CVE-2025-21896
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk10th percentile - higher than 10% of all known CVEs
Summary
In the Linux kernel FUSE filesystem, the switch to new folio-based readahead code caused the folio reference to be dropped after locking. In splice responses, where the old folio is removed and replaced, the missing reference leads to a use-after-free (UAF).
Risk Assessment
The vulnerability can cause system crashes or potentially privilege escalation due to accessing freed memory during splice operations in FUSE.
Recommendation
Apply the Linux kernel patch that reverts to __readahead_folio() in FUSE to maintain the folio reference throughout readahead.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: fuse: revert back to __readahead_folio() for readahead In commit 3eab9d7bc2f4 ("fuse: convert readahead to use folios"), the logic was converted to using the new folio readahead code, which drops the reference on the folio once it is locked, using an inferred reference on the folio. Previously we held a reference on the folio for the entire duration of the readpages call. This is fine, however for the case for splice pipe responses where we will remove the old folio and splice in the new folio (see fuse_try_move_page()), we assume that there is a reference held on the folio for ap->folios, which is no longer the case. To fix this, revert back to __readahead_folio() which allows us to hold the reference on the folio for the duration of readpages until either we drop the reference ourselves in fuse_readpages_end() or the reference is dropped after it's replaced in the page cache in the splice case. This will fix the UAF bug that was reported.