CVE-2026-98719 KVM: SEV: Nullify "have run CPUs" mask pointer when freeing it
A double-free vulnerability in Linux KVM SEV initialization allows local attackers to potentially execute code or escalate privileges.
- 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-2026-98719?
CVE-2026-98719 is an use after free vulnerability in Linux, published on 18 Oct 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: SEV: Nullify "have run CPUs" mask pointer when freeing it
Nullify have_run_cpus when freeing the mask, particularly in the error path of __sev_guest_init(), so that KVM doesn't have to subtly use sev->active to track whether or not the mask has been freed. As pointed out by Sashiko, blindly freeing the mask in sev_vm_destroy() results in a double-free if the mask is freed if __sev_guest_init() fails.
Throw the logic in a helper as nullifying the pointer is frustratingly difficult and weird due to have_run_cpus being a single-entry array when CPUMASK_OFFSTACK=n. Deliberately don't use CPUMASK_VAR_NULL, as it's not directly assignable when the cpumask is on-stack, e.g. requires using a local variable and a memcpy(), which is beyond ridiculous. Furthermore, while clearing the on-stack bitmask is an unnecessary and arguably unwanted side effect, KVM absolutely relies on '0' being the "null" value given that the struct is zero-allocated.
Opportunistically add an alloc() helper to pair with free(); there are just enough call sites to make doing so worthwhile.
Which versions are affected by CVE-2026-98719?
How do I fix CVE-2026-98719?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-98719 being exploited?
There is no known exploitation of CVE-2026-98719 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-98719, DEBIAN-CVE-2026-98719, GHSA-j294-cf74-gq7q, UBUNTU-CVE-2026-98719.