Note: This is a mirror of the Medium blogpost.


After discovering relatively straightforward memory corruption vulnerabilities in tiny DBF parsers and Apache OpenOffice, I wanted to cast my net wider. By searching for DBF-related vulnerabilities in Microsoft's desktop database engines, I took one step towards the deep end of the fuzzing pool. I could no longer rely on source code review and dumb fuzzing; this time, I applied black-box coverage-based fuzzing with a dash of reverse engineering. My colleague Hui Yi has written several fantastic articles on fuzzing with WinAFL and DynamoRIO; I hope this article provides a practical application of those techniques to real vulnerabilities.


Note: This is a mirror of the Medium blogpost.


Venturing out into the wilderness of vulnerability research can be a daunting task. Coming from a background in primarily web and application security, I had to shift my hacking mindset towards memory corruption vulnerabilities and local attack vectors. This two-part series will share how I got started in vulnerability research by discovering and exploiting code execution zero-days in office applications used by hundreds of millions of people. I will outline my approach to getting started in vulnerability research including dumb fuzzing, coverage-guided fuzzing, reverse engineering, and source code review. I will also discuss some management aspects of vulnerability research such as CVE assignment and responsible disclosure.

In part two, I will disclose additional vulnerabilities that I discovered via coverage-guided fuzzing – including CVE-2021-38646: Microsoft Office Access Connectivity Engine Remote Code Execution Vulnerability.


Note: This is the blogpost version of a talk I gave to the National University of Singapore Greyhats club. If you prefer video, you can watch it here:


Now that Mr. Robot and The Matrix are back on Netflix, re-watching them has been a strangely anachronistic experience. On the one hand, so much of what felt fresh and original back then now seems outdated, even cringey. After all, the past few years definitely provided no end of “F SOCIETY” moments, not to mention the hijacking of “red pill”... but the shows stand on their own with some of the most arresting opening scenes I've ever watched.

Matrix Cutscene

Mr Robot Cutscene

With AI well into the technology adoption lifecycle, most of the low-hanging fruits have been plucked – in cybersecurity, antivirus engines have integrated machine learning models on the client and in the cloud, while malicious actors abuse synthetic media generation to execute all kinds of scams and schemes. There's a ton of hype and scaremongering for sure, but still good reason to be concerned.


The Rule of Three

EXP-301 Logo by Offensive Security

The Windows User Mode Exploit Development (EXP-301) course and the accompanying Offensive Security Exploit Developer (OSED) certification is the last of the three courses to be released as part of the Offensive Security Certified Expert – Three (OSCE3) certification. Since the appointment of the new CEO Nina Wang in 2019, Offensive Security has revamped its venerable lineup of courses and certifications, culminating in the new OSCE3 announced at the end of 2020. As I’ve discussed in my Offensive Security Experienced Penetration Tester (OSEP) review, this makes a lot of sense from a marketing and sales strategy standpoint. Although Offensive Security was best known for its no-expiry certifications, it has since retired a number of them, including the old OSCE and more recently Offensive Security Wireless Attacks (OSWP). It has also introduced a number of recurring revenue subscription products such as the Offensive Security Proving Grounds, PWK365, and more. Oh, and it’s raising the price of exam retakes from $150 to $249. These are all great business decisions for Offensive Security, but for the regular cybersecurity professional, is the EXP-301/OSED worth it?



The Peach protocol fuzzer was a well-known protocol fuzzer whose parent company — Peach Tech — was acquired in 2020 by GitLab. While Peach Tech had previously released a Community Edition of Peach fuzzer, it lacked many key features and updates found in the commercial editions. Fortunately, GitLab has open-sourced the core protocol fuzzing engine of Peach under the name “GitLab Protocol Fuzzer Community Edition,” allowing anyone to build and deploy it. For simplicity, I will refer to the new open-sourced version as Peach Fuzzer.


As expected of an early-stage project, the build process is complicated and not well-documented. In addition, first-time users may have trouble understanding how to use the fuzzer. Moreover, GitLab's open-sourced version still lacks important resources such as fuzzing templates, which means you will have to write them on your own.

To that end, this article aims to demonstrate an end-to-end application of Peach Fuzzer, from build to deployment. Look out for a subsequent article where I will touch on the full workflow of finding and exploiting vulnerabilities using Peach Fuzzer.


Good Things Come in Threes

In August last year, Offensive Security announced that it was retiring the long-standing Offensive Security Certified Expert (OSCE) certification and replacing it with three courses, each with their own certification. If you get all three, you are also awarded the new Offensive Security Certified Expert – Three (OSCE3) certification.

OSCE3 by Offensive Security

While this is undoubtedly a great business decision by Offensive Security – the market loves bundles – how useful are these courses for security professionals? The first of the three courses, Advanced Web Attacks and Exploitation (WEB-300)/Offensive Security Web Expert (OSWE), was already released at that time and is a known quantity. In October 2020, Offensive Security released the Evasion Techniques and Breaching Defenses (PEN-300) course that comes with the Offensive Security Experienced Penetration Tester (OSEP) certification and more recently released Windows User Mode Exploit Development (EXP-301)/Offensive Security Exploit Developer (OSED). The three courses target specific domains and therefore are relevant to different roles in offensive security.

As I had already achieved the OSWE in 2019, I took the 60-day OSEP package from January to February 2021. At the time of writing, this costs $1299. PEN-300/OSEP teaches Red Team skills – if your job involves network penetration (such as through phishing emails) and subsequently pivoting through Active Directory environments with the occasional Linux server, this is the course for you. If you are mostly working on application penetration testing (think web and mobile apps), OSWE is a better fit. And if you are doing vulnerability research in binaries, OSED will build that foundation.

Overall, I felt that the OSEP was worth the price of admission given the sheer amount of content it throws at you, as well as the excellent labs that will solidify your learning-by-doing. Here's my review along with some tips and tricks to maximize your OSEP experience.


Late last year, I was invited to Facebook's Bountycon event, which is an invitation-only application security conference with a live-hacking segment. Although participants could submit vulnerabilities for any Facebook asset, Facebook invited us to focus on Facebook Gaming. Having previously tested Facebook's assets, I knew it was going to be a tough challenge. Their security controls have only gotten tougher over the years – even simple vulnerabilities such as cross-site scripting are hard to come by, which is why they pay out so much for those. As such, top white hat hackers tend to approach Facebook from a third-party software angle, such as Orange Tsai's well-known MobileIron MDM exploits.

Given my limited time (I also started late due to an administrative issue), I decided to stay away from full-scale vulnerability research and focussed on simple audits of Facebook Gaming's access controls. However, both the mobile and web applications were well-secured, as one would expect. After a bit of digging, I came across Facebook Gameroom, a Windows-native client for playing Facebook games. I embarked on an illuminating journey of applying offensive reverse engineering to a native desktop application.



GovTech's Cyber Security Group recently organised the STACK the Flags Cybersecurity Capture-the-Flag (CTF) competition from 4th to 6th December 2020. For the web domain, my team wanted to build challenges that addressed real-world issues we have encountered during penetration testing of government web applications and commercial off-the-shelf products.

From my experience, a significant number of vulnerabilities arise from developers' lack of familiarity with third-party libraries that they use in their code. If these libraries are compromised by malicious actors or applied in an insecure manner, developers can unknowingly introduce devastating weaknesses in their applications. The SolarWinds supply chain attack is a prime example of this.


Incident reported!

I recently participated in FireEye's seventh annual Flare-On Challenge, a reverse engineering and malware analysis Capture The Flag (CTF) competition. Out of the 11 challenges ranging from typical executables to games written in exotic programming languages, I liked Challenge 7 the best. It featured a network traffic capture of a security breach with two stages. Having mostly worked in the red team, I enjoyed the opportunity to investigate Metasploit internals and shellcode from the perspective of a blue team.

As a beginner in malware analysis, I often found myself confused by tutorials that went from A to Z without explaining the thought process or tools used to get there. I hope that my detailed walkthrough of challenge 7 will be useful for other newcomers.


Introduction: Red Alert!

Last month, the Centre for Strategic Infocomm Technologies (CSIT) invited local cybersecurity enthusiasts to tackle the InfoSecurity Challenge (TISC). The Challenge was organized in a capture-the-flag format, with 6 cybersecurity and programming challenges of increasing difficulty unlocked one after another.

On New Year’s Eve, hackers from the PALINDROME group launched a ransomware attack on a major finance company and encrypted some of its critical data servers. Your mission is to complete a series of tasks to recover as much data as possible to prevent the company from having to give in to PALINDROME's demand. The tasks will increase in difficulty as you go along so be prepared to put up the fight of your life.

With this exciting introduction, I tackled a series of difficult problems that encompassed reverse engineering, binary exploitation, and cryptography. This took me far out of my comfort zone of application security, but since I wanted to build my skills in those areas, it was a welcome challenge.


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