Internet Standards/CD1.mdf/INET/SCC/9525

Text File | 1995-06-07 | 14.5 KB | 294 lines

**************************************************************************
Security Bulletin 9525                 DISA Defense Communications System
June 7, 1995             Published by: DDN Security Coordination Center
                                      ([e-mail])   1-[phone]

                        DEFENSE  DATA  NETWORK
                          SECURITY  BULLETIN

  The DDN SECURITY BULLETIN is distributed by the DDN SCC (Security
  Coordination Center) under DISA contract as a means of communicating
  information on network and host security exposures, fixes, and concerns
  to security and management personnel at DDN facilities.  Back issues may
  be obtained via FTP (or Kermit) from NIC.DDN.MIL [192.112.36.5]
  using login="anonymous" and password="guest".  The bulletin pathname is
  scc/ddn-security-yynn (where "yy" is the year the bulletin is issued
  and "nn" is a bulletin number, e.g. scc/ddn-security-9428).
**************************************************************************

+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +
!                                                                       !
!     The following important  advisory was  issued by the Automated    !
!     Systems Security Incident Support Team (ASSIST) and is being      !
!     relayed unedited via the Defense Information Systems Agency's     !
!     Security Coordination Center  distribution  system  as a  means   !
!     of providing  DDN subscribers with useful security information.   !
!                                                                       !
+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +

<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

          Automated Systems Security Incident Support Team
                                                _____
             ___   ___  _____   ___  _____     |     /
      /\    /   \ /   \   |    /   \   |       |    / Integritas
     /  \   \___  \___    |    \___    |       |   <      et
    /____\      \     \   |        \   |       |    \ Celeritas
   /      \ \___/ \___/ __|__  \___/   |       |_____\
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

                       Bulletin  95-23

       Release date: 6 June, 1995, 11:30 AM EDT (GMT -4)

SUBJECT: wu-ftpd Mis-configuration Vulnerability.

SUMMARY: A problem exists with certain configurations of the
Washington University ftpd which may allow root access from any
account on the system.  This bulletin provides updated information
to ASSIST bulletin 94-12, which can be referenced for additional
background information on this problem.

BACKGROUND: Some pre-compiled wu-ftpd-2.4 binaries distributed with
Linux have a vulnerable configuration.  Other users of wu-ftpd
should take this opportunity to verify the configuration of their
daemons are not vulnerable.  NOTE: Versions of wu-ftpd prior to 2.4
contain serious security vulnerabilities and should be updated
immediately.

In its original form, the vulnerability was not enabled by default.
However, certain distributions of Linux contain a wu.ftpd that has
been compiled with a vulnerable configuration.  This vulnerability
has been confirmed for Linux Slackware-2.1 and 2.2.  Other versions
may also be affected.  Instructions for testing systems for the
vulnerability (including non-Linux) are included in this bulletin.

The pre-compiled binaries shipped with Linux Slackware distributions
are vulnerable.  The variable _PATH_EXECPATH was set to "/bin" in
the configuration file src/pathnames.h when the distribution binary
was built.  _PATH_EXECPATH should be set to "/bin/ftp-exec" or a
similar directory that does not contain a shell or command
interpreter.  The source code shipped with the Linux distributions
contains the correct value ("/bin/ftp-exec") (which should be
verified before recompiling) despite the incorrect distribution
binary.  Floppy-only distributions of Linux do not contain source
code.  The latest version of the wu-ftpd source code can be
obtained from:

ftp://wuarchive.wustl.edu/packages/wuarchive-ftpd/wu-ftpd-2.4.tar.Z

The patch file wu-ftpd-2.4.diff.gz for Linux contains incorrect
information.  This should be corrected and verified before
recompiling.  The diff(1) file exists to modify the wu-ftpd source
code to allow it to compile on Linux.  The application of this
diff(1) file patch will configure wu-ftpd with the vulnerability in
place.

IMPACT: Anyone who has a local account on the system offering ftp
services with the vulnerable configuration may gain root access.
Support for anonymous ftp access is not required to exploit this
vulnerability.

RECOMMENDED SOLUTIONS: wu-ftpd configurations should be checked for
existence of the vulnerability, and corrective action taken to
immediately remove the problem if found.

Detection
Vulnerable wu-ftpd configurations can be detected by executing (as
a user) the commands below or by running strings(1) against the
wu-ftpd daemon.

A. Detection with user commands.
   To test your configuration to see if you are vulnerable, you can
   execute the following commands:
   srchost> ftp ftphost
   Connected to ftphost
   220 ftphost FTP server (Version wu-2.4(2) Mon Apr 18 09:12:35
      GMT+1000 1994) ready.
   Name (srchost:user):
   331 Password required for user.
   Password:
   230 User user logged in.
   ftp> quote site exec echo problem
   200-echo problem
   200-problem
   200  (end of 'echo problem')
   ftp> quit
   221 Goodbye.
   srchost>

   If you receive the line "200-problem", then your site is
   vulnerable.  Note that this does not work for anonymous ftp
   access, or for all vulnerable configurations.

B. Detection using strings(1)
   Determine the location of the SITE EXEC path by executing the
   following command on the src/pathnames.h file:
   $ grep _PATH_EXECPATH pathnames.h
   #define _PATH_EXECPATH  "/bin/ftp-exec"
   $

   Use the output of this command to verify that the currently
   running binary is configured the same as the source code.  Note,
   you should consult your documentation for strings(1) to determine
   the correct switch for examining the entire binary:
   $ strings -a wu.ftpd | grep "/bin/ftp-exec"
   /bin/ftp-exec
   $
   If the binary contains the same pathname for _PATH_EXECPATH, then
   you have determined the correct location for the SITE EXEC
   commands.  The directory defined by _PATH_EXECPATH should not
   contain a shell or command interpreter (such as perl) and should
   not be world or group writeable, nor should any directory back to
   the root directory (/) be group or world writeable.  Permissions
   511 are acceptable.

Recovery
   If you have the vulnerability and you are unsure how to eliminate
   it you should mmediately disable your ftp daemon until the
   configuration can be corrected.

A. Temporary workaround
   If you are unsure how to rebuild a new ftpd daemon, then an
   interim workaround is to disable the existing service.  Note: This
   will cause all incoming ftp requests to fail.
   1.  become root
   2.  comment out ftp in /etc/inetd.conf by inserting a "#" at the
   beginning of the ftp line,  ie:
   #ftp     stream  tcp     <rest of normal ftp line here>
   3.  Restart the inetd process.  On most systems, this is done by
   sending a HUP signal to the inetd process.  For example:
   On System V systems
   # /bin/ps -ef | grep inetd | grep -v grep
                        or
   On BSD systems
   # /bin/ps -aux | grep inetd | grep -v grep
   followed by:
   # kill -HUP  <pid gained by above line>
   You should verify that the ftp service has been disabled by
   attempting to connect to it.  You should see a "connection
   refused" message.

B. Correcting the vulnerable configuration.
   Ensure that the _PATH_EXECPATH definition in src/pathnames.h is
   "/bin/ftp-exec" and not "/bin" or any other system directory
   containing a shell or interpreter, and then recompile.  If the
   wu-ftpd-2.4.diff.gz patch has been applied on Linux systems, the
   patched version of pathnames.h will be vulnerable.  This file
   should be edited manually before the rebuild to correct the
   _PATH_EXECPATH definition to "/bin/ftp-exec".  Replace the
   existing ftpd binary with the newly built version.

C. Instructions to enable SITE EXEC
   Once the running binary has been confirmed as not containing the
   vulnerable configuration, the SITE EXEC commands can be enabled
   through the following procedure.
   1.  Ensure that the _PATH_EXECPATH definition in pathnames.h is
   "/bin/ftp-exec" and not "/bin" or any other system directory
   containing a shell.  This should also be checked in the binary
   version (see "Detection B" section above).
   2.  Create ~ftp/bin/ftp-exec.  This should be owned by root,
   permissions set to 555.
   3.  Copy the statically linked binaries that you want available
   for execution by SITE EXEC into the ~ftp/bin/ftp-exec directory.
   These should be owned by root with  permissions set as 111.  The
   binaries should never be a shell or command interpreter that
   allows arbitrary programs to be run.
   4.  If you want the DIR ftp command, you will need a hard link
   from ~ftp/bin/ls to ~ftp/bin/ftp-exec/ls or a copy of ls in
   ~ftp/bin.

   The instructions above enable SITE EXEC commands for anonymous
   users only.  To enable SITE EXEC commands for normal ftp users:
   5.  Create a symbolic link from /bin/ftp-exec to
   ~ftp/bin/ftp-exec.

   You should follow file ownership, group membership and
   permissions strictly according to your documentation.  Note that
   some versions of ftp contain incorrect information for setting
   file permissions and ownership.  Further information can be
   found in:

   ftp://assist.mil/pub/general.info/securing.info.servers

ASSIST would like to thank the AUSCERT for information contained in
this bulletin.

<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

ASSIST is an element of the Defense Information Systems Agency
(DISA), Center for Information Systems Security (CISS), that
provides service to the entire DoD community. Constituents
of the DoD with questions about ASSIST or computer security
security issues, can contact ASSIST using one of the methods
listed below.  Non-DoD organizations/institutions, contact
the Forum of Incident Response and Security Teams (FIRST)
(FIRST) representative.  To obtain a list of FIRST member
organizations and their constituencies send an email to
[e-mail] with an empty "subject" line and a message body
containing the line "send first-contacts".

ASSIST Information Resources: To be included in the distribution
list for the ASSIST bulletins, send your Milnet (Internet) e-mail
address to [e-mail].  Back issues of ASSIST
bulletins, and other security related information, are available
from the ASSIST BBS at 703-607-4710, DSN 327-4710, and through
anonymous FTP from assist.mil (IP address 199.211.123.11).  Note:
assist.mil will only accept anonymous FTP connections from Milnet
addresses that are registered with the NIC or DNS.  If your system
is not registered, you must provide your MILNET IP address to ASSIST
before access can be provided.

ASSIST Contact Information:
PHONE: [phone] (or 703-756-7974 DSN 289), duty hours are 06:00
to 22:30 EDT (GMT -4) Monday through Friday.  During off duty hours,
weekends and holidays, ASSIST can be reached via pager at 800-791-
4857.  The page will be answered within 30 minutes, however if a
quicker response is required, prefix the phone number with "999".
ELECTRONIC MAIL: Send to [e-mail].
ASSIST BBS: Leave a message for the "sysop".

Reference herein to any specific commercial product, process, or
service by trade name, trademark manufacturer, or otherwise, does
not constitute or imply its endorsement, recommendation, or
favoring by ASSIST.  The views and opinions of authors expressed
herein shall not be used for advertising or product endorsement
purposes.

****************************************************************************
*                                                                          *
*    The point of contact for MILNET security-related incidents is the     *
*    Security Coordination Center (SCC).                                   *
*                                                                          *
*               E-mail address: [e-mail]                            *
*                                                                          *
*               Telephone: [phone]                                *
*                                                                          *
*    NIC Help Desk personnel are available from 7:00 a.m.-7:00 p.m. EST,   *
*    Monday through Friday except on federal holidays.                     *
*                                                                          *
****************************************************************************

PLEASE NOTE: Some users outside of the DOD computing communities may receive
DDN Security bulletins.  If you are not part of  the DOD community, please
contact your agency's incident response team to report incidents.  Your
agency's team will coordinate with DOD.  The Forum of Incident Response and
Security Teams (FIRST) is a world-wide organization.  A list of FIRST member
organizations and their constituencies can be obtained by sending email to
[e-mail] with an empty subject line and a message body containing
the line: send first-contacts.

This document was prepared as an service to the DOD community.  Neither the
United States Government nor any of their employees, makes any warranty,
expressed or implied, or assumes any legal liability or responsibility for
the accuracy, completeness, or usefulness of any information, product, or
process disclosed, or represents that its use would not infringe privately
owned rights.  Reference herein to any specific commercial products, process,
or service by trade name, trademark manufacturer, or otherwise, does not
necessarily constitute or imply its endorsement, recommendation, or favoring
by the United States Government.  The opinions of the authors expressed herein
do not necessarily state or reflect those of the United States Government,
and shall not be used for advertising or product endorsement purposes.