CVE-2026-63938

Guest-to-host escape via unchecked PSC buffer indices

Published Jul 19, 2026 · Updated Jul 19, 2026

Out-of-bounds access in Linux Kernel KVM SEV allows guest OS users to escape a VM through a crafted Page State Change request. The snp_begin_psc function compares guest-controlled entry indices with a fixed protocol maximum instead of the effective GHCB scratch-buffer capacity, allowing reads and writes beyond that buffer. Code execution inside an SEV-SNP guest is required; successful exploitation crosses the guest-host boundary and exposes or corrupts host kernel memory.

CVSS severity9.3
Critical
EPSS probability0.18%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds access in Linux Kernel KVM SEV allows guest OS users to escape a VM through a crafted Page State Change request. The snp_begin_psc function compares guest-controlled entry indices with a fixed protocol maximum instead of the effective GHCB scratch-buffer capacity, allowing reads and writes beyond that buffer. Code execution inside an SEV-SNP guest is required; successful exploitation crosses the guest-host boundary and exposes or corrupts host kernel memory.

The record

CVE
CVE-2026-63938
Published
Jul 19, 2026
Updated
Jul 19, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-1285, T1068
Attack vector
local
Privileges
unauthenticated

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=9b54e248d2644be71cb394eb85f31ad99e023a05 <121d88de56bc5c0ba0ce2f6381af67f948a7e7c1
  3. Affected versionversion=9b54e248d2644be71cb394eb85f31ad99e023a05 <505a3b94535583e4265360e2621734e355ef263d
  4. Affected versionversion=9b54e248d2644be71cb394eb85f31ad99e023a05 <5198f70c09a5f6e9e5f5a0a2c6b388f24294b176
  5. Affected versionversion=9b54e248d2644be71cb394eb85f31ad99e023a05 <75c8d1d7291268b479794fba5808971dc2f5eaf3

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=6.11; version=9b54e248d2644be71cb394eb85f31ad99e023a05 <121d88de56bc5c0ba0ce2f6381af67f948a7e7c1; version=9b54e248d2644be71cb394eb85f31ad99e023a05 <505a3b94535583e4265360e2621734e355ef263d; version=9b54e248d2644be71cb394eb85f31ad99e023a05 <5198f70c09a5f6e9e5f5a0a2c6b388f24294b176; version=9b54e248d2644be71cb394eb85f31ad99e023a05 <75c8d1d7291268b479794fba5808971dc2f5eaf3

Published CVSS scores

9.3Linux CNACVSS:3.1/AV:L/AC:L/PR:N/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 11, 2026Sep 17, 2026
Latest reporting daySep 17, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1285Improper Validation of Specified Index, Position, or Offset in Input
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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