OverTheWire Leviathan – Level 2

When listing leviathan2‘s user directory we again find an ELF 32-bit executable, printfile, with the SETUID bit set.

ltrace output:

leviathan2@leviathan:~$ ltrace ./printfile '/etc/leviathan_pass/leviathan2'
 __libc_start_main(0x804852b, 2, 0xffffd764, 0x8048610 
 access("/etc/leviathan_pass/leviathan2", 4)      = 0
 snprintf("/bin/cat /etc/leviathan_pass/lev"…, 511, "/bin/cat %s", "/etc/leviathan_pass/leviathan2") = 39
 geteuid()                                        = 12002
 geteuid()                                        = 12002
 setreuid(12002, 12002)                           = 0
 system("/bin/cat /etc/leviathan_pass/lev"…ougahZi8Ta
 --- SIGCHLD (Child exited) ---
 <… system resumed> )                           = 0
 +++ exited (status 0) +++
Continue reading “OverTheWire Leviathan – Level 2”

OverTheWire Leviathan – Level 1

Listing the directory of user leviathan1 reveals a ELF 32-bit executable with it’s SETUID bit set.

leviathan1@leviathan:~$ ls -la
 total 28
 drwxr-xr-x  2 root       root       4096 Oct 29  2018 .
 drwxr-xr-x 10 root       root       4096 Oct 29  2018 ..
 -rw-r--r--  1 root       root        220 May 15  2017 .bash_logout
 -rw-r--r--  1 root       root       3526 May 15  2017 .bashrc
 -r-sr-x---  1 leviathan2 leviathan1 7452 Oct 29  2018 check
 -rw-r--r--  1 root       root        675 May 15  2017 .profile
 leviathan1@leviathan:~$ file check
 check: setuid ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=c735f6f3a3a94adcad8407cc0fda40496fd765dd, not stripped
Continue reading “OverTheWire Leviathan – Level 1”

Port Knocking & Knockd Configuration

What is port knocking? Port knocking is a method of securing external facing services – explicitly blocked by firewall rules – by enabling firewall access only in the event that a correct sequence of connection attempts to random predetermined ports is attempted. Upon receipt of a correct sequence of connection attempts, the firewall rules are modified on the requested server, temporarily enabling access to the service for the requesting client.

The popular port knocking tool, Knockd, allows users to customize a variety of options to tweak their Knockd deployment. A user might customize the length of the port knocking sequence, the ports specified, the protocol (TCP/UDP), the packet’s flag type(s) (syn, ack, fin…), timeout period, and even an alternate sequence of ports to close the connection.

Before we jump into defining the steps needed to install a Knockd instance, let’s see it in action…

Preliminary Nmap Scan

To start, I have a CentOS machine on my local network (IP – with an SSH server configured and enabled on port 22. Knockd has been enabled and a firewall rule has been configured to block all incoming traffic destined for port 22 (ssh).

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CentOS Router Configuration for a Web Server

I wanted to follow up a previous post, where I described the process of configuring a CentOS router for the intention of creating a separate, internal LAN. There we simply deployed a router to separate an external WAN from our LAN and configured the router to pass along all traffic between the two interfaces.

This time I wanted to deploy a router for the purpose of serving content from an internal web server, to an external LAN or WAN.

While this is something that I used recently for a local hackathon, I believe it has greater “real world” application, and can be modified only slightly to accommodate the deployment of other services or applications.

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CentOS Router: Configuration in Vmware

In preparation for an upcoming hackathon, I began working with CentOS as a means to route traffic between two VMware machines: a ParrotOS machine, and a Metasploitable2 machine – both configured on different subnets.

For this tutorial I used the following:

  • VMware Workstation 15
  • ParrotOS
  • Metasploitable2
  • CentOS (Minimal Installation)

CentOS Router Configuration

First, let’s configure the CentOS router to forward traffic between the ParrotOS machine (residing on network and the Metasploitable2 machine (residing on network

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