CVE-2026-90095 fuse: Fix the condition to enable over-io-uring
A race condition in the Linux kernel FUSE io-uring implementation can cause deadlocks, leading to denial of service for local users.
- 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-2026-90095?
CVE-2026-90095 is a vulnerability in Linux, published on 17 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:
fuse: Fix the condition to enable over-io-uring
The existing condition in fuse_uring_cmd() is there only to avoid disabling io-uring for connections that already run with it, missing was a condition to refuse any IORING_OP_URING_CMD if the connection/channel didn't get enabled because of missing FUSE_INIT reply flag FUSE_OVER_IO_URING. Without the reply flag the barrier in fuse_uring_ready() doesn't work and IO could already be going on and cause deadlock states (at a minimum one between fch->bg_lock and queue->lock).
The change itself is trivial, but brings behavior change, FUSE_OVER_IO_URING has to be set in the FUSE_INIT_REPLY by fuse servers to accept any IORING_OP_URING_CMD. Libfuse does that and the only non-libfuse implementation I found (fractal-fuse) also does it. Qemu patches for fuse-io-uring are not merged yet, as far as I know.
Moved up is the smp_load_acquire(&fch->initialized) check, as a fuse-server implementation might try to setup io-uring before FUSE_INIT is processed and might have gotten -EOPNOTSUPP instead of -EAGAIN.
Also fixed is a stale comment that explains the handling of the FUSE_OVER_IO_URING flag in early RFC versions.
If there should be a report from any library or application we probably need to revert this commit.
Which versions are affected by CVE-2026-90095?
How do I fix CVE-2026-90095?
Apply the vendor's patch.
Is CVE-2026-90095 being exploited?
There is no known exploitation of CVE-2026-90095 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-90095, DEBIAN-CVE-2026-90095, GHSA-f6c3-623p-967p, UBUNTU-CVE-2026-90095.