Lab 01 - Introduction

• Simple CTF tasks
• Introduction to basic security-related tools
• Simple program compiling tools
• Basics of networking related monitoring tools

You may use the UPB's OpenStack cloud to instantiate a Virtual Machine to be used for this lab! Read these instructions if you wanna know how!.

Download the task archive for this section. Each exercise will have a corresponding folder.

• The flag is in b64.txt. It should look something like this: FLAG{…}.
  • Hint: python3, base64

• The flag is hidden somewhere within this image. Remember its format.
  • Hint: it's not steganography; don't look at the pixels

• Remember RL? Remember Manchester?

• The header seems to be damaged…

Up for more?

• CTFlearn
• OverTheWire
• Cryptopals Challenges
• PicoCTF

• Install and configure apache2 and links. Use the latter to connect to http://localhost
  • Hint: use the distro specific package manager.

• Display the disk space usage for each individual directory (. and .. excluded) in the first two hierarchical levels of /usr/include/ in a human readable format
  • Hint: find, du
• Sort the list in ascending order, by size

• Download the following program and compile it using gcc.
• What is the program intended for?
• Modify the program such that it connects to “http://localhost” (i.e. your local apache server) and prints the response (apache's default HTML test page) to stdout, just like standard curl.
  • Hint: you need to install libcurl's development libraries.
  • Hint: you need some flags for the compiler to know where libcurl is installed (see library's documentation)

• Statically compile the program (but keep a copy of the old, shared executable).
  • Hint: curl-config --static-libs
  • Hint: Note that you'll need even more development libraries: libidn11-dev librtmp-dev libssl-dev libcrypto++-dev libkrb5-dev libldap2-dev libnghttp2-dev libpsl-dev libssh-dev libzstd-dev libbrotli-dev
  • Hint: Getting a pthread-related linker error? Try -lpthread at the end of the gcc command!
• Check the size difference. What does it mean?
  • Hint: ldd
• Uninstall libcurl and see which of the executables successfully run now!
• Reinstall curl again if you need it ;)

• Use the tcpdump suite to save all the traffic from interface ens3/eth0 to a file.
  • Hint: Tcpdump may complain that it has no privileges to write the log file. Use ”-Z student” (man!) to reacquire them.