VulnerabilityPublished 19 Jul 2026Updated 20 Jul 2026

CVE-2026-63807: Linux kernel · KVM: x86/mmu: Ensure hugepage is in by slot before checking max mapping level

Source GCVE Database

Authoritative record:CVE-2026-63807· High 8.8

Not known to be exploited · CVSS 8.8 High · fixed in ef057cbf825e03b63f6edf5980f96abf3c53089d : patch Linux kernel soon.

Data as of 26 Oct 2026, 15:59 UTC

CVSS 3.1 base score

8.8High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.1% chance of exploitation in 30 days – higher than 6% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in ef057cbf825e03b63f6edf5980f96abf3c53089d, c5c29b3c268332afe67d598a034c58344540ed92, b2ae3245ea44dccaa9af676b6747476951883318 +4

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Attack Vector: Local
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Changed
Confidentiality: High
Integrity: High
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 19 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.

ghsa-xxf6-pvjr-qhj4

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 9eba50f8d7fcb61774f160890f98239fa3ab68a6, < ef057cbf825e03b63f6edf5980f96abf3c53089d	Fixed in ef057cbf825e03b63f6edf5980f96abf3c53089d
LinuxLinux	Affected ≥ 9eba50f8d7fcb61774f160890f98239fa3ab68a6, < c5c29b3c268332afe67d598a034c58344540ed92	Fixed in c5c29b3c268332afe67d598a034c58344540ed92
LinuxLinux	Affected ≥ 9eba50f8d7fcb61774f160890f98239fa3ab68a6, < b2ae3245ea44dccaa9af676b6747476951883318	Fixed in b2ae3245ea44dccaa9af676b6747476951883318
LinuxLinux	Affected ≥ 9eba50f8d7fcb61774f160890f98239fa3ab68a6, < 18587f9831612e24cd8f24be1ec15478feff7abc	Fixed in 18587f9831612e24cd8f24be1ec15478feff7abc
LinuxLinux	Affected ≥ 9eba50f8d7fcb61774f160890f98239fa3ab68a6, < 48b91ed7e22bb82571c34f8b80b6ecdc90a6fab8	Fixed in 48b91ed7e22bb82571c34f8b80b6ecdc90a6fab8
LinuxLinux	Affected ≥ 9eba50f8d7fcb61774f160890f98239fa3ab68a6, < 7b52008023b7facf40fba3ebe92449bda8ea53b9	Fixed in 7b52008023b7facf40fba3ebe92449bda8ea53b9

AI-suggested

A fix for this vulnerability has been implemented in the Linux kernel. Users should update to a kernel version that includes this patch. Since this is a kernel-level issue, remediation involves applying the official kernel update containing the fix. No additional mitigations are indicated or required beyond applying the patch.

Description

In the Linux kernel, the following vulnerability has been resolved: KVM: x86/mmu: Ensure hugepage is in by slot before checking max mapping level When recovering hugepages in the shadow MMU, verify that the base gfn of the shadow page is actually contained within the target memslot, *before* querying the max mapping level given the shadow page's gfn. Failure to pre-check the validity of the gfn can lead to an out-of-bounds access to the slot's lpage_info (which typically manifests as a host #PF because the lpage_info is vmalloc'd) if the guest creates a hugepage mapping (in its PTEs) that extends "below" the bounds of a memslot. When faulting in memory for a guest, and the size of the guest mapping is greater than KVM's (current) max mapping, then KVM will create a "direct" shadow page (direct in that there are no gPTEs to shadow, and so the target gfn is a direct calculation given the base gfn of the shadow page). The hugepage recovery flow looks for such direct shadow pages, as forcing 4KiB mappings when dirty logging generates the guest > host mapping size case. When the 4KiB restriction is lifted, then KVM can replace the shadow page with a hugepage. But if KVM originally used a smaller mapping than the guest because the range of memory covered by the guest hugepage exceeds the bounds of a memslot, then KVM will link a direct shadow page with a gfn that is outside the bounds of the memslot being used to fault in memory. The rmap entry added for the leaf mapping is correct and within bounds, but the gfn of the leaf SPTE's parent shadow page will be out of bounds. BUG: unable to handle page fault for address: ffffc90000806ffc #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 100000067 P4D 100000067 PUD 1002a7067 PMD 10612f067 PTE 0 Oops: Oops: 0000 [#1] SMP CPU: 13 UID: 1000 PID: 757 Comm: mmu_stress_test Not tainted 7.1.0-rc1-48ce1e26eace-x86_pir_to_irr_comments-vm #341 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:kvm_mmu_max_mapping_level+0x79/0x2b0 [kvm] Call Trace: <TASK> kvm_mmu_recover_huge_pages+0x21b/0x320 [kvm] kvm_set_memslot+0x1ee/0x590 [kvm] kvm_set_memory_region.part.0+0x3a1/0x4d0 [kvm] kvm_vm_ioctl+0x9bf/0x15d0 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0xb7/0xbb0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7f21c0f1a9bf </TASK> Don't bother pre-checking the bounds of the potential hugepage, i.e. don't check that e.g. sp->gfn + KVM_PAGES_PER_HPAGE(sp->role.level + 1) is also within the memslot, as the checks performed by kvm_mmu_max_mapping_level() are a superset of the basic bounds checks. I.e. pre-checking the full range would be a dubious micro-optimization.

Impact

If exploited, this vulnerability can cause a host kernel page fault due to out-of-bounds memory access in the KVM shadow MMU code. This could lead to host instability or crashes when handling guest memory mappings involving hugepages that extend beyond memslot boundaries. There is no indication of code execution or privilege escalation from the provided data. No known exploits in the wild have been reported.

Summary

The vulnerability in the Linux kernel's KVM x86 MMU component involves improper validation when recovering hugepages in the shadow MMU. Specifically, the base gfn of a shadow page was not checked to confirm it lies within the target memory slot before determining the maximum mapping level. This flaw could lead to an out-of-bounds access of the memslot's lpage_info structure, typically causing a host page fault (#PF). The issue manifests when a guest creates a hugepage mapping that extends below the memslot bounds, causing KVM to link a direct shadow page with an out-of-bounds gfn. The patch corrects this by verifying the gfn is contained within the memslot prior to further processing, preventing invalid memory accesses in the host kernel.

References

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