CVE-2026-89841 f2fs: only redirty pinned folios in redirty_blocks
A reference counting error in the f2fs filesystem can cause a use-after-free condition, leading to kernel crashes and denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89841?
CVE-2026-89841 is a high-severity use after free vulnerability in Linux, published on 16 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
f2fs: only redirty pinned folios in redirty_blocks
redirty_blocks() pins folios with read_cache_folio() and then walks the same range again with filemap_lock_folio() to redirty them and drop the references it took.
Commit 5951fee46bef ("f2fs: Use a folio in redirty_blocks()") changed the second pass to a do/while loop. If read_cache_folio() fails before anything is pinned, page_idx does not advance but the cleanup loop still runs once.
If readahead has already populated the failed folio in page cache, that extra iteration finds it and folio_put_refs(folio, 2) drops one reference too many. Later drop_caches or reclaim can then report "BUG: Bad page state".
Only redirty the range that was pinned successfully.
Which versions are affected by CVE-2026-89841?
How do I fix CVE-2026-89841?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-89841 being exploited?
There is no known exploitation of CVE-2026-89841 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-89841, DEBIAN-CVE-2026-89841, GHSA-9c6f-r39g-mhg4, UBUNTU-CVE-2026-89841.