Vulnerability Report For WU-FTPD Server
Bugtraq ID: 3581
CVE Name: CVE-2001-0550
CERT: VU#886083
Title: WU-FTPD Improper Ftpglob Error Handling Vulnerability
Class: Failure to handle exceptional conditions
Remotely Exploitable: Yes
Locally Exploitable: Yes
Release Mode: FORCED RELEASE
Vulnerability Description:
The Washington University FTP daemon (WU-FTPD) is a highly modified and significantly complex version of FTPD that provides some extra features: custom logging, limited remote command support, and other enhancements to the standard BSD version of FTPD.
A problem was found in all versions of Wu-FTPD included by default in all major Linux distributions. Other platforms that ship wu-ftpd and FTP server programs derived from it are affected.
By exploiting this problem, any user who is able to log into a vulnerable version of the WU-FTPD server may be able to execute arbitrary code remotely with the privileges of the server process (usually root) which can lead to complete system compromise.
The problem is due to a combination of bugs, one located within the function responsible for the globbing feature, which fails to properly signal an error to its caller under certain conditions. The glob function does not properly handle the string "~{" as an illegal parameter. The other bug is at the caller, a command parser function, that incorrectly handles the error status returned by the glob function allowing the corruption of the process memory space.
For those interested in a technical description and proof of concept follow towards the end of this advisory.
Vulnerable Packages:
WU-FTPD
All versions of wu-ftpd including and up to 2.6.1 are vulnerable.
Version 2.7.0 snapshots are also vulnerable.
Note that 2.7.0 is has not been released officially and is currently a
testing version, nonetheless certain Linux vendors ship vulnerable
wu-ftpd version 2.7.0 intheir distributions.
Washington University wu-ftpd 2.6.1
+ Caldera OpenLinux Server 3.1
+ Caldera OpenLinux Workstation 3.1
+ Cobalt Qube 1.0
+ Conectiva Linux 7.0
+ Conectiva Linux 6.0
+ MandrakeSoft Corporate Server 1.0.1
+ MandrakeSoft Linux Mandrake 8.1
+ MandrakeSoft Linux Mandrake 8.0 ppc
+ MandrakeSoft Linux Mandrake 8.0
+ MandrakeSoft Linux Mandrake 7.2
+ MandrakeSoft Linux Mandrake 7.1
+ MandrakeSoft Linux Mandrake 7.0
+ MandrakeSoft Linux Mandrake 6.1
+ MandrakeSoft Linux Mandrake 6.0
+ RedHat Linux 7.2 noarch
+ RedHat Linux 7.2 ia64
+ RedHat Linux 7.2 i686
+ RedHat Linux 7.2 i586
+ RedHat Linux 7.2 i386
+ RedHat Linux 7.2 athlon
+ RedHat Linux 7.2 alpha
+ RedHat Linux 7.1 noarch
+ RedHat Linux 7.1 ia64
+ RedHat Linux 7.1 i686
+ RedHat Linux 7.1 i586
+ RedHat Linux 7.1 i386
+ RedHat Linux 7.1 alpha
+ RedHat Linux 7.0 sparc
+ RedHat Linux 7.0 i386
+ RedHat Linux 7.0 alpha
+ TurboLinux TL Workstation 6.1
+ TurboLinux Turbo Linux 6.0.5
+ TurboLinux Turbo Linux 6.0.4
+ TurboLinux Turbo Linux 6.0.3
+ TurboLinux Turbo Linux 6.0.2
+ TurboLinux Turbo Linux 6.0.1
+ TurboLinux Turbo Linux 6.0
+ Wirex Immunix OS 7.0-Beta
+ Wirex Immunix OS 7.0
Washington University wu-ftpd 2.6.0
+ Cobalt Qube 1.0
+ Conectiva Linux 5.1
+ Conectiva Linux 5.0
+ Conectiva Linux 4.2
+ Conectiva Linux 4.1
+ Conectiva Linux 4.0es
+ Conectiva Linux 4.0
+ Debian Linux 2.2 sparc
+ Debian Linux 2.2 powerpc
+ Debian Linux 2.2 arm
+ Debian Linux 2.2 alpha
+ Debian Linux 2.2 68k
+ Debian Linux 2.2
+ RedHat Linux 6.2 sparc
+ RedHat Linux 6.2 i386
+ RedHat Linux 6.2 alpha
+ RedHat Linux 6.1 sparc
+ RedHat Linux 6.1 i386
+ RedHat Linux 6.1 alpha
+ RedHat Linux 6.0 sparc
+ RedHat Linux 6.0 i386
+ RedHat Linux 6.0 alpha
+ RedHat Linux 5.2 sparc
+ RedHat Linux 5.2 i386
+ RedHat Linux 5.2 alpha
+ S.u.S.E. Linux 6.4ppc
+ S.u.S.E. Linux 6.4alpha
+ S.u.S.E. Linux 6.4
+ S.u.S.E. Linux 6.3 ppc
+ S.u.S.E. Linux 6.3 alpha
+ S.u.S.E. Linux 6.3
+ S.u.S.E. Linux 6.2
+ S.u.S.E. Linux 6.1 alpha
+ S.u.S.E. Linux 6.1
+ TurboLinux Turbo Linux 4.0
+ Wirex Immunix OS 6.2
Washington University wu-ftpd 2.5.0
+ Caldera eDesktop 2.4
+ Caldera eServer 2.3.1
+ Caldera eServer 2.3
+ Caldera OpenLinux 2.4
+ Caldera OpenLinux Desktop 2.3
+ RedHat Linux 6.0 sparc
+ RedHat Linux 6.0 i386
+ RedHat Linux 6.0 alpha
Sun Microsystems Inc.
The Sun Cobalt Qube1 is vulnerable.
Solaris is NOT vulnerable to this problem.
As reported by Brent Paulson from Sun regarding Solaris ISP server that ships with a wu-ftpd derived server:
"The Sun engineering group for the SISP in.ftpd product
has verified that we are not vulnerable to the issue
described in the described vulnerability."
Hewlett Packard
As reported by Dan Grove from HP:
" HP-UX is immune to this issue. It was fixed
in conjunction with the last "globbing" issue
announced in CERT Advisory CA-2001-07, released
April 10, 2001. The lab did a complete check/scan
of the globbing software, and fixed this issue then
as well. Customers should apply the patches listed
in HP Security Bulletin #162 released July 19,2001:
HPSBUX0107-162 Security Vulnerability in ftpd and ftp"
Solution/Vendor Information/Workaround:
Wu-FTPD
The WU-FTPD Development Group has released a patch against version 2.6.1.
This patch is available at
ftp://ftp.wu-ftpd.org/pub/wu-ftpd/patches/apply-to-2.6.1/ftpglob.patch.
Additional patches to version 2.6.1 are available in the same directory.
Those running earlier versions are advised to update to version 2.6.1
and apply all supplied patches.
A new version with all these patches applied will be made available
shortly as version 2.6.2. To avoid confusion, we will skip the 2.7.0
version number.
The WU-FTPD Development Group has been made aware that some vendors are shipping vulnerable pre-release, development versions of WU-FTPD software bearing, at least internally, version 2.7.0. All users are advised to verify the version claimed on the initial greeting upon connection to the software (you may need to remove your greeting clause from the WU-FTPD configuration to allow the version information to be displayed). If this greeting claims version 2.7.0 or earlier, they are advised to DOWNGRADE
IMMEDIATELY to version 2.6.1 and apply all supplied patches. To avoid confusion, the WU-FTPD Development Group WILL NOT release version 2.7.0; instead their next version will be numbered 2.8.0. (Users participating the field trials of the develpment version are advised to verify their CVS snapshot, and, if dated on or before July 1, 2001, either upgrade to the current snapshot or downgrade to a patched version 2.6.1.)
RedHat
RedHat Linux had released and advisory and and
SRPMs to address the problem, they can be obtained
from
http://www.redhat.com/support/errata/RHSA-2001-157.html
Conectiva Linux
Fixed packages will be made available in the next days
for all supported Conectiva Linux distributions at
ftp://atualizacoes.conectiva.com.br
Caldera Systems
OpenLinux 2.3
Vulnerable.
Fixed packages were released on 2001/11/28:
ftp://ftp.caldera.com/pub/updates/OpenLinux/2.3/068/
OpenLinux eServer 2.3.1
Vulnerable.
Fixed packages were released on 2001/11/28:
ftp://ftp.caldera.com/pub/updates/eServer/2.3/064/
OpenLinux eDesktop 2.4
Vulnerable.
Fixed packages were released on 2001/11/28:
ftp://ftp.caldera.com/pub/updates/eDesktop/2.4/058/
OpenLinux Workstation 3.1
Not vulnerable. (Does not include wu-ftpd)
OpenLinux Server 3.1
Vulnerable.
Fixed packages were released on 2001/11/28:
ftp://ftp.caldera.com/pub/updates/OpenLinux/3.1/Server/020/
Sun Microsystems
"The only Sun Cobalt Server Appliance that is vulnerable to this exploit is the Qube1. The Qube1 is no longer a supported appliance,
but we do understand the need of having updates available. The following RPM is not officially supported by Sun Cobalt, but offers legacy customers the ability to maintain a limited level of security."
Qube1:
ftp://ftp.cobaltnet.com/pub/unsupported/qube1/rpms/wu-ftpd-2.6.1-C1.NOPAM.mi
ps.rpm
ftp://ftp.cobaltnet.com/pub/unsupported/qube1/srpms/wu-ftpd-2.6.1-C1.NOPAM.s
rc.rpm
SuSE Linux
SuSE have the set of patches to fix the vulnerability. Updated packages that fix the vulnerability are available from the following URLs:
i386 Intel Platform:
SuSE-7.3
ftp://ftp.suse.com/pub/suse/i386/update/7.3/n2/wuftpd-2.6.0-344.i386.rpm
d1b549b8c2d91d66a8b35fe17a1943b3
source rpm:
ftp://ftp.suse.com/pub/suse/i386/update/7.3/zq1/wuftpd-2.6.0-344.src.rpm
9ef0e6ac850499dc0150939c62bc146f
SuSE-7.2
ftp://ftp.suse.com/pub/suse/i386/update/7.2/n2/wuftpd-2.6.0-344.i386.rpm
4583443a993107b26529331fb1e6254d
source rpm:
ftp://ftp.suse.com/pub/suse/i386/update/7.2/zq1/wuftpd-2.6.0-344.src.rpm
aaee0343670feae70ccc9217a8e22211
SuSE-7.1
ftp://ftp.suse.com/pub/suse/i386/update/7.1/n2/wuftpd-2.6.0-346.i386.rpm
347a030a85cb5fcbe32d3d79d382e19e
source rpm:
ftp://ftp.suse.com/pub/suse/i386/update/7.1/zq1/wuftpd-2.6.0-346.src.rpm
aa3e53641f6ce0263196e6f1cb0447c3
SuSE-7.0
ftp://ftp.suse.com/pub/suse/i386/update/7.0/n1/wuftpd-2.6.0-344.i386.rpm
e34eec18ecc10f187f6aa1aa3b24b75b
source rpm:
ftp://ftp.suse.com/pub/suse/i386/update/7.0/zq1/wuftpd-2.6.0-344.src.rpm
fafc8c2bbd68dd5ca3d04228433c359a
SuSE-6.4
ftp://ftp.suse.com/pub/suse/i386/update/6.4/n1/wuftpd-2.6.0-344.i386.rpm
2354abe95b056762c7f6584449291ff2
source rpm:
ftp://ftp.suse.com/pub/suse/i386/update/6.4/zq1/wuftpd-2.6.0-344.src.rpm
507b8d484b13737c9d2b6a68fda0cc26
SuSE-6.3
ftp://ftp.suse.com/pub/suse/i386/update/6.3/n1/wuftpd-2.6.0-347.i386.rpm
9851ad02e656bba8b5e02ed2ddb46845
source rpm:
ftp://ftp.suse.com/pub/suse/i386/update/6.3/zq1/wuftpd-2.6.0-347.src.rpm
5d7c4b6824836ca28b228cc5dcfc4fd6
Sparc Platform:
SuSE-7.3
ftp://ftp.suse.com/pub/suse/sparc/update/7.3/n2/wuftpd-2.6.0-240.sparc.rpm
2d19e4ead17396a1e28fca8745f9629d
source rpm:
ftp://ftp.suse.com/pub/suse/sparc/update/7.3/zq1/wuftpd-2.6.0-240.src.rpm
bdb0b5ddd72f8563db3c8e444a0df7f5
SuSE-7.1
ftp://ftp.suse.com/pub/suse/sparc/update/7.1/n2/wuftpd-2.6.0-242.sparc.rpm
f6b04f284bece6bf3700facccc015ffe
source rpm:
ftp://ftp.suse.com/pub/suse/sparc/update/7.1/zq1/wuftpd-2.6.0-242.src.rpm
1660547ac9a5a3b32a4070d69803cf18
SuSE-7.0
ftp://ftp.suse.com/pub/suse/sparc/update/7.0/n1/wuftpd-2.6.0-241.sparc.rpm
1bd905b095b9a4bb354fc190b6e54a01
source rpm:
ftp://ftp.suse.com/pub/suse/sparc/update/7.0/zq1/wuftpd-2.6.0-241.src.rpm
597263eb7d0fbbf242d519d3c126a441
AXP Alpha Platform:
SuSE-7.1
ftp://ftp.suse.com/pub/suse/axp/update/7.1/n2/wuftpd-2.6.0-252.alpha.rpm
e608bfd2cc9e511c6eb6932c33c68789
source rpm:
ftp://ftp.suse.com/pub/suse/axp/update/7.1/zq1/wuftpd-2.6.0-252.src.rpm
34915af1ca79b27bad8bc2fd3a5cab05
SuSE-7.0
ftp://ftp.suse.com/pub/suse/axp/update/7.0/n1/wuftpd-2.6.0-251.alpha.rpm
86a7d8f60d76a053873bcc13860b0bbb
source rpm:
ftp://ftp.suse.com/pub/suse/axp/update/7.0/zq1/wuftpd-2.6.0-251.src.rpm
9674f9f1630b3107ac22d275705da76e
SuSE-6.4
ftp://ftp.suse.com/pub/suse/axp/update/6.4/n1/wuftpd-2.6.0-251.alpha.rpm
2501444a1e4241e8f6f4cdcc6fd133b0
source rpm:
ftp://ftp.suse.com/pub/suse/axp/update/6.4/zq1/wuftpd-2.6.0-251.src.rpm
34812d943900bdb902ad7edd40e1943f
SuSE-6.3
ftp://ftp.suse.com/pub/suse/axp/update/6.3/n1/wuftpd-2.6.0-250.alpha.rpm
429a49ef9d4d0865fbb443c212b8a8c7
source rpm:
ftp://ftp.suse.com/pub/suse/axp/update/6.3/zq1/wuftpd-2.6.0-250.src.rpm
76467dae0f460677ba80ec907eefca28
PPC Power PC Platform:
SuSE-7.3
ftp://ftp.suse.com/pub/suse/ppc/update/7.3/n2/wuftpd-2.6.0-277.ppc.rpm
a381269b3e2fc43fda59e4d08aef57ae
source rpm:
ftp://ftp.suse.com/pub/suse/ppc/update/7.3/zq1/wuftpd-2.6.0-277.src.rpm
7cacb696a88e57a843402a796212aee6
SuSE-7.1
ftp://ftp.suse.com/pub/suse/ppc/update/7.1/n2/wuftpd-2.6.0-277.ppc.rpm
bfc39be2c09323d96f974fdd0c73fda1
source rpm:
ftp://ftp.suse.com/pub/suse/ppc/update/7.1/zq1/wuftpd-2.6.0-277.src.rpm
e2681b2ed4801ce14b5dfb926480ac51
SuSE-7.0
ftp://ftp.suse.com/pub/suse/ppc/update/7.0/n1/wuftpd-2.6.0-279.ppc.rpm
19f989e637fd9b6fa652f8a4014bb7b1
source rpm:
ftp://ftp.suse.com/pub/suse/ppc/update/7.0/zq1/wuftpd-2.6.0-279.src.rpm
76c493a915691c51a2481f0925e8ce39
SuSE-6.4
ftp://ftp.suse.com/pub/suse/ppc/update/6.4/n1/wuftpd-2.6.0-278.ppc.rpm
ad29cf172bbd03a5e1f301cf6b9404e5
source rpm:
ftp://ftp.suse.com/pub/suse/ppc/update/6.4/zq1/wuftpd-2.6.0-278.src.rpm
82338702692eba599d8c3d242aff3d1a
MandrakeSoft
MandrakeSoft has developed a patch for the problem, fixed packages
will be made available shortly.
Turbo Linux
Contact Turbo-linux for patch information and fixed packages.
Debian Linux
Debian has developed a patch for the problem, fixed packages will be made available shortly.
Wirex Inmunix
WireX has developed a patch for the problem, fixed packages will be made available shortly.
Workaround:
To prevent exploitation of this bug it is advised to disable anonymous FTP access until patches are applied. Notice that legit users with FTP accounts can still exploit the problem even if anonymous access is disabled. If legit ftp accoutn posse a security risk, FTP service should be disabled completly until fixed packages are deployed.
Vendors notified on: November 14th, 2001
Credits:
This vulnerability was initially reported to the vuln-dev mailing list at SecurityFocus.com by Matt Power from Bindview Corp. on April 30th, 2001. At that moment, it was thought as a not exploitable bug and no further research was conducted.
The bug was re-discovered independantly by Core Security Technologies and confirmed to be exploitable on Nov. 1st, 2001
This advisory was drafted with the aid of the Vulnerability Help team at SecurityFocus.com.
We would like to thank the VulnHelp Team, CERT,the WU-ftpd development team and the Linux vendors for their efforts trying to coordinate the release of information and availability of fixes.
Technical Description - Exploit/Concept Code:
Tests were performed using wu-ftp server versions 2.6.1 and 2.7.0 snapshots
WU-FTPD server features globbing capabilities, allowing a user to search pathnames matching patterns according to the rules used by the shell. The feature does not use the glibc implementation of the glob() function, instead it implements its own in the the glob.c file
This implementation fails to set the globerr variable under certain circunstances, bypassing error checking after the call, and trying to free an uninitialized memory address. This memory address is located in the process heap and can be manipulated by the user, issuing especially crafted commands beforehand to the server. This issue was found twice in the source code.
The handling of the globbing metacharacters is done by the ftpglob() function included in the glob.c file. The function is called for example from ftpcmd.y line 1277 and line 1303 while processing pathnames for restricted and non-restricted users beggining with a '/' or a '~'
character respectively.
if (restricted_user && logged_in && $1 && strncmp($1, "/", 1) == 0){
[...]
globlist = ftpglob(t);
[...]
}
else if (logged_in && $1 && strncmp($1, "~", 1) == 0) {
char **globlist;
globlist = ftpglob($1);
[...]
}
After that, the variable globerr is checked to handle any possible error that could had happened during the globbing process, setting this variable is responsability of the ftpglob() function.
Under certain circunstances not properly handled by the function, globerr is not set even though an error condition is present
Being not initialized explicitly, globlist contains what was in the heap before, which can be properly set with specially crafted requests to the server.
As the globerr was not set properly, the function attempts to free
the provided pointer in ftpcmd.y line 1282 and line 1288.
if (globerr) {
reply(550, globerr);
$$ = NULL;
if (globlist) {
blkfree(globlist);
free((char *) globlist);
}
}
else if (globlist) {
$$ = *globlist;
blkfree(&globlist[1]);
free((char *) globlist);
}
As shown, during the processing of a globbing pattern, the Wu-Ftpd implementation creates a list of the files that match.
The memory where this data is stored is on the heap, allocated using malloc(). The globbing function simply returns a pointer to the list. It is up to the calling functions to free the allocated memory.
If an error occurs processing the pattern, memory will not be allocated and a variable indicating this should be set.
The calling functions must check the value of this variable before attempting to use the globbed filenames (and later freeing the memory).
Under certain circumstances, the globbing function does not set this variable when an error occurs. As a result of this, Wu-Ftpd will eventually attempt to free uninitialized memory.
If this region of memory contained user-controllable data before the free call, it is possible to have an arbitrary word in memory overwritten with an arbitrary value. This can lead to execution of arbitrary code if function pointers or return addresses are overwritten.
Details of hwo to exploit this type of problems are in the public domain and can be found in Phrack Magazine #57 article 9.
Unsuccessful explotation of the problem does not lead to denial of service attacks as the ftp server continues normal execution, only the thread handling the request fails, helping the attacker to success.
The following excerpt is a sample verification of the existence of the problem:
ftp> open localhost
Connected to localhost (127.0.0.1).
220 sasha FTP server (Version wu-2.6.1-18) ready.
Name (localhost:root): anonymous
331 Guest login ok, send your complete e-mail address as password.
Password:
230 Guest login ok, access restrictions apply.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> ls ~{
227 Entering Passive Mode (127,0,0,1,241,205)
421 Service not available, remote server has closed connection
1405 ? S 0:00 ftpd: accepting connections on port 21
7611 tty3 S 1:29 gdb /usr/sbin/wu.ftpd
26256 ? S 0:00 ftpd:
sasha:anonymous/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
26265 tty3 R 0:00 bash -c ps ax | grep ftpd
(gdb) at 26256
Attaching to program: /usr/sbin/wu.ftpd, process 26256
Symbols already loaded for /lib/libcrypt.so.1
Symbols already loaded for /lib/libnsl.so.1
Symbols already loaded for /lib/libresolv.so.2
Symbols already loaded for /lib/libpam.so.0
Symbols already loaded for /lib/libdl.so.2
Symbols already loaded for /lib/i686/libc.so.6
Symbols already loaded for /lib/ld-linux.so.2
Symbols already loaded for /lib/libnss_files.so.2
Symbols already loaded for /lib/libnss_nisplus.so.2
Symbols already loaded for /lib/libnss_nis.so.2
0x40165544 in __libc_read () from /lib/i686/libc.so.6
(gdb) c
Continuing.
Program received signal SIGSEGV, Segmentation fault.
__libc_free (mem=0x61616161) at malloc.c:3136
3136 in malloc.c
Note that the segmentation fault is generated because the program is trying to free() a user provided (and in this case invalid) memory chunk referenced by the value 0x61616161 (or its ASCII equivalent 'aaaa', sent earlier in the session as the user password), this should be enough hint on the existence and exploitability of the bug
DISCLAIMER:
The contents of this advisory are copyright (c) 2001 CORE Security Technologies and may be distributed freely provided that no fee is charged for this distribution and proper credit is given.
$Id: WUFTPD_free_advisory.txt,v 1.6 2001/11/29 17:13:20 iarce Exp $