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AUSCERT External Security Bulletin Redistribution
ESB-2001.164 -- FreeBSD-SA-01:33.ftpd-glob [REVISED]
globbing vulnerability in ftpd
24 April 2001
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Product: ftpd
Vendor: FreeBSD
Operating System: FreeBSD 3.x (all releases)
FreeBSD 4.x (all releases)
FreeBSD 3.5-STABLE
FreeBSD 4.3-RC (prior to the correction date)
BSD
Linux
Unix
Impact: Execute Arbitrary Code/Commands
Root Compromise
Access Required: Remote
Ref: ESB-2001.155
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FreeBSD-SA-01:33 Security Advisory
FreeBSD, Inc.
Topic: globbing vulnerability in ftpd [REVISED]
Category: core
Module: ftpd/libc
Announced: 2001-04-17
Revised: 2001-04-19
Credits: John McDonald and Anthony Osborne, COVERT Labs
Affects: FreeBSD 3.x (all releases), FreeBSD 4.x (all releases),
FreeBSD 3.5-STABLE and 4.3-RC prior to the
correction date.
Corrected: 2001-04-17 (FreeBSD 4.3-RC)
2001-04-17 (FreeBSD 3.5-STABLE)
Vendor status: Corrected
FreeBSD only: NO
0. Revision History
2001-04-17 v1.0 Initial release
2001-04-19 v1.1 Corrected patch and patch instructions
I. Background
Numerous FTP daemons, including the daemon distributed with FreeBSD,
use server-side globbing to expand pathnames via user input. This
globbing is performed by FreeBSD's glob() implementation in libc.
II. Problem Description
The glob() function contains potential buffer overflows that may be
exploitable through the FTP daemon. If a directory with a name of
a certain length is present, a remote user specifying a pathname
using globbing characters may cause arbitrary code to be executed
on the FTP server as user running ftpd, usually root.
Additionally, when given a path containing numerous globbing
characters, the glob() functions may consume significant system
resources when expanding the path. This can be controlled by
setting user limits via /etc/login.conf and setting limits on
globbing expansion.
All versions of FreeBSD prior to the correction date, including
FreeBSD 3.5.1 and 4.2 contain this problem. The base system that
will ship with FreeBSD 4.3 does not contain this problem since it
was corrected before the release.
III. Impact
Remote users may be able to execute arbitrary code on the FTP server
as the user running ftpd, usually root.
The FTP daemon supplied with FreeBSD is enabled by default to allow
access to authorized local users and not anonymous users, thus
limiting the impact to authorized local users.
IV. Workaround
If the FTP daemon is executed from inetd, disable the FTP daemon by
commenting out the ftp line in /etc/inetd.conf, then reload the
inetd configuration by executing the following command as root:
# killall -HUP inetd
V. Solution
One of the following:
1) Upgrade to FreeBSD 4.3-RC or 3.5.1-STABLE after the correction
date.
2) Download the patch and detached PGP signature from the following
location:
The following patch applies to FreeBSD 4.x:
# fetch ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-01:33/glob.4.x.patch
# fetch ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-01:33/glob.4.x.patch.asc
The following patch applies to FreeBSD 3.x:
# fetch ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-01:33/glob.3.x.patch
# fetch ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-01:33/glob.3.x.patch.asc
Verify the detached signature using your PGP utility.
Issue the following commands as root:
# cd /usr/src
# patch -p < /path/to/patch
# cp /usr/src/include/glob.h /usr/include/
# cd /usr/src/lib/libc
# make all install
# cd /usr/src/libexec/ftpd
# make all install
If the FTP daemon is running standalone, it will have to be manually
stopped and restarted.
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