CVE-2025-40233 ocfs2: clear extent cache after moving/defragmenting extents
A stale extent cache in the Linux kernel OCFS2 filesystem can trigger a BUG_ON crash during specific file operations, causing a 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-2025-40233?
CVE-2025-40233 is a high-severity denial of service vulnerability in Linux, published on 4 Dec 2025. 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:
ocfs2: clear extent cache after moving/defragmenting extents
The extent map cache can become stale when extents are moved or defragmented, causing subsequent operations to see outdated extent flags. This triggers a BUG_ON in ocfs2_refcount_cal_cow_clusters().
The problem occurs when: 1. copy_file_range() creates a reflinked extent with OCFS2_EXT_REFCOUNTED 2. ioctl(FITRIM) triggers ocfs2_move_extents() 3. __ocfs2_move_extents_range() reads and caches the extent (flags=0x2) 4. ocfs2_move_extent()/ocfs2_defrag_extent() calls __ocfs2_move_extent() which clears OCFS2_EXT_REFCOUNTED flag on disk (flags=0x0) 5. The extent map cache is not invalidated after the move 6. Later write() operations read stale cached flags (0x2) but disk has updated flags (0x0), causing a mismatch 7. BUG_ON(!(rec->e_flags & OCFS2_EXT_REFCOUNTED)) triggers
Fix by clearing the extent map cache after each extent move/defrag operation in __ocfs2_move_extents_range(). This ensures subsequent operations read fresh extent data from disk.
Which versions are affected by CVE-2025-40233?
How do I fix CVE-2025-40233?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-40233 being exploited?
There is no known exploitation of CVE-2025-40233 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40233, DEBIAN-CVE-2025-40233, GHSA-pmpf-32ww-gfmp, ROOT-OS-DEBIAN-11-CVE-2025-40233, ROOT-OS-UBUNTU-2404-CVE-2025-40233, UBUNTU-CVE-2025-40233.