This CVE exposes a race condition in the fuse-uring subsystem where a fuse request becomes visible to userspace before the kernel has finished initializing it. The vulnerability is a classic TOCTOU (time-of-check-to-time-of-use) issue: the kernel copies request data into userspace-accessible buffers, then exposes that request through the io_uring submission queue — but the initialization work isn't complete when the request becomes discoverable. A malicious userspace process can race to access the partially-initialized request, reading uninitialized kernel memory or corrupting internal state before the kernel finishes setting it up.
If you're running a kernel with fuse-uring support enabled, check whether any userspace applications are submitting io_uring SQE operations targeting the fuse character device (/dev/fuse). The attack surface requires the attacker to have the ability to issue io_uring submission queue entries — typically meaning either local code execution or a compromised container/process with uring syscall access. The vulnerable window exists between when the kernel copies request data via memcpy and when it calls fuse_uring_add_to_pq() to enqueue the prepared request; the fix reorders this so the enqueue happens after memcpy completes.
What makes this worth more than a one-off patch: the pattern of async ring buffer state becoming visible before preparation completes has now appeared across multiple io_uring wrappers around existing kernel subsystems. This isn't coincidence — io_uring's async completion model was grafted onto synchronous request-tracking code without a defined protocol for when requests become externally visible. The fix here closes this specific instance, but the interaction surface between uring and legacy subsystems warrants scrutiny in any code review involving io_uring operations against kernel objects that predated uring support. Watch for any code path where userspace can poll or read state from an io_uring ring while a kernel operation is still in flight — that's the fingerprint of this vulnerability class.