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Home : Advisories : One-byte buffer overrun in ftpd

Title: One-byte buffer overrun in ftpd
Released by: NetBSD
Date: 21st December 2000
Printable version: Click here

                 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



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


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


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


Systems running NetBSD 1.5 should apply the patch contained in


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


# 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


Thanks To


Kristian Vlaardingerbroek 

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 $


Version: 2.6.3ia

Charset: noconv







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