Wednesday, November 6, 2013

hashed known_hosts

le sigh. by default on my linux boxes, known_hosts are hashed. cool if there's a worm worming around using your ssh known_hosts or there's a cracker that wants access to your pubkeyed stuff. but what do you do when someone leaves? sure you rotate passwords, sure you guard your gateways. but what about all of those pubkeyed systems? 

this is useful:
http://blog.rootshell.be/2010/11/03/bruteforcing-ssh-known_hosts-files/
http://blog.rootshell.be/wp-content/uploads/2010/11/known_hosts_bruteforcer.pl.txt

make sure your path to perl is correct and you've installed those modules (cpan install is your friend)


#!/usr/bin/perl
#
# SSH known_hosts file bruteforcer
#
# v1.0 - Xavier Mertens 
#
# This Perl script read a SSH known_host file containing hashed hosts and try to find hostnames
# or IP addresses
#
# 20101103 : Created
#
# Todo
# ----
# - Support for IPv6 addresses
# - Increase performances
#

use Getopt::Std;
use Digest::HMAC_SHA1;
use MIME::Base64;
use Net::IP;

$MAXLEN = 8;				# Maximum hostnames length to check
$MAXIP  = 4294967296; # 2^32		# The whole IPv4 space

@saltStr   = ();
@base64Str = ();
$idx       = 0;

# Process the arguments
getopts("d:f:l:s:ivh", \%options);

# Some help is sometimes useful
if ($options{h}) {
	print <   Specify a domain name to append to hostnames (default: none)
  -f      Specify the known_hosts file to bruteforce (default: $HOME/.ssh/known_hosts)
  -i            Bruteforce IP addresses (default: hostnames)
  -l   Specify the hostname maximum length (default: 8)
  -s    Specify an initial IP address or password (default: none)
  -v            Verbose output
  -h            Print this help, then exit
EOF
	exit;
}

# SSH Keyfile to process (default: $HOME/.ssh/known_hosts)
$knownhostFile = ($options{f} ne "") ? $options{f} : $ENV{HOME} . "/.ssh/known_hosts";
if (! -r $knownhostFile) {
	print STDERR "Cannot read file $knownhostFile ...\n";
	exit 1;
}

# Max password length (default: 8)
$passwordLen = ($options{l} ne "") ? $options{l} : $MAXLEN;
if ($passwordLen < 1 || $passwordLen > 30) {
	print STDERR "Invalid maximum password length: $passwordLen ...\n";
	exit 1;
}

# Domain name to append
$domainName = $options{d};

# Verbose mode
$verbose = ($options{v}) ? 1 : 0;

# IP address mode
$ipMode = ($options{i}) ? 1 : 0;

# Starting IP or password?
# To increase the speed of run the script across multiple computers,
# an initial hostname or IP address can be given
$initialStr = $options{s};

# First read the known_hosts file and populate the lists
# Only hashed hosts are processed
($verbose) && print STDERR "Reading hashes from $knownhostFile ...\n";
open(HOSTFILE, "$knownhostFile") || die "Cannot open $knownhostFile";
while() {
	($hostHash, $keyType, $publicKey) = split(/ /);
	if ($hostHash =~ m/\|1\|/) {
		($dummy, $one, $saltStr[$idx], $base64Str[$idx]) = split(/\|/, $hostHash);
		$idx++;
	}
}
close(HOSTFILE);

# ---------
# Main Loop
# ---------

$loops=0;
while(1) {
	if ($ipMode) {
		# Generate an IP address using the main loop counter
		# Don't go beyond the IPv4 scope (2^32 addresses)
		if ($loops > $MAXIP) {
			print "Done.\n";
			exit 0;
		}

		# If we have an initial IP, check the syntax and use it
		if ($initialStr ne "") {
			my $ip = new Net::IP($initialStr);
			$initialIP = $ip->intip();
		}
		else {
			$initialIP = 0;
		}
		$tmpHost = sprintf("%vd", pack("N", $loops + $initialIP));
	}
	else {
		# Generate a temporary hostname (starting with an initial value if provided)
		$tmpHost = generateHostname($initialStr);
		if (length($tmpHost) > $passwordLen) {
			print "Done.\n";
			exit 0;
		}

		# Append the domain name if provided
		if ($domainName) {
			$tmpHost = $tmpHost . "." . $domainName;
		}
	}

	# In verbose mode, display a line every 1000 attempts
	($verbose) && (($loops % 1000) == 0) && print STDERR "Testing: $tmpHost ($loops probes) ...\n";
	
	if ($line = searchHash($tmpHost)) {
		printf("*** Found host: %s (line %d) ***\n", $tmpHost, $line + 1);
	}

	$loops++;
}

#
# Generate SHA1 hashes of a hostname/IP and compare it to the available hashes
# Returns the line index of the initial known_hosts file
#
sub searchHash() {
	$host = shift;
	($host) || return 0;

	# Process the list containing our hashes
	# For each one, generate a new hash and compare it
	for ($i = 0; $i < scalar(@saltStr); $i++) {
		$decoded = decode_base64($saltStr[$i]);
		$hmac = Digest::HMAC_SHA1->new($decoded);
		$hmac->add($host);
		$digest = $hmac->b64digest;
		$digest .= "="; # Quick fix ;-)
		if ($digest eq $base64Str[$i]) {
			return $i;
		}
	}
	return 0;
}

#
# Generate a hostname based on a given set of allowed caracters
# This sub-routine is based on:
# bruteforce 0.01 alpha
# Written by Tony Bhimani
# (C) Copyright 2004
# http://www.xenocafe.com
#

sub generateHostname {
	$initialPwd = shift;

	$alphabet = "abcdefghijklmnopqrstuvwxyz0123456789-";
	@tmpPwd = ();
	$firstChar = substr($alphabet, 0, 1);
	$lastChar = substr($alphabet, length($alphabet)-1, 1);

	# If an initial password is provided, start with this one
	if ($initialPwd ne "" && $currentPwd eq "") {
		$currentPwd = $initialPwd;
		return $currentPwd;
	}

	# No password so start with the first character in our alphabet
	if ($currentPwd eq "") {
		$currentPwd= $firstChar;
		return $currentPwd;
	}

	# If the current password is all of the last character in the alphabet
	# then reset it with the first character of the alphabet plus 1 length greater
	if ($currentPwd eq fillString(length($currentPwd), $lastChar)) {
 		$currentPwd = fillString(length($currentPwd) + 1, $firstChar);
		return $currentPwd;
	}
  
	# Convert the password to an array
	@tmpPwd = split(//, $currentPwd);
  
	# Get the length of the password - 1 (zero based index)
	$x = @tmpPwd - 1;

	# This portion adjusts the characters
	# We go through the array starting with the end of the array and work our way backwords
	# if the character is the last one in the alphabet, we change it to the first character
	# then move to the next array character
	# if we aren't looking at the last alphabet character then we change the array character
	# to the next higher value and exit the loop
	while (1) {
		$iTemp = getPos($alphabet, $tmpPwd[$x]);
  
		if ($iTemp == getPos($alphabet, $lastChar)) {
			@tmpPwd[$x] = $firstChar;
			$x--;
		} else {
			@tmpPwd[$x] = substr($alphabet, $iTemp + 1, 1);
			last;
		}
	}
  
	# Convert the array back into a string and return the new password to try
	$currentPwd = join("", @tmpPwd);
    
	return $currentPwd;
}

#
# Fill a string with the same caracter
#

sub fillString {
	my ($len, $char) = (shift, shift);
	$str = "";
	for ($i=0; $i<$len; $i++) {
		$str .= $char;
	}
	return $str;
}

#
# Return the position of a caracter in a string
#

sub getPos {
	my ($alphabet, $char) = (shift, shift);
	for ($i=0; $i
# Eof 
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