VulnerabilityPublished 25 Jul 2026Updated 21 Oct 2026

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

Affects Linux kernelSource CVE Database V5

Not known to be exploited · fixed in f3a98d5881b9bd4807f49156143565f6aabcef1e : update Linux kernel when convenient.

Data as of 26 Oct 2026, 14:05 UTC

Severity

Unrated

Rated by Threat Radar · No CVSS score from NVD or the CNA

EPSS: 0.1% chance of exploitation in 30 days – higher than 4% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in f3a98d5881b9bd4807f49156143565f6aabcef1e, eba85fee7fc6cf28fec38a5bf3c378bef9a79ca6, e4683654881f3303ab286e45df6f91c0675d867c +1

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade Linux kernel to f3a98d5881b9bd4807f49156143565f6aabcef1e, eba85fee7fc6cf28fec38a5bf3c378bef9a79ca6, e4683654881f3303ab286e45df6f91c0675d867c or 3f9c0fdefa0431ad7a5528d76b9cdad912500bdf.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ a7800aa80ea4d5356b8474c2302812e9d4926fa6, < f3a98d5881b9bd4807f49156143565f6aabcef1e	Fixed in f3a98d5881b9bd4807f49156143565f6aabcef1e
LinuxLinux	Affected ≥ a7800aa80ea4d5356b8474c2302812e9d4926fa6, < eba85fee7fc6cf28fec38a5bf3c378bef9a79ca6	Fixed in eba85fee7fc6cf28fec38a5bf3c378bef9a79ca6
LinuxLinux	Affected ≥ a7800aa80ea4d5356b8474c2302812e9d4926fa6, < e4683654881f3303ab286e45df6f91c0675d867c	Fixed in e4683654881f3303ab286e45df6f91c0675d867c
LinuxLinux	Affected ≥ a7800aa80ea4d5356b8474c2302812e9d4926fa6, < 3f9c0fdefa0431ad7a5528d76b9cdad912500bdf	Fixed in 3f9c0fdefa0431ad7a5528d76b9cdad912500bdf
LinuxLinux	Affected =6.8	Fixed in–

Description

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).

References

Community reviews

Loading reviews…