CVE-2021-4023

What it actually does

The flaw permits a local user to trigger a kernel panic by submitting new io-uring operations during an io-workqueue cancellation when free space is exhausted.

Why it matters to the business

Local users can crash affected systems on demand, causing unplanned downtime, service interruption, and potential loss of in-memory data or unsaved work.

How an attack unfolds

An attacker with local access and io-uring permissions issues a crafted sequence of io-uring requests that forces an improper cancellation path, exhausting free space and submitting new operations, which panics the kernel.

How to fix it

Upgrade the Linux kernel to version 5.15-rc1 or later on all affected distributions; apply vendor backports where available and reboot systems after installation.

How to confirm the fix worked

Confirm the running kernel is at least 5.15-rc1, then exercise io-uring workloads under cancellation scenarios in a test environment to verify absence of panic.

Typical attack path

1. Gain local shell or process execution on the target
2. Obtain permissions to issue io-uring syscalls
3. Prepare a request pattern that triggers cancellation under space pressure
4. Execute the pattern to induce immediate kernel panic

How to detect it

Review kernel crash dumps and dmesg output for io-workqueue or io_uring panic signatures; correlate with processes that use io_uring syscalls around the time of the crash.

• io_uring.*workqueue.*panic
• io_cancel.*submission.*shortage
• kernel BUG at io_uring/

What your security team should do

• Prioritize kernel upgrades on internet-facing or multi-tenant systems
• Disable io_uring via kernel command-line or seccomp where the feature is unnecessary
• Monitor kernel logs for io-workqueue related panics until patches are deployed