CVE-2026-89915 KVM: arm64: Remove VM-wide VNCR mapping counter
A race condition in KVM arm64 TLB invalidation logic can cause missed invalidations, potentially 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-2026-89915?
CVE-2026-89915 is a critical vulnerability in Linux, published on 16 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:
KVM: arm64: Remove VM-wide VNCR mapping counter
The global VNCR mapping counter is used to decide whether an L1 provided VNCR page is mapped in L0 on any CPU at the point of dealing with a TLB invalidation. It is incremented when a mapping is made in the fixmap, and decremented when unmapped.
As it turns out, this tracking has several flaws:
- we are trying to invalidate TLBs, and the mapping is only an opportunistic consequence of the TLB. Checking this counter to decide whether a TLB needs to be invalidated may result in missed invalidations.
- an L1 vcpu invalidating its own TLB (a very likely case) will not succeed in invalidating the VNCR pseudo TLB because that page is not mapped in L0 at this stage.
Given that this tracking fails at delivering the minimum guarantees that are required and is only a performance optimisation, remove it completely.
Which versions are affected by CVE-2026-89915?
How do I fix CVE-2026-89915?
Apply the vendor's patch.
Is CVE-2026-89915 being exploited?
There is no known exploitation of CVE-2026-89915 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-89915, DEBIAN-CVE-2026-89915, GHSA-crqv-c33h-f779, UBUNTU-CVE-2026-89915.