Lab 01 - Introduction


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


You will solve this lab inside a virtual machine on openstack:

  1. Log in with your LDAP credentials
  2. Create a RSA key pair on (ssh; ssh-keygen -t rsa -b 4096 -C “”)
  3. Make sure you have the public key configured on openstack in Project → Compute → Key Pairs
    • Passphrase authentication will be disabled on the SSH server
    • The key that you provide will be automatically registered in .ssh/authorized_keys
  4. Create a new Instance with the following parameters:
    • Flavor: m1.small
    • Instance Boot Source: Boot from image
    • Source (Image): ISC 2020
    • Network: vlan9
    • Key Pair: the one you just added
      • NOTE: if you have only one key pair configured, it will be chosen by default; otherwise, make sure you don't skip this step
  5. From the fep console (ssh) login into the newly created VM (ssh student@VM-IP)

CTF local tasks

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

01. [10p]B64 encoding

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

02. [10p]EXIF

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

03. [10p]From Manchester with love

04. [10p]Corrupted file

  • The header seems to be damaged…

Up for more?

OS Management

05. [10p]Web server & console browser

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

06. [10p]Disk space & usage

  • 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

Program compilation tools

07. [10p]Program compilation

  • 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)

08. [10p]Static compilation

  • 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 libidn11-dev librtmp-dev libssl-dev libcrypto++-dev libkrb5-dev libldap2-dev libnghttp2-dev libpsl-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 ;)

09. [10p]Traffic sniffing

  • 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.

10. [10p]Logging & Auditing

  • Write an iptables rule that logs all the traffic generated by curl.


11. [10p]Feedback

Please take a minute to fill in the feedback form for this lab.

isc/labs/01.txt · Last modified: 2022/03/07 07:27 by florin.stancu
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