Publications

HTB Business CTF Write-ups

02/08/2021 Synacktiv participated in the first edition of the HackTheBox Business CTF, which took place from the 23rd to the 25th of July. The event included multiple categories: pwn, crypto, reverse, forensic, cloud, web and fullpwn (standard HTB boxes). We managed to get 2nd place after a fierce competition. We had quite a lot of fun so we decided to publish write-ups of the most interesting challenges we solved.

Writing a (toy) symbolic interpreter, and solving challenges, part 4

30/07/2021 This is the last part of series, where we solve the challenge using our symbolic interpreter, and an external SMT solver. Huge success!

Writing a (toy) symbolic interpreter, and solving challenges, part 3

28/07/2021 In this installment, we turn the concrete interpreter into a symbolic interpreter. How exciting!

Writing a (toy) symbolic interpreter, and solving challenges, part 2

23/07/2021 In the second part of this series, we write a concrete interpreter for a subset of WebAssembly.

Writing a (toy) symbolic interpreter, and solving challenges, part 1

19/07/2021 Writing a symbolic interpreter, and wiring it to a solver in order to solve reverse engineering challenges (or other uses), might seem like a daunting task. Even simply using an existing symbolic interpretation framework is far from easy when one has no experience in it. This serie of articles will describe, throughout the summer, how such an engine is built, and showcase implementation tricks and some trade offs to be aware off. Do not worry, the interpreter will be kept as simple as possible though! In the end, we...

Exploitation of a double free vulnerability in Ubuntu shiftfs driver (CVE-2021-3492)

13/07/2021 This year again, the international contest Pwn2Own Vancouver took place in the beginning of April. Among the different categories, two major operating systems were suggested for the Local Escalation of Privilege category (LPE): Linux (Ubuntu) and Windows 10. This article describes how a Ubuntu kernel vulnerability was found and exploited during this contest allowing to gain root access from an unprivileged user.

Baking Mojolicious cookies

01/06/2021 Mojolicious is a Perl framework for web development we have recently encountered during one of our missions. Mojolicious handles cookies using a JSON string signed using HMAC-SHA1. The format reminds JWT. This article describes how the cookie signature is done by Mojolicious and how to crack it in order to generated valid cookies.

Playing with ImageTragick like it's 2016

28/05/2021 You probably already have encountered document converting features that deal with ImageMagick during engagements but for some reason you were not able to exploit them. This article will mention some techniques that could be used when an older version of ImageMagick is targeted. Spoiler alert: this is not new.

RM -RF IS THE ROOT OF ALL EVIL

27/05/2021 There are some days where things do not go your way. And there are some other days where they go catastrophically wrong. Several months ago, I had the unfortunate experience of wiping 2 years of my work. This blogpost explains why this tragedy happened and what I did to recover some critical data from the ashes of my SSD.

Kubernetes namespaces isolation - what it is, what it isn't, life, universe and everything

26/03/2021 When speaking about Cloud, containers, orchestration and that kind of things, Kubernetes is the name that comes to mind. We meet it in a lot of situations ranging from microservices implementation to user oriented self service hosting. But developers don't always understand the limits of the system and the mechanisms it implements. In particular, we commonly encounter misunderstanding about namespaces isolation. Time to bring some light in this darkness.