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Category:   Application (Generic)  >   Sudo Vendors:   Miller, Todd C.
(OpenBSD Issues Fix for 2.9 and 3.x) Sudo Utility Has Heap Overflow That May Let Local Users Execute Arbitrary Code with Root Privileges
SecurityTracker Alert ID:  1004166
SecurityTracker URL:  http://securitytracker.com/id/1004166
CVE Reference:   CVE-2002-0184   (Links to External Site)
Updated:  Nov 19 2003
Original Entry Date:  Apr 26 2002
Impact:   Execution of arbitrary code via local system, Root access via local system
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 1.6.5p2 and prior
Description:   A vulnerability has been reported in the sudo utility. A local user may be able to obtain root privileges.

Global InterSec reported an off-by-five heap overflow in 'sudo'. A local user can apparently call sudo with a specially formatted argument for the -p command line option to trigger the overflow. It is reported that sudo may not correctly allocate memory when parsing the '%h' (hostname) or '%u' (username) strings in the argument in some situations. A local user could potentially trigger the overflow and execute arbitrary code with root privileges.

The exact nature of the conditions required to exploit this flaw were not provided. However, it is reported that the compile-time options and the length of the hostname may affect whether the application is vulnerable or not.

Impact:   A local user may be able to execute arbitrary code with root privileges in certain situations.
Solution:   OpenBSD has released patches:

ftp://ftp.openbsd.org/pub/OpenBSD/patches/2.9/common/025_sudo.patch
ftp://ftp.openbsd.org/pub/OpenBSD/patches/3.0/common/020_sudo.patch
ftp://ftp.openbsd.org/pub/OpenBSD/patches/3.1/common/002_sudo.patch

Vendor URL:  www.courtesan.com/sudo/ (Links to External Site)
Cause:   Boundary error
Underlying OS:  UNIX (OpenBSD)
Underlying OS Comments:  2.9, 3.0, 3.1

Message History:   This archive entry is a follow-up to the message listed below.
Apr 25 2002 Sudo Utility Has Heap Overflow That May Let Local Users Execute Arbitrary Code with Root Privileges



 Source Message Contents

Subject:  Potential sudo security hole


Summary:
    A heap corruption bug exists in sudo versions 1.5.7 to 1.6.5p2
    (inclusive).  The problem affects expansion of the "%h" and
    "%u" escape sequences in the prompt.  Due to a bug it is possible
    to craft a prompt such that more bytes are written than have
    been allocated.

    Exploiting heap corruption bugs like this requires fairly
    in-depth knowledge of a system's malloc internals.  This class
    of bug has been exploited with the glibc malloc but not, to my
    knowledge, with the malloc shipped with OpenBSD.  It would be
    foolish, however, to simply assume that it is not exploitable
    on OpenBSD.

Details:
    Sudo expands "%h" and "%u" to the hostname and username
    respectively.  This is done in two steps.  In the first step
    sudo calculates the amount of memory required to hold the
    expanded string.  In the second step it does the actual string
    copying and escape sequence expansion.  The bug occurs because
    a variable used to store the last character seen was not
    re-initialized before the second loop.  Consequently, if the
    last character in the prompt is a '%' and the first character
    is a 'h' or 'u', sudo will mistakenly expand the 'h' or 'u',
    thinking the last character processed was a '%'.  This causes
    the computed length to be too small and the malloced buffer
    will overflow.

Credit:
    This problem was brought to my attention by Global InterSec LLC.
    For more information, see their advisory:
	http://www.globalintersec.com/adv/sudo-2002041701.txt

Patches:
    ftp://ftp.openbsd.org/pub/OpenBSD/patches/2.9/common/025_sudo.patch
    ftp://ftp.openbsd.org/pub/OpenBSD/patches/3.0/common/020_sudo.patch
    ftp://ftp.openbsd.org/pub/OpenBSD/patches/3.1/common/002_sudo.patch

    The patches are already in the 2.9, 3.0 and 3.1 patch branches
    (aka the -stable branches).


 
 


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