CVE-2025-37999 is a medium-severity vulnerability in the Linux kernel's EROFS filesystem code. It involves improper handling of folio references when bio_add_folio() fails, leading to a folio being locked indefinitely. This causes processes waiting on the folio to hang, resulting in a denial of service. The issue was introduced by a commit supporting unencoded inodes and became exploitable after a later commit reduced bio array capacity. The fix involves calling erofs_onlinefolio_split() only after bio_add_folio() succeeds to ensure proper folio reference counting.