syslog_message() and
syslog_io_message() are called with a format string which is initialized
by the client.

        By sending a specially crafted format string to the server, it
is possible for a remote attacker to execute arbitrary code on the
remote system with the daemon permissions. This vulnerability could
cause privilege escalation.

        The permitted() function, that verifies if the client trying to
to connect is authorized to, is concerned by this flaw.

        The libgtop_daemon daemon is launched with 'nobody' permissions
by default. Complete exploitation of this vulnerability will permit an
attacker to execute code with the 'nobody' permissions. But this flaw
could be used to compromize the local system by exploiting other local
vulnerabilities.

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PROOF OF CONCEPT
================

        Here is a proof of concept to show where the problem occurs :

Client side :
~ % telnet 127.0.0.1 42800
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
%p%p
Connection closed by foreign host.
~ % telnet 127.0.0.1 42800
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
%n%n
Connection closed by foreign host.

Server side :
~/# libgtop_daemon -f
' from clientn[3877]: Invalid authentication protocol
'0xbffff46c0x804b2ae
libgtop-daemon[3877]: Refused connection from 127.0.0.1.
Segmentation fault

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WORKAROUND
==========

        Although there is an official solution, here is the way to patch
the sources to resolve this problem. The file 'src/daemon/gnuserv.c'
must be modified :

In function syslog_message(), replace :
  syslog (priority, buffer);
by :
  syslog (priority, "%s", buffer);

And in function syslog_io_message(), replace :
  syslog (priority, buffer2);
by :
  syslog (priority, "%s", buffer2);

The Laboratory intexxia developped the following patch to correct this
vulnerability. However, the simplest and probably the best way to
resolve this issue is to install the new version at the above link in
the solution section :

  diff -dru libgtop-1.0.12/src/daemon/gnuserv.c
  libgtop-1.0.12-patched/src/daemon/gnuserv.c
  --- libgtop-1.0.12/src/daemon/gnuserv.c Mon Nov 26 13:48:14 2001
  +++ libgtop-1.0.12-patched/src/daemon/gnuserv.c Mon Nov 26 13:49:26 2001
   -93,7 +93,7
       vsnprintf (buffer, BUFSIZ-1, format, ap);
       va_end (ap);

  - syslog (priority, buffer);
  + syslog (priority, "%s", buffer);
   }
 
   void
   -108,7 +108,7
       va_end (ap);

       snprintf (buffer2, BUFSIZ-1, "%s: %s", buffer, strerror (errno));
  - syslog (priority, buffer2);
  + syslog (priority, "%s", buffer2);
   }
 
   /*

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SOLUTION
========

        There is an official solution now. libgtop_daemon release 1.0.13
has been made to correct this issue. Here is a link where you can
download it :

ftp://ftp.gnome.org/pub/GNOME/stable/sources/libgtop/libgtop-1.0.13.tar.gz

________________________________________________________________________

VENDOR STATUS
=============

        26-11-2001 : This bulletin was sent to the libgtop_daemon
                     developpment team.
        27-11-2001 : The libgtop_daemon developpement team released a
                     new version including the patch for this issue.

________________________________________________________________________

DISCLAIMER
==========

        intexxia provides these informations as a public service and "as
is". Intexxia will not be held accountable for any damage or distress
caused by the proper or improper usage of these materials.

________________________________________________________________________

DIFFUSION CRITERIA
==================

        (c) intexxia 2001. This document is property of intexxia. Feel
free to use and distribute this material as long as credit is given to
intexxia and the author.

________________________________________________________________________

CONTACT
=======

CERT intexxia certintexxia.com
INTEXXIA http://www.intexxia.com
171, av. Georges Clemenceau Standard : +33 1 55 69 49 10
92024 Nanterre Cedex - France Fax : +33 1 55 69 78 80

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