CVE-2026-89644 btrfs: fix extent map leak in NOCOW direct I/O write
A local attacker can trigger a memory leak in the Btrfs filesystem during direct I/O writes, potentially leading to resource exhaustion 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-2026-89644?
CVE-2026-89644 is a memory corruption vulnerability in Linux, published on 11 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:
btrfs: fix extent map leak in NOCOW direct I/O write
btrfs_dio_iomap_begin() calls btrfs_get_extent(), which returns an extent map reference that must be dropped on all exit paths.
For direct writes into a NOCOW range, btrfs_get_blocks_direct_write() keeps using that extent map and asks btrfs_create_dio_extent() to allocate the ordered extent. If that fails, for example because btrfs_alloc_ordered_extent() fails, the function returns the error without dropping the input extent map. The PREALLOC path avoided this by dropping the input extent map before replacing it with the newly created one.
Check the error from btrfs_create_dio_extent() before replacing the map and drop the input extent map on failure.
Which versions are affected by CVE-2026-89644?
How do I fix CVE-2026-89644?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-89644 being exploited?
There is no known exploitation of CVE-2026-89644 in the wild and no public exploit code.
Sources
Also known as AZL-100610, BELL-CVE-2026-89644, DEBIAN-CVE-2026-89644, GHSA-8844-3wf4-22v2, UBUNTU-CVE-2026-89644.