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                 NetBSD Security Advisory 2000-018
                 =================================

Topic:          One-byte buffer overrun in ftpd
Version:        All official releases up to and including 1.5
Severity:       possible remote root compromise.
Fixed:          NetBSD-current: December 4, 2000
                NetBSD 1.4 branch: December 14, 2000
                NetBSD 1.5 branch: December 13, 2000

Abstract
========

A one-byte buffer overrun was found in the ftp server daemon
(/usr/libexec/ftpd).  It is rumored to be remotely exploitable.

Systems running ftpd are vulnerable.

ftpd is usually started from inetd; inetd is configured through the
/etc/inetd.conf file.

As of the release date of this advisory, all of past NetBSD releases,
including NetBSD 1.5, are vulnerable.  

Fresh installs of NetBSD 1.5 are not vulnerable as ftpd is disabled by
default in /etc/inetd.conf; however, a system upgraded from an earlier
release to 1.5 may still be using an old inetd.conf with ftpd still
enabled, or it may need to run and ftp server and will thus have it
enabled.

Technical Details
=================

The replydirname() function is used in ftpd to return pathname strings
to the ftp client.  It contained an erroneous bounds check.

Solutions and Workarounds
=========================

All NetBSD official releases up to 1.5, have a vulnerable ftp server
binary in /usr/libexec/ftpd.  We need to replace it to fix the
problem.

If you do not run ftpd on your system, you system is not vulnerable.  Check
/etc/inetd.conf to see if you have a line starts with "ftp".  We suggest
you to apply the fix anyways, in case you want to run ftpd in the future.
Note that NetBSD 1.5 does not run ftpd by default (inetd.conf has a
commented-out "ftp" line).

Systems running NetBSD-current dated from before December 4, 2000 should be
upgraded to NetBSD-current dated December 4, 2000 or later.

Systems running releases older than NetBSD 1.4 should be upgraded to
NetBSD 1.4.3 before applying the fixes described here.

Systems running NetBSD 1.4.3 should apply the patch contained in

    ftp://ftp.NetBSD.ORG/pub/NetBSD/misc/security/patches/20001220-ftpd-1.4.3

Systems running NetBSD 1.5 should apply the patch contained in 

    ftp://ftp.NetBSD.ORG/pub/NetBSD/misc/security/patches/20001220-ftpd-1.5

Different patches are needed because the vulnerable function was
moved from ftpd.c to cmds.c.

In the following examples, we assume that you have full source code
under /usr/src, and have stored a copy of the patch in a file named
"20001220-ftpd" in /usr/src/libexec/ftpd

In either case, the patch should be applied in /usr/src/libexec/ftpd
and ftpd should then be rebuilt and reinstalled using the following
commands:

        # cd /usr/src/libexec/ftpd
        # patch < 20001220-ftpd
        # make cleandir
        # make depend 
        # make
        # make install

To be sure that the system is no longer vulnerable, you should ensure
that all ftpd processes running on the system started after ftpd was
reinstalled.

Thanks To
=========

Kristian Vlaardingerbroek <kris@obit.nl>


Revision History
================

        2000/12/20 - Initial revision


More Information
================

Information about NetBSD and NetBSD security can be found at
http://www.NetBSD.ORG/ and http://www.NetBSD.ORG/Security/.


Copyright 2000, The NetBSD Foundation, Inc.  All Rights Reserved.

$NetBSD: NetBSD-SA2000-018.txt,v 1.1 2000/12/20 18:46:53 sommerfeld Exp $

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