The ALLES! CTF (ctftime.org) took place from 04/09/2020, 16:00 UTC to 06/09/2020, 19:00 UTC with a variety of interesting, creative challenges.
Within this article I want to share my writeup on the two challenges Actual ASLR 1 and 2, which were authored by LiveOverflow. What I especially liked about the challenge(s) is that you could make progression step by step even getting a first flag on the way to a full shell, which grants access to the second flag.
The article is divided into the following sections:
One of my goals for this year is to spend a little bit more of my spare time on real world applications. Doing so I took a look at the remote desktop application AnyDesk, which seems to quickly raise in popularity not only because of COVID-19. AnyDesk is available for a variety of operating systems including Windows, Linux, Android and iOS. By reversing and fuzzing the Linux version 5.5.2 of the application I was able to find a format string vulnerability, which can be used to gain Remote Code Execution (RCE) by sending a single UDP packet to the target machine. AnyDesk took the issue very seriously. They released a patch only three days after my notification (5.5.3) and paid me a bounty of 5.000 EUR. The vulnerability is tracked as CVE-2020-13160. Within this article I want to share all steps, which were involved in finding the vulnerability, understanding the bug and developing the RCE exploit. The article is divided into the following sections: