OSEC

Neohapsis is currently accepting applications for employment. For more information, please visit our website www.neohapsis.com or email hr@neohapsis.com
Bugtraq archives for 3rd quarter (Jul-Sep) 1996: rwhod buffer overflow

rwhod buffer overflow

David J. Meltzer (davemiss.net)
Wed, 21 Aug 1996 16:38:57 -0400 

There is a remote buffer overflow in the path variable in rwhod.c in the
line: (void) sprintf(path, "whod.%s", wd.wd_hostname);

Although wd_hostname is defined to be only 32 characters, it is read as
part of the wd structure from a remote host through a UDP packet and can
be as large as the remainder of the structure starting at that point.

Through examining the source this appears to be a problem in current
OpenBSD, NetBSD, FreeBSD, and Linux distributions.  Through penetration
testing I have also found this problem present on AIX; I have not examined
other platforms running rwhod and so do not know about their potential
vulnerability.

I have succesfully exploited this remotely to produce undesirable effects
(segfaults and overwriting argv[0] on different OSes), I have not spent
sufficient time on this to determine exactly how/if to compromise root
directly with this overflow, but it is definitely something that should be
corrected.

I would suggest prior to the sprintf line you add something to the effect:
if(strlen(wd.wd_hostname) >= sizeof(wd.wd_hostname)) {
  syslog(LOG_WARNING, "possible hostname overflow attack apparently from %x",
         from.sin_addr);
  continue;
  }

                   Program: /usr/sbin/rwhod
Affected Operating Systems: OpenBSD, NetBSD, FreeBSD, Linux, AIX, others.
                            rwhod must be running on the system
              Requirements: Ability to send UDP packet to target host
       Security Compromise: Possible denial of service, Possible annoyance,
                            Possibly root compromise?
                    Author: Dave M. (davemiss.net)
                  Synopsis: rwhod reads a structure from a udp packet and
                            does not check the hostname member of the
                            structure for being the expected size.


--------------------------------+---------------------
       David J. Meltzer         | Email: davemiss.net
       Systems Engineer         |   Web:   www.iss.net
Internet Security Systems, Inc. |   Fax: (404)252-2427









--------------------------------+---------------------
       David J. Meltzer         | Email: davemiss.net
       Systems Engineer         |   Web:   www.iss.net
Internet Security Systems, Inc. |   Fax: (404)252-2427