x86/AMD: ineffectual Zenbleed workaround

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-79608
StatePUBLISHED
AssignerXEN
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-13 16:17:23 UTC
Updated2026-10-20 18:17:21 UTC
DescriptionThe workaround for XSA-433 (Zenbleed, CVE-2023-20593) was later re-worked to better integrate with other manipulations of the same MSR. In this rework an inverted conditional was introduced, resulting in the workaround to not be applied when needed and vice versa. For more details, see: http://xenbits.xen.org/xsa/advisory-433.html

Risk And Classification

Primary CVSS: v3.1 9.8 CRITICAL from ADP

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

EPSS: 0.001590000 probability, percentile 0.046080000 (date 2026-10-20)

Problem Types: CWE-670 | CWE-670 CWE-670 Always-Incorrect Control Flow Implementation

VersionSourceTypeScoreSeverityVector
3.1ADPDECLARED9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
3.1134c704f-9b21-4f2e-91b3-4a467353bcc0Secondary9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Xen Xen unknown consult Xen advisory XSA-515 Not specified

References

ReferenceSourceLinkTags
xenbits.xenproject.org/xsa/advisory-515.html [email protected] xenbits.xenproject.org
xenbits.xen.org/xsa/advisory-515.html af854a3a-2127-422b-91ae-364da2661108 xenbits.xen.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: This issue was discovered by Sashiko + Opus 5.0 and diagnosed as a security issue by George Dunlap. (en)

Additional Advisory Data

Workarounds

CNA: This issue can be mitigated by disabling AVX, either by booting Xen with `cpuid=no-avx` on the command line, or by specifying `cpuid="host:avx=0"` in the vm.cfg file of all untrusted VMs. However, this will come with a significant impact on the system and is not recommended for anyone able to deploy the microcode or patch described below.

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