#writeup Articles

[picoctf19] TCalc Writeup

TCalc was a pwnable challenge during the recent Hack.lu CTF 2019. It was worth 381 points and rated medium. As all somewhat more difficult exploit challenges, it was a heap challenge. Somewhat unusual was the usage of libc version 2.30, which I haven't seen much in CTFs. The bug was a very fascinating programming error resulting in an OOB array access that could be used to arbitrary free. This write-up will try to not only describe the solution but also the pitfalls and things that didn't work.

Read More

[picoctf19] Ghostdiary

Ghostdiary was a heap exploit challenge during the recent PicoCTF. The challenge was worth 500 points, i.e. it was one of the "big three" exploit challenges this year. It has the most solves out of the three, but was also unlocked from the beginning. Which means that probably a lot of people tried it who got distracted or stuck at a later point before unlocking the rest. It was one of the more "traditional" challenges. The technique used to exploit it was a nullbyte overflow to cause backwards coalescing, abusing overlapping chunks to overwrite FD and gain code execution by overwriting malloc_hook.

Read More