Mac OS X Server NeST -target Buffer Overflow Vulnerability

iDEFENSE Security Advisory 05.03.05:
http://www.idefense.com/application/poi/display?id=239&type=vulnerabilit
ies
May 03, 2005

I. BACKGROUND

Mac OS X is an advanced operating system which blends features of UNIX 
with the ease-of-use of the Macintosh. NetInfo is Darwin's built-in 
directory system. It stores administrative information in a 
hierarchical database of nodes called directories. NeST is the NetInfo
Setup Tool. More information is available on the vendor's website:

    http://www.apple.com

II. DESCRIPTION

Local exploitation of a buffer overflow vulnerability in Apple 
Computer, Inc.'s Mac OS X Server default install allows attackers to 
execute arbitrary code. NeST is the NetInfo Setup Tool for Mac OS X. 
The vulnerability specifically exists due to insufficient bounds 
checking on the argument passed to the '-target' command line 
parameter. Local attackers can supply an overly long value to overflow 
the buffer and execute arbitrary code. The following example debugger
session shows execution control when overflowing the target buffer:

    osx-dev:~ $ gdb -q /usr/sbin/NeST
    (gdb) run -target `perl -e 'print "\xbf\xff\xfe\xe4" x 800 '`
    
    Starting program: /usr/sbin/NeST -target `perl -e 'print 
       "\xbf\xff\xfe\xe4" x 800 '`
    Reading symbols for shared libraries ............... done
    Password:
    1976-04-01 08:29:04.480 NeST[3359] CFLog (0):
            CFPropertyListCreateFromXMLData(): plist parse failed; the
               data is not proper UTF-8. The file name for this data
               could be:
            Info.plist -- file://localhost/usr/sbin/
            The parser will retry as in 10.2, but the problem should be
               corrected in the plist.
    
    Program received signal EXC_BAD_INSTRUCTION, Illegal
       instruction/operand.
    0xbffffee8 in ?? ()
    
    (gdb) bt
    #0  0xbffffee8 in ?? ()
    #1  0xbffffee4 in ?? () 

III. ANALYSIS

Successful exploitation of this vulnerability will result in execution 
of arbitrary code with root privileges. The vulnerability itself is a 
textbook stack overflow and is trivially exploitable. This binary does 
not ship by default with the standard install of Mac OS X, so only OS X 
Server platforms are affected.

IV. DETECTION

iDEFENSE has confirmed that Apple Computer, Inc.'s Mac OS X Server 
10.3.7 is vulnerable. All versions of OS X Server are suspected to be 
vulnerable.
  
V. WORKAROUND

As a workaround solution, remove the setuid bit from the NeST binary 
until the vendor releases a patch.

VI. VENDOR RESPONSE

The vulnerability is addressed in Apple Security Update 2005-005:

    http://docs.info.apple.com/article.html?artnum=301528

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
names CAN-2005-0594 to these issues. This is a candidate for inclusion
in the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

02/28/2005  Initial vendor notification
02/28/2005  Initial vendor response
05/03/2005  Coordinated public disclosure

IX. CREDIT

Nico is credited with this discovery.

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X. LEGAL NOTICES

Copyright (c) 2005 iDEFENSE, Inc.

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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.