CVE-2026-64326 block: skip sync_blockdev() on surprise removal in bdev_mark_dead()
A missing check in the Linux kernel block layer causes a hang during surprise device removal, leading to 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-2026-64326?
CVE-2026-64326 is a medium-severity denial of service vulnerability in Linux kernel, published on 25 Jul 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:
block: skip sync_blockdev() on surprise removal in bdev_mark_dead()
bdev_mark_dead()'s @surprise == true means the device is already gone. The filesystem callback fs_bdev_mark_dead() honours this and skips sync_filesystem(), but the bare block device path (no ->mark_dead op) lost its !surprise guard when the holder ->mark_dead callback was wired up (see Fixes), and now calls sync_blockdev() unconditionally, which can hang forever waiting on writeback that can no longer complete.
syzkaller hit this via nvme_reset_work()'s "I/O queues lost" path: nvme_mark_namespaces_dead() -> blk_mark_disk_dead() -> bdev_mark_dead(bdev, true) -> sync_blockdev() blocks in folio_wait_writeback(), wedging the reset worker and every task waiting on it.
Skip the sync on surprise removal, matching fs_bdev_mark_dead(); invalidate_bdev() still runs. Orderly removal (surprise == false) is unchanged.
Found by FuzzNvme(Syzkaller with FEMU fuzzing framework).
Which versions are affected by CVE-2026-64326?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-64326?
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-2026-64326 being exploited?
There is no known exploitation of CVE-2026-64326 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-93458, BELL-CVE-2026-64326, DEBIAN-CVE-2026-64326, GHSA-h8v6-c5rc-5j48, ROOT-OS-UBUNTU-2204-CVE-2026-64326, UBUNTU-CVE-2026-64326.