CVE-2026-98639 KVM: riscv: Fix NACL hfence entry update order
A race condition in Linux KVM RISC-V allows incorrect TLB flush ranges, potentially leading to data exposure or modification by a local attacker.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-98639?
CVE-2026-98639 is a 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: riscv: Fix NACL hfence entry update order
The SBI v3.0 specification (section 15.1.2) requires a nested HFENCE entry to be populated as follows: 1) find an unused entry with Config.Pending == 0 2) update the Page_Number and Page_Count words 3) update the Config word with Config.Pending set
__kvm_riscv_nacl_hfence() writes the Config word first, so the SBI implementation (or NACL hardware) can observe a pending entry with pnum/pcount values left over from the previous use of that entry, resulting in incorrect TLB flush ranges.
Write pnum and pcount first and the Config word last. Since the consumer is an external agent on coherent shared memory, use WRITE_ONCE() to stop the compiler from reordering the stores and smp_wmb() to make the parameter words globally visible before the Pending bit is set.
Which versions are affected by CVE-2026-98639?
How do I fix CVE-2026-98639?
Apply the vendor's patch.
Is CVE-2026-98639 being exploited?
There is no known exploitation of CVE-2026-98639 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-98639, DEBIAN-CVE-2026-98639, GHSA-2qhr-3xrg-mw89, UBUNTU-CVE-2026-98639.