Found the error Not allowed to load local resource: file:///etc/passwd while looking at infosec.pub’s communities page. There’s a community called “ignore me” that adds a few image tags trying to steal your passwd file.
You have to be extremely poorly configured for this to work, but the red flags you see should keep you on your toes for the red flags you don’t.
While this is concerning, I wonder what the author(s) of this were thinking would happen. I assume it’s supposed to be an attempt at stealing the server’s passwords, since I at least know of no browser that freely allows access to local files.
FWIW,
/etc/passwditself contains no passwords (the name exists for historical reasons) but it definitely is a globally accessible file that can give you clues about the target system. Given this, it’s more likely the user is attempting to find out if arbitrary disk reads are possible by using a well known path on many servers.