CVE-2026-52969 KVM: Reject wrapped offset in kvm_reset_dirty_gfn()
A local attacker with access to /dev/kvm can exploit an integer overflow in KVM dirty ring handling to achieve out-of-bounds memory access and potential privilege escalation.
- 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-2026-52969?
CVE-2026-52969 is a high-severity vulnerability in Linux kernel, published on 24 Jun 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: Reject wrapped offset in kvm_reset_dirty_gfn()
kvm_reset_dirty_gfn() guards the gfn range with
if (!memslot || (offset + __fls(mask)) >= memslot->npages) return;
but offset is u64 and the addition is unchecked. The check can be silently bypassed by a u64 wrap.
The dirty ring backing those entries is MAP_SHARED at KVM_DIRTY_LOG_PAGE_OFFSET of the vcpu fd, so the VMM can rewrite the slot and offset fields of any entry between when the kernel pushes them and when KVM_RESET_DIRTY_RINGS consumes them. On reset, kvm_dirty_ring_reset() re-reads the values via READ_ONCE() and feeds them straight back into this check; only the flags handshake is treated as the handover, the slot/offset payload is taken on trust.
Crafting two entries
entry[i].offset = 0xffffffffffffffc1 entry[i+1].offset = 0
makes the coalescing loop in kvm_dirty_ring_reset() compute
delta = (s64)(0 - 0xffffffffffffffc1) = 63
which falls in [0, BITS_PER_LONG), so it folds entry[i+1] into the existing mask by setting bit 63. The trailing kvm_reset_dirty_gfn() call then sees offset = 0xffffffffffffffc1 and __fls(mask) = 63; the sum is 0 in u64 and the bounds check passes.
That offset propagates into kvm_arch_mmu_enable_log_dirty_pt_masked() unchanged. On the legacy MMU path -- kvm_memslots_have_rmaps() == true, i.e. shadow paging, any VM that has allocated shadow roots, or a write-tracked slot -- it reaches gfn_to_rmap(), which indexes slot->arch.rmap[0][] with a near-U64_MAX gfn. That is an out-of-bounds load of a kvm_rmap_head, followed by a conditional clear of PT_WRITABLE_MASK in whatever the loaded pointer points at. The path is reachable from any process holding /dev/kvm.
Range-check offset on its own first, so the addition cannot wrap. memslot->npages is bounded well below U64_MAX, so once offset < npages holds, offset + __fls(mask) (with __fls(mask) < BITS_PER_LONG) stays in range.
Which versions are affected by CVE-2026-52969?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-52969?
Apply the vendor's patch.
Is CVE-2026-52969 being exploited?
There is no known exploitation of CVE-2026-52969 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-52969, DEBIAN-CVE-2026-52969, GHSA-gpq6-rrxf-v33x, ROOT-OS-DEBIAN-12-CVE-2026-52969, ROOT-OS-UBUNTU-2204-CVE-2026-52969, ROOT-OS-UBUNTU-2404-CVE-2026-52969 and 1 more.