Upon opening the challenge URL, we can see that the application uses pdflatex to compile the LaTeX code supplied by the user.
In the Typesetting log, we can see that \write18 is enabled.
Let’s see the latex documentation.
Let’s try \immediate\write18{cat /flag.txt} assuming the flag is located at /flag.txt as the previous challenge Merged also has flag at the same location.
We got the flag :)
I did this exact same thing in overleaf.com but it was a docker container and that docker image is isolated and only contain the files related to that particular project. so no use :(
As I already did this in overleaf, I was able to solve this challenge easily and quickly.