CVE-2021-28710

Guest-to-host privilege escalation via unstripped page-table root

Published Nov 21, 2021 · Updated Aug 3, 2024

Privilege escalation in Xen Hypervisor 4.15 allows guest OS users to gain host privileges through shared IOMMU and EPT page tables. In the shared-page-table setup path, Xen leaves a four-level EPT root intact when programming an IOMMU that requires three levels, exposing leaf entries to guest writes. Exploitation requires an Intel x86 host with an affected IOMMU, an HVM guest with PCI passthrough, and shared IOMMU/EPT page tables.

CVSS severity8.8
High
EPSS probability0.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Privilege escalation in Xen Hypervisor 4.15 allows guest OS users to gain host privileges through shared IOMMU and EPT page tables. In the shared-page-table setup path, Xen leaves a four-level EPT root intact when programming an IOMMU that requires three levels, exposing leaf entries to guest writes. Exploitation requires an Intel x86 host with an affected IOMMU, an HVM guest with PCI passthrough, and shared IOMMU/EPT page tables.

The record

CVE
CVE-2021-28710
Published
Nov 21, 2021
Updated
Aug 3, 2024
Vendor
Xen Project
Product
Xen Hypervisor
Classifications
CWE-269, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Nov 21, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record 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=4.15.x <unspecified

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Xen Project · Xen Hypervisorversion=4.15.x <unspecified

Published CVSS scores

6.9NIST NVDAV:L/AC:M/Au:N/C:C/I:C/A:C
8.8NIST NVDCVSS: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

CWE-269Improper Privilege Management
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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