Attacker needs to know the unix username of the victim.
Browsers ask the user for permission on redirects to custom schemes.
However, the initial current working directory (CWD) of applications started by GNOME (e.g., using Alt+F2 or dock shortcuts) is the user’s home directory. As a result, the CWD of Chrome and Firefox is also set to the user’s home directory. We can abuse this behavior to point to the victim’s Downloads folder and bypass the first condition.
Ouch, how did this happen, and why have patches sat unreviewed?
Here they talk about the issue and its limitations and it seems they missed the workaround mentioned below in the writeup:
https://gitlab.gnome.org/GNOME/yelp/-/issues/221#note_2392999
https://gist.github.com/parrot409/e970b155358d45b298d7024edd9b17f2