CVE-2026-74356 vhost: fix vhost_get_avail_idx for a non empty ring
A logic error in the Linux kernel vhost driver causes a host livelock when mergeable buffers are enabled and the guest stalls, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-74356?
CVE-2026-74356 is a high-severity denial of service vulnerability in Linux, published on 15 Aug 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:
vhost: fix vhost_get_avail_idx for a non empty ring
vhost_get_avail_idx is supposed to report whether it has updated vq->avail_idx. Instead, it returns whether all entries have been consumed, which is usually the same. But not always - in drivers/vhost/net.c and when mergeable buffers have been enabled, the driver checks whether the combined entries are big enough to store an incoming packet. If not, the driver re-enables notifications with available entries still in the ring. The incorrect return value from vhost_get_avail_idx propagates through vhost_enable_notify and causes the host to livelock if the guest is not making progress, as vhost will immediately disable notifications and retry using the available entries.
This goes back to commit d3bb267bbdcb ("vhost: cache avail index in vhost_enable_notify()") which changed vhost_enable_notify() to compare the freshly read avail index against vq->last_avail_idx instead of the previously cached vq->avail_idx. Commit 7ad472397667 ("vhost: move smp_rmb() into vhost_get_avail_idx()") then carried over the same comparison when refactoring vhost_enable_notify() to call the unified vhost_get_avail_idx().
The obvious fix is to make vhost_get_avail_idx do what the comment says it does and report whether new entries have been added.
Which versions are affected by CVE-2026-74356?
How do I fix CVE-2026-74356?
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-2026-74356 being exploited?
There is no known exploitation of CVE-2026-74356 in the wild and no public exploit code.
Sources
Also known as AZL-96390, BELL-CVE-2026-74356, DEBIAN-CVE-2026-74356, GHSA-pp6m-qvmq-968c, UBUNTU-CVE-2026-74356.