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CERT Advisory CA-2000-13 Two Input Validation Problems In FTPD

Original release date: July 7, 2000
Last revised: --
Source: CERT/CC

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

Systems Affected

* Any system running wu-ftpd 2.6.0 or earlier
* Any system running ftpd derived from wu-ftpd 2.0 or later
* Some systems running ftpd derived from BSD ftpd 5.51 or BSD ftpd
5.60 (the final BSD release)

Overview

A vulnerability involving an input validation error in the "site exec"
command has recently been identified in the Washington University ftpd
(wu-ftpd) software package. Sites running affected systems are advised
to update their wu-ftpd software as soon as possible.

A similar but distinct vulnerability has also been identified that
involves a missing format string in several setproctitle() calls. It
affects a broader number of ftp daemons. Please see Appendix A of this
document for specific information about the status of specific ftpd
implementations and solutions.

I. Description

"Site exec" Vulnerability

A vulnerability has been identified in wu-ftpd and other ftp daemons
based on the wu-ftpd source code. Wu-ftpd is a common package used to
provide file transfer protocol (ftp) services. This vulnerability is
being discussed as the wu-ftpd "site exec" or "lreply" vulnerability
in various public forums. Incidents involving the exploitation of this
vulnerability-which enables remote users to gain root privileges-have
been reported to the CERT Coordination Center.

The problem is described in AUSCERT Advisory AA-2000.02, "wu-ftpd
'site exec' Vulnerability," which is available from

ftp://ftp.auscert.org.au/pub/auscert/advisory/AA-2000.02

The wu-ftpd "site exec" vulnerability is the result of missing
character-formatting argument in several function calls that implement
the "site exec" command functionality. Normally if "site exec" is
enabled, a user logged into an ftp server (including the 'ftp' or
'anonymous' user) may execute a restricted subset of quoted commands
on the server itself. However, if a malicious user can pass character
format strings consisting of carefully constructed *printf()
conversion characters (%f, %p, %n, etc) while executing a "site exec"
command, the ftp daemon may be tricked into executing arbitrary code
as root.

The "site exec" vulnerability appears to have been in the wu-ftpd code
since the original wu-ftpd 2.0 came out in 1993. Any vendors who have
based their own ftpd distributions on this vulnerable code are also
likely to be vulnerable.

The vulnerability appears to be exploitable if a local user account
can be used for ftp login. Also, if the "site exec" command
functionality is enabled, then anonymous ftp login allows sufficient
access for an attack.

setproctitle() Vulnerability

A separate vulnerability involving a missing character-formatting
argument in setproctitle(), a call which sets the string used to
display process identifier information, is also present in wu-ftpd.
Other ftpd implementations have been found to have vulnerable
setproctitle() calls as well, including those from proftpd and
OpenBSD.

The setproctitle() vulnerability appears to have been present in
various ftpd implementations since at least BSD ftpd 5.51 (which
predates wuarchive-ftpd 1.0). It has also been confirmed to be present
in BSD ftpd 5.60 (the final BSD release). Any vendors who have based
their own ftpd distributions on this vulnerable code are also likely
to be vulnerable.

It should be noted that many operating systems do not support
setproctitle() calls. However, other software engineering defects
involving the same type of missing character-formatting argument may
be present.

Intruder Activity

One possible indication you are being attacked with either of these
vulnerabilities may be the appearance of syslog entries similar to the
following:

Jul 4 17:43:25 victim ftpd[3408]: USER ftp
Jul 4 17:43:25 victim ftpd[3408]: PASS [malicious shellcode]
Jul 4 17:43:26 victim ftpd[3408]: ANONYMOUS FTP LOGIN FROM
attacker.example.com [10.29.23.19], [malicious shellcode]
Jul 4 17:43:28 victim-site ftpd[3408]: SITE EXEC (lines: 0):
%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%
.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.
f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f
%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%
.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.
f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f
%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%.f%c%c%c%.f|%p
Jul 4 17:43:28 victim ftpd[3408]: FTP session closed

Details and exploits for both the "site exec" and setproctitle()
vulnerabilities have been posted in various public forums. Please see

http://www.securityfocus.com/vdb/bottom.html?section=discussion&vid=1387
http://www.securityfocus.com/vdb/bottom.html?section=discussion&vid=1438
http://ciac.llnl.gov/ciac/bulletins/k-054.shtml

The CERT/CC has received reports of both of these vulnerabilities
being successfully exploited on the Internet. Please check our Current
Activity page for updates regarding intruder activity involving these
vulnerabilities.

II. Impact

By exploiting any of these input validation problems, local or remote
users logged into the ftp daemon may be able execute arbitrary code as
root. An anonymous ftp user may also be able to execute arbitrary code
as root.

III. Solution

Upgrade your version of ftpd

Please see Appendix A of this advisory for more information about the
availability of updated ftpd packages specific for your system.

Apply a patch from your vendor

If you are running vulnerable ftpd implementations and cannot upgrade,
you need to apply the appropriate vendor patches and recompile and/or
reinstall the ftpd server software.

Appendix A contains information provided by vendors for this advisory.
We will update the appendix as we receive more information. If you do
not see your vendor's name, the CERT/CC did not hear from that vendor.
Please contact your vendor directly.

Disable ftp services

If neither an upgrade nor a patch can be applied, the CERT/CC
recommends disabling all vulnerable wu-ftpd and proftpd servers. While
disabling "site exec" command functionality or anonymous ftp access
minimizes exposure to the "site exec" vulnerability, neither is a
complete solution and may not mitigate against the risks involved with
exposure to the setproctitle() vulnerability.

Appendix A. Vendor Information

BSDI

Current versions of BSD/OS do not include any version of wu-ftpd. The
BSDI ftpd is not vulnerable to the reported problems; it is not based
on the wu-ftpd code.

The version of ftpd in modern versions of BSD/OS is not vulnerable to
the generic setproctitle() vulnerabilities.

Caldera Systems, Inc

Please see CSSA-2000-020.0 regarding the wu-ftpd issue and OpenLinux:

ftp://ftp.calderasystems.com/pub/OpenLinux/security/CSSA-2000-020.0.txt

Conectiva S.A.

Please see:

http://www.securityfocus.com/templates/archive.pike?list=1&msg=This email address is being protected from spambots. You need JavaScript enabled to view it.

Debian GNU/Linux

Please see the following regarding the wu-ftpd "site exec" issue:

http://www.debian.org/security/2000/20000623

FreeBSD, Inc.

Please see FreeBSD-SA-00:29, Security Advisory for wu-ftpd in the
ports collection, for complete information. In part it states:

The wu-ftpd port is not installed by default, nor is it "part of
FreeBSD" as such: it is part of the FreeBSD ports collection,
which contains over 3400 third-party applications in a
ready-to-install format. The ports collections shipped with
FreeBSD 3.5 and 4.0 contains this problem since it was
discovered after the release. FreeBSD makes no claim about the
security of these third-party applications, although an effort
is underway to provide a security audit of the most
security-critical ports.

[With respect to setproctitle()] it turns out that FreeBSD fixed this
bug in the system ftpd back in 1996, so it is not present in all
versions of FreeBSD since 2.2.0.

We also ship optional third-party ftpds in the ports collection: we
had patched wu-ftpd and believed it to be fixed (it was the subject of
advisory SA-00:29), but in light of the other recent email from CERT.
We will re-check to make sure all of the vulnerabilities were patched.
Proftpd is also currently vulnerable but [has been patched]. Other
third-party ftpds may or may not be vulnerable at this time (we advise
users to install ports at their own risk), and we will release
security advisories as they are discovered and fixed.

Hewlett-Packard Company

HP is vulnerable, patches in process, watch for the HP security
bulletin to be issued.

MandrakeSoft Inc.

Please see the MANDRAKE 7.1 update section for wu-ftpd information at:

http://www.linux-mandrake.com/en/fupdates.php3

Microsoft Coporation

The IIS FTP service is not is not affected by these issues.

MIT Kerberos Development Team

It seems that the MIT Kerberos ftpd is based on BSD ftpd revision
5.40, and has never contained any serious format string related bugs
for some reason. It is possible that by defining an undocumented CPP
macro SETPROCTITLE, calls to setproctitle() can be made, however,
there is an internally declared setproctitle() function that does not
take a format string as its argument, and is hence not vulnerable.

ProFTPD Project

Upgrade to ProFTPD 1.2.0

Please see the discussion concerning setproctitle() at

http://www.proftpd.org/proftpd-l-archive/00-07/msg00059.html
http://www.proftpd.org/proftpd-l-archive/00-07/msg00060.html
http://bugs.proftpd.net/show_bug.cgi?id=121
http://www.proftpd.net/security.html

OpenBSD

The setproctitle bug is in OpenBSD. Please see:

http://www.openbsd.org/errata.html#ftpd

Redhat

Please see RHSA-2000-039-02 regarding the wu-ftpd issue:

http://www.redhat.com/support/errata/RHSA-2000-039-02.html

Slackware Linux Project

Please see the patches made available regarding the wu-ftpd issue, at:

ftp://ftp.slackware.com/pub/slackware/slackware-7.1/patches/wu-ftpd-patch.README

Sun Microsystems

[...] Our engineering team and they do not feel that Solaris is
vulnerable.

SuSE Ltd.

Please see SuSE Security Announcement #53 regarding the wu-ftpd issue,
at:

http://www.suse.de/de/support/security/suse_security_announce_53.txt

WU-FTPD Development Group

The WU-FTPD Development Group's primary distribution site is mirrored
world-wide. A list of mirrors is available from:

http://www.wu-ftpd.org/mirrors.txt

If possible, please use a mirror to obtain patches or the latest
version.

Upgrade your version of wu-ftpd

The latest release of wu-ftpd, version 2.6.1, has been released to
address these and several other security issues:

ftp://ftp.wu-ftpd.org/pub/wu-ftpd/wu-ftpd-2.6.1.tar.gz
ftp://ftp.wu-ftpd.org/pub/wu-ftpd/wu-ftpd-2.6.1.tar.gz.asc
ftp://ftp.wu-ftpd.org/pub/wu-ftpd/wu-ftpd-2.6.1.tar.Z
ftp://ftp.wu-ftpd.org/pub/wu-ftpd/wu-ftpd-2.6.1.tar.Z.asc

Apply a patch

The wu-ftpd developers have published the following patch for wu-ftpd
2.6.0:

ftp://ftp.wu-ftpd.org/pub/wu-ftpd/patches/apply_to_2.6.0/lreply-buffer-overflow.patch
_________________________________________________________________

The CERT Coordination Center thanks Gregory Lundberg and Theo de Raadt
for their help in developing this advisory.
_________________________________________________________________

Author: Jeffrey S. Havrilla
______________________________________________________________________

This document is available from:
http://www.cert.org/advisories/CA-2000-13.html
______________________________________________________________________

CERT/CC Contact Information

Email: This email address is being protected from spambots. You need JavaScript enabled to view it.
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
Postal address:
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
U.S.A.

CERT personnel answer the hotline 08:00-20:00 EST(GMT-5) / EDT(GMT-4)
Monday through Friday; they are on call for emergencies during other
hours, on U.S. holidays, and on weekends.

Using encryption

We strongly urge you to encrypt sensitive information sent by email.
Our public PGP key is available from

http://www.cert.org/CERT_PGP.key

If you prefer to use DES, please call the CERT hotline for more
information.

Getting security information

CERT publications and other security information are available from
our web site

http://www.cert.org/

To be added to our mailing list for advisories and bulletins, send
email to This email address is being protected from spambots. You need JavaScript enabled to view it. and include SUBSCRIBE
your-email-address in the subject of your message.

* "CERT" and "CERT Coordination Center" are registered in the U.S.
Patent and Trademark Office.
______________________________________________________________________

NO WARRANTY
Any material furnished by Carnegie Mellon University and the Software
Engineering Institute is furnished on an "as is" basis. Carnegie
Mellon University makes no warranties of any kind, either expressed or
implied as to any matter including, but not limited to, warranty of
fitness for a particular purpose or merchantability, exclusivity or
results obtained from use of the material. Carnegie Mellon University
does not make any warranty of any kind with respect to freedom from
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_________________________________________________________________

Conditions for use, disclaimers, and sponsorship information

Revision History
July 7, 2000: Initial release

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