Collisions in this hash function have been proven in the following paper: [https://eprint.iacr.org/2005/403.pdf](https://eprint.iacr.org/2005/403.pdf). For the sake of completeness, however, I have briefly explained one of the collisions: the "appending" case.

Original writeup (https://zeyu2001.gitbook.io/ctfs/2021/zh3ro-ctf-v2/chaos).