CVE-2026-63941

Guest isolation bypass via uncapped ZCR_EL2 restore

Published Jul 19, 2026 · Updated Jul 19, 2026

Privilege boundary violation in Linux Kernel 6.11 allows guest OS users to access unauthorized SVE vector lengths through nested KVM. The arm64 KVM restore path writes a guest hypervisor's raw ZCR_EL2.LEN value to hardware when that value was changed through the nontrapping ZCR_EL1 accessor. Exploitation requires code execution in a VHE guest hypervisor with nested virtualization and SVE enabled, allowing an L2 guest to exceed its configured vector-length limit.

CVSS severity8.8
High
EPSS probability0.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Privilege boundary violation in Linux Kernel 6.11 allows guest OS users to access unauthorized SVE vector lengths through nested KVM. The arm64 KVM restore path writes a guest hypervisor's raw ZCR_EL2.LEN value to hardware when that value was changed through the nontrapping ZCR_EL1 accessor. Exploitation requires code execution in a VHE guest hypervisor with nested virtualization and SVE enabled, allowing an L2 guest to exceed its configured vector-length limit.

The record

CVE
CVE-2026-63941
Published
Jul 19, 2026
Updated
Jul 19, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 19, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=6.11
  2. Affected versionversion=b3d29a8230998b36afecf494b199211d26052785 <742a9b5ccd8c46caf983ca90c94f855466968e34
  3. Affected versionversion=b3d29a8230998b36afecf494b199211d26052785 <83726330748981372bde86ed5411d7b306612991

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=6.11; version=b3d29a8230998b36afecf494b199211d26052785 <742a9b5ccd8c46caf983ca90c94f855466968e34; version=b3d29a8230998b36afecf494b199211d26052785 <83726330748981372bde86ed5411d7b306612991

Published CVSS scores

8.8kernel.orgCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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