CVE-2026-64283: KVM: guest_memfd: Treat memslot binding offset+size as unsigned values

High 7.0 EPSS 0.1% Linux kernel

In the Linux kernel, the following vulnerability has been resolved: KVM: guest_memfd: Treat memslot binding offset+size as unsigned values When binding a memslot to a guest_memfd file, treat the offset and size as unsigned values to fix a bug where the sum of the two can result in a false negative when checking for overflow against the size of the file. Passing unsigned values also avoids relying on somewhat obscure checks in other flows for safety, and tracks the offset and size as they are intended to be tracked, as unsigned values. On 64-bit kernels, the number of pages a memslot contains and thus the size (and offset) of its guest_memfd binding are unsigned 64-bit values. Taking the offset+size as an loff_t instead of a uoff_t inadvertently converts the unsigned value to a signed value if the offset and/or size is massive. Locally storing the offset and size as signed values is benign in and of itself (though even that is *extremely* difficult to discern), but operating on their sum is not. For the offset, KVM explicitly checks against a negative value, which might seem like a bug as KVM could incorrectly reject a legitimate binding, but that's not actually the case as KVM_CREATE_GUEST_MEMFD takes a signed value for its size, i.e. a would-be-negative offset is also greater than the maximum possible size of any guest_memfd file. Regarding the size, while KVM lacks an explicit check for a negative value, i.e. seemingly has a flawed overflow check, KVM restricts the number of pages in a single memslot to the largest positive signed 32-bit value: if (id < KVM_USER_MEM_SLOTS && (mem->memory_size >> PAGE_SHIFT) > KVM_MEM_MAX_NR_PAGES) return -EINVAL; and so that maximum "size" will ever be is 0x7fffffff000. The sum of the two is, however, problematic. While the size is restricted by KVM's memslot logic, the offset is not, i.e. the offset is completely unchecked until the "offset + size > i_size_read(inode)" check. If the offset is the (nearly) largest possible _positive_ value, then adding size to the offset can result in a signed, negative 64-bit value. When compared against the size of the file (guaranteed to be positive), the negative sum is always smaller, and KVM incorrectly allows the absurd offset. Opportunistically add missing includes in kvm_mm.h (instead of relying on its parents).

• CVE-2026-64283CVE identifier
• 7.0CVSS 3.1 base score (high)
• 0.1%EPSS: chance of exploitation in the next 30 days (higher than 4% of CVEs)
• 2026-07-25published

What do these terms mean? CVE · CVSS score · exploited (KEV) · EPSS · backported fix · all terms

Affected and fixed versions

Affected:

• Linux Linux a7800aa80ea4d5356b8474c2302812e9d4926fa6 to before e4683654881f3303ab286e45df6f91c0675d867c
• Linux Linux a7800aa80ea4d5356b8474c2302812e9d4926fa6 to before 3f9c0fdefa0431ad7a5528d76b9cdad912500bdf
• Linux Linux a7800aa80ea4d5356b8474c2302812e9d4926fa6 to before f3a98d5881b9bd4807f49156143565f6aabcef1e
• Linux Linux a7800aa80ea4d5356b8474c2302812e9d4926fa6 to before eba85fee7fc6cf28fec38a5bf3c378bef9a79ca6
• Linux Linux 6.8

Patch it

Use the commands for your system. Distribution packages often keep an older version number with the fix backported, so compare with the fixed package versions in the table below, not only with the upstream version.

sudo apt update
sudo apt install --only-upgrade linux-image-amd64

sudo apt update
sudo apt install --only-upgrade linux-image-generic (or the installed flavour: linux-image-aws, -azure, -gcp, -virtual)

sudo dnf upgrade --refresh kernel

sudo dnf upgrade --refresh kernel

sudo zypper refresh
sudo zypper update kernel-default

sudo dnf upgrade --releasever=latest kernel kernel6.12

sudo pacman -Syu

apk update && apk upgrade linux-lts linux-virt

not Linux

General update steps for every system are on the Linux and Unix & BSD pages; after updating, see which services to restart.

Fix status in Linux distributions

From the Debian security tracker, Ubuntu CVE tracker and Red Hat Security Data API, refreshed every few hours.

Sources

• https://git.kernel.org/stable/c/e4683654881f3303ab286e45df6f91c0675d867c
• https://git.kernel.org/stable/c/3f9c0fdefa0431ad7a5528d76b9cdad912500bdf
• https://git.kernel.org/stable/c/f3a98d5881b9bd4807f49156143565f6aabcef1e
• https://git.kernel.org/stable/c/eba85fee7fc6cf28fec38a5bf3c378bef9a79ca6
• CVE-2026-64283 on CVE.org
• CVE-2026-64283 on NVD

Page generated automatically from official sources on 2026-11-03 18:05 UTC. Always confirm with your vendor's advisory.