CVE-2021-4147

What it actually does

A malicious guest can trigger continuous reboots that deadlock or crash the libvirtd process on the host, resulting in denial of service.

Why it matters to the business

Virtualization hosts become unavailable, disrupting operations for all hosted workloads until the service is restarted.

How an attack unfolds

An attacker with control of a guest VM repeatedly initiates reboots, causing the host management daemon to enter a deadlock or crash state.

How to fix it

Upgrade to a fixed version of the affected software as listed in the provided per-package fixes.

How to confirm the fix worked

Confirm the installed version matches one of the listed fixed versions and verify that continuous guest reboots no longer cause host daemon failure.

Typical attack path

1. Gain control of a guest virtual machine
2. Trigger repeated reboot cycles from within the guest
3. Observe or confirm host daemon deadlock or crash

How to detect it

Review virtualization host logs for repeated guest reboot patterns followed by libvirtd crashes or deadlocks.

What your security team should do

• Apply the listed fixed versions immediately
• Monitor for repeated guest reboot events
• Limit guest privileges where possible to reduce reboot abuse