It seems there was the potential risk that insufficient validation could allow reading arbitrary server files, which indeed poses a security risk.
However, my understanding is that this could be exploited only by authenticated users with permission to add new media. Not like that’s a risk to ignore, but it’s not like it could be exploited by anyone on the Internet.
Yeah, the key seems to be in the comments from one of the changes: https://github.com/jellyfin/jellyfin/commit/0581cd661021752e5063e338c718f211c8929310#diff-bcc2125e56d5738b4778802ac650ca47719845aeee582f3b5c9b46af82ea9979R1176-R1180
It seems there was the potential risk that insufficient validation could allow reading arbitrary server files, which indeed poses a security risk.
However, my understanding is that this could be exploited only by authenticated users with permission to add new media. Not like that’s a risk to ignore, but it’s not like it could be exploited by anyone on the Internet.