ftpd Vulnerabilities

Original issue date: April 14, 1994
Last revised: September 23, 1997
Updated Copyright Statement

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

The CERT Coordination Center has received information concerning two vulnerabilities in some ftpd implementations. The first is a vulnerability with the SITE EXEC command feature of the FTP daemon (ftpd) found in versions of ftpd that support the SITE EXEC feature. This vulnerability allows local or remote users to gain root access. The second vulnerability involves a race condition found in the ftpd implementations listed in Section I. below. This vulnerability allows local users to gain root access.

Sites using these implementations are vulnerable even if they do not support anonymous FTP.

As these vulnerabilities are widely known, we strongly recommend that any site running a version of ftpd listed below take steps to immediately upgrade or disable their FTP daemon. Also potentially at risk are sites whose ftpd is derived from the DECWRL or wuarchive ftpd code containing the SITE EXEC feature.

For additional information or assistance, contact the developer or vendor of your ftpd implementation.

We will update this advisory as we receive additional information. Please check advisory files regularly for updates that relate to your site.


I. Description

There is a vulnerability in the SITE EXEC command feature of ftpd that allows any remote or local user to obtain root access. There is also a vulnerability due to a race condition in these implementations.

Versions known to be vulnerable to these problems are:
wuarchive ftpd versions 2.0-2.3 (version 2.2 patched the SITE EXEC problem, but not the race condition) DECWRL ftpd versions prior 5.93
BSDI ftpd version 1.1 prior to patch 5

The SITE EXEC vulnerability affects your ftpd only if the SITE EXEC command feature has been explicitly activated at your site. This functionality is not activated by default. Sites that have not enabled the SITE EXEC feature are not at risk from this vulnerability. However, since the race condition does not have an easily applied workaround, CERT recommends that you upgrade to one of the versions listed below.

II. Impact

Anyone (remote or local) can gain root access on a host running a vulnerable FTP daemon. Support for anonymous FTP is not required to exploit this vulnerability.

III. Solution

Affected sites can solve both of these problems by upgrading to the latest version of ftpd. These versions are listed below. Be certain to verify the checksum information to confirm that you have retrieved a valid copy.

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

For wuarchive ftpd, you can obtain version 2.4 via anonymous FTP from wuarchive.wustl.edu, in the "/packages/wuarchive-ftpd" directory. If you are currently running version 2.3, a patch file is available.

                        BSD        SVR4
     File               Checksum   Checksum    MD5 Digital Signature
     -----------------  --------   ---------   --------------------------------
     wu-ftpd-2.4.tar.Z  38213  181  20337 362  cdcb237b71082fa23706429134d8c32e
     patch_2.3-2.4.Z    09291    8  51092  16  5558a04d9da7cdb1113b158aff89be8f
     For DECWRL ftpd, sites can obtain version 5.93 via anonymous FTP
     from gatekeeper.dec.com in the "/pub/misc/vixie" directory.
                        BSD        SVR4
     File               Checksum   Checksum    MD5 Digital Signature
     -----------------  --------   --------- --------------------------------
     ftpd.tar.gz        38443  60  1710 119  ae624eb607b4ee90e318b857e6573500
     For BSDI systems, patch 005 should be applied to version 1.1 of
     the BSD/386 software.  You can obtain the patch file via
     anonymous FTP from ftp.bsdi.com in the "/bsdi/patches-1.1"
     directory.
                        BSD        SVR4
     File               Checksum   Checksum    MD5 Digital Signature
     -----------------  --------   ---------   --------------------------------
     BU110-005          35337 272  54935 543   1f454d4d9d3e1397d1eff0432bd383cf

The CERT Coordination Center wishes to thank Neil Woods and Karl Strickland for finding and reporting the wustl FTP daemon bug. We also wish to thank Bryan O'Connor and Chris Myers of Washington University in St. Louis, Paul Vixie of Vixie Enterprises, and Tony Sanders of BSDI for their invaluable assistance in resolving this problem.


Copyright 1994 Carnegie Mellon University.


Revision History
Sep. 23, 1997   Updated copyright statement
Aug. 30, 1996   Removed references to README files because advisories
                themselves are now updated.