CERT Advisory CA-2000-13 Two Input Validation Problems In FTPD
Jul 09, 2000, 15:06 (
Date: Fri, 7 Jul 2000 15:49:21 -0700
From: Aleph One
Subject: CERT Advisory CA-2000-1
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CERT Advisory CA-2000-13 Two Input Validation Problems In FTPD
Original release date: July 7, 2000
Last revised: --
A complete revision history is at the end of this file.
* 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)
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.
"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
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
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.
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
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
One possible indication you are being attacked with either of these
vulnerabilities may be the appearance of syslog entries similar to the
Jul 4 17:43:25 victim ftpd: USER ftp
Jul 4 17:43:25 victim ftpd: PASS [malicious shellcode]
Jul 4 17:43:26 victim ftpd: ANONYMOUS FTP LOGIN FROM
attacker.example.com [10.29.23.19], [malicious shellcode]
Jul 4 17:43:28 victim-site ftpd: SITE EXEC (lines: 0):
Jul 4 17:43:28 victim ftpd: FTP session closed
Details and exploits for both the "site exec" and setproctitle()
vulnerabilities have been posted in various public forums. Please see
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
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
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
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:
Copyright © 2000 Caldera Systems, Inc.
Please see the following regarding the wu-ftpd "site exec" issue:
Copyright © 1997-2000 SPI
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
[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.
HP is vulnerable, patches in process, watch for the HP security
bulletin to be issued.
Please see the MANDRAKE 7.1 update section for wu-ftpd information at:
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.
Upgrade to ProFTPD 1.2.0
Please see the discussion concerning setproctitle() at
The setproctitle bug is in OpenBSD. Please see:
Please see RHSA-2000-039-02 regarding the wu-ftpd issue:
Copyright © 2000 Red Hat, Inc. All rights reserved.
Slackware Linux Project
Please see the patches made available regarding the wu-ftpd issue, at:
[...] Our engineering team and they do not feel that Solaris is
Please see SuSE Security Announcement #53 regarding the wu-ftpd issue,
WU-FTPD Development Group
The WU-FTPD Development Group's primary distribution site is mirrored
world-wide. A list of mirrors is available from:
If possible, please use a mirror to obtain patches or the latest
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:
Apply a patch
The wu-ftpd developers have published the following patch for wu-ftpd
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:
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July 7, 2000: Initial release
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