Ετήσια αρχεία: 2018

NetCat (nc) as a webserver

 στο Bash / GNU/Linux  επισημασμένο με ετικέτα nc / NetCat / webserver Από

Recently, we needed to perform some tests in a network. Specifically, we wanted to check the configuration of a firewall and see what IP are blocked and/or which ports are allowed to go through. To do so, we used NetCat to setup a small web-server to perform our tests.

Netcat (often abbreviated to nc) is a computer networking utility for reading from and writing to network connections using TCP or UDP. Netcat is designed to be a dependable back-end that can be used directly or easily driven by other programs and scripts. At the same time, it is a feature-rich network debugging and investigation tool, since it can produce almost any kind of connection its user could need and has a number of built-in capabilities.

From: https://en.wikipedia.org/wiki/Netcat


while true;
do
  echo -e "HTTP/1.1 200 OK\r\n\r\n<h1>$(hostname) is live</h1>$(date)" | nc -vl -p 5555;
done

or in one line


while true; do echo -e "HTTP/1.1 200 OK\r\n\r\n<h1>$(hostname) is live</h1>$(date)" | nc -vl -p 5555; done

Explanation of code:

  • The above code creates an infinite loop that calls nc in listening mode, we had to do this as nc will terminate as soon as it serves one client.
  • Using echo we create an html 200 response along with a small “webpage”.
  • While generating the webpage, echo -e will execute the commands hostname and date to get the current system values adding them to the resulted text.
  • The resulted text is then piped to nc to be served as a response to any incoming clients.
  • The date and time that nc will show to the client is not the current date and time when visiting the webpage but the one that was when echo was executed.

nc parameters:

  • -v, --verbose Sets the verbosity level and it can be used several times to increase it even further
  • -l, --listen Instructs nc to bind and listen for incoming connections (just like a web-server)
  • -p, --source-portwith port parameter specifies the source port to be used by nc

Missing dependencies for udacity/FCND-Controls C++ project (Flying Car Nanodegree Program)

 στο GNU/Linux  επισημασμένο με ετικέτα cmake / FCND / flying car / freeglut / nanodegree / qt5 / qt5core / udacity Από

While taking the Flying Car Nanodegree Program at the third chapter, named Controls, you will be asked to compile a C++ project and build a controller from https://github.com/udacity/FCND-Controls-CPP. On a standard Fedora installation some packages are missing and you will get an error, to resolve that issue you need to install the following two packages on your system:


sudo dnf install -y qt5-devel freeglut-devel;

 

Without these packages you would get the following errors:

CMake Error at CMakeLists.txt:29 (find_package):
By not providing "FindQt5Core.cmake" in CMAKE_MODULE_PATH this project has
asked CMake to find a package configuration file provided by "Qt5Core", but
CMake did not find one.

Could not find a package configuration file provided by "Qt5Core" with any
of the following names:

Qt5CoreConfig.cmake
qt5core-config.cmake

Add the installation prefix of "Qt5Core" to CMAKE_PREFIX_PATH or set
"Qt5Core_DIR" to a directory containing one of the above files. If
"Qt5Core" provides a separate development package or SDK, be sure it has
been installed.


-- Configuring incomplete, errors occurred!

CMake Error at /usr/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:137 (message):
Could NOT find GLUT (missing: GLUT_glut_LIBRARY GLUT_INCLUDE_DIR)
Call Stack (most recent call first):
/usr/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:378 (_FPHSA_FAILURE_MESSAGE)
/usr/share/cmake/Modules/FindGLUT.cmake:116 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
CMakeLists.txt:34 (find_package)


-- Configuring incomplete, errors occurred!
See also "/home/xeirwn/Downloads/Flying Car/03 - Controls/14 - Control of a 3D Quadrotor/FCND-Controls-CPP/build/CMakeFiles/CMakeOutput.log".

YARA on Fedora

 στο GNU/Linux  επισημασμένο με ετικέτα fedora / yara Από

YARA is a tool aimed at (but not limited to) helping malware researchers to identify and classify malware samples. With YARA you can create descriptions of malware families (or whatever you want to describe) based on textual or binary patterns. Each description, a.k.a rule, consists of a set of strings and a boolean expression which determine its logic.

Recently, we tried to compile YARA on a Fedora 23 GNU/Linux (running through a qubes-os version 3).
As the installation guide is directed towards Ubuntu/Debian users, we soon found out that the installation had some missing dependencies. Below, you will find all the steps we followed to download YARA / install its dependencies and build it enabling as all optional features.


sudo dnf install automake libtool make gcc flex bison jansson-devel jansson openssl openssl-devel file-libs file-devel python-magic python3-magic;

git clone https://github.com/VirusTotal/yara; # Or download a release from: https://github.com/virustotal/yara/releases/tag/v3.8.1

cd yara;

./bootstrap.sh;

./configure --enable-cuckoo --enable-magic --enable-dotnet;

make;

sudo make install;

This information is an extension to the installation guide.

Install Gnome Boxes on Kali Linux

 στο GNU/Linux  επισημασμένο με ετικέτα boxes / debian / gnome / gnome boxes / kali / qemu / ubuntu / usermod Από

Our solution in getting Gnome Boxes to work on Kali Linux (which is a Debian-derived Linux distribution just like Ubuntu) is the following:

First install Gnome Boxes along with all needed virtualization software:


sudo apt-get install -y gnome-boxes qemu-kvm libvirt0 virt-manager bridge-utils;

Then, edit the file /etc/libvirt/qemu.conf to uncomment the following line:

#user = "root"

Finally, restart the host machine and your Gnome Boxes will be ready to use.

Long story

Recently, we were setting up a Kali Linux machine and one of the requirements was to add virtualization support so that the user could execute virtual machines doing.. other stuff. We started by installing gnome-boxes only (hoping that would be enough)


sudo apt-get install -y gnome-boxes;

.. but we got an error:

Boxes cannot access the virtualization backend

Apparently, installing gnome-boxes only, the dependency system did not automatically assume we would need to install an engine to handle the virtual machines, so we had to install the following as well:


sudo apt-get install -y qemu-kvm libvirt0 virt-manager bridge-utils;

After the installation, we tried  to create a new virtual machine but it would fail when we tried to start it. After looking into the logs we found the following useful information:

State: GVIR_DOMAIN_STATE_SHUTOFF

It seems that our user (even if it was root) could not start the QEMU process. To fix this issue we had to modify the file /etc/libvirt/qemu.conf and uncomment the following line:

#user = "root"

from this section

# The user for QEMU processes run by the system instance. It can be
# specified as a user name or as a user id. The qemu driver will try to
# parse this value first as a name and then, if the name doesn't exist,
# as a user id.
#
# Since a sequence of digits is a valid user name, a leading plus sign
# can be used to ensure that a user id will not be interpreted as a user
# name.
#
# Some examples of valid values are:
#
# user = "qemu" # A user named "qemu"
# user = "+0" # Super user (uid=0)
# user = "100" # A user named "100" or a user with uid=100
#
#user = "root"

# The group for QEMU processes run by the system instance. It can be
# specified in a similar way to user.
#group = "root"

After doing this change and restarting the host machine we were able to start and use any virtual machine in Gnome Boxes.

Extra information

In this case, we were using Kali Linux, where people usually operate it using the root account only.
On other installations, like on an Ubuntu installation you would need to handle differently the last step that requires you to edit the /etc/libvirt/qemu.conf file.

Specifically, the best way to handle this issue on a multi-user environment (like Ubuntu) would be to replace the following line:

#group = "root"

with this

group = "kvm"

and then add yourself to the kvm group before restarting the host machine


sudo usermod -a -G kvm $USER;

Doing so, it allows you to enable access to the virtualization services to multiple users of you choice instead of limiting it to one account.