CVE-2025-21896 is a use-after-free vulnerability in the Linux kernel's FUSE filesystem readahead implementation. A recent change to use folio-based readahead dropped a necessary reference on folios prematurely, causing a reference to be missing during splice pipe responses. The issue was fixed by reverting to the previous readahead method that maintains the folio reference for the duration of the readpages call, preventing the use-after-free condition.